All About Hypertension (High Blood Pressure)	All About Urinalysis (Urine Tests): USG, Proteinuria Infections Etc.
When Kidneys are Enlarged (Renomegaly)	Other Diagnostic Tests (Ultrasound, X-Rays, Biopsies Etc.)

Introduction

Many of the symptoms of CRF, such as increased thirst and weight-loss, can also be symptoms of other diseases, so you need a diagnosis by your vet to be certain that you are dealing with CRF. The various test results will also tell you and your vet where any imbalances exist, which will help you to decide on the best treatments. 

The Various Tests and What They Mean

Choosing a Vet

If you want to be able to give your cat the best possible treatment, you need a good vet with whom you can work in partnership. A good vet can make all the difference to your cat's quality of life and chances of survival. I do not wish to disparage vets, who work very hard to qualify, and most of whom genuinely love animals; but as in every other profession, some vets are good, others not so good, and a small percentage very poor, so it is essential that you can recognise a bad vet - your cat's life depends upon finding a good one.  But even the best vet may not have time to keep fully up to date on developments in the treatment of CRF, so it may be helpful for you to find recent reference articles for your vet to read, for example.  

I maintain a private list of British vets who permit sub-Qs. If you are in the UK and need such a vet, please read here about how to obtain details of any vets in your area, though unfortunately the list is very short, so the chances of such a vet being in your area are sadly rather low.

Special Needs Pets has useful information on choosing a vet, and on working together. 

Veterinary Partner also has helpful suggestions

Linda's Feline CRF Hints are also helpful.

Vet Recommendations is a list of vets recommended by people with CRF cats.

Feline Good gives details of the five British specialists in feline medicine (Sarah Caney is no longer in Hampshire).

The Feline Advisory Bureau gives details of feline residents which it sponsors at a number of British veterinary schools.

The American Veterinary Medical Association mentions that if you change vets, your previous vet is obliged to provide copies of your cat's medical records if requested (see Section VII D).

A Second Opinion

If you are concerned about your vet's approach, you may wish to seek a second opinion. This is not always easy, but there are a couple of options available:

Cornell University College of Veterinary Medicine Dr Louis J Camuti Memorial Feline Consultation Service offers advice on feline health-related issues. You need to provide as much information as possible (e.g. blood test results), then the consultant will contact you or your vet to discuss your cat's situation, usually on the same day that you contact them. The service costs US$55 and is available Mondays, Wednesdays, and Fridays, 9 a.m. - 12 p.m. and 2 p.m. - 4p.m. US Eastern standard time (not holidays). Cornell has an excellent reputation and I have heard from several people who have used this service, most of whom were very satisfied, though one person was concerned (as was I) when the vet suggested ACE inhibitors for her cat with high bloodwork values.

Dr Nik Weber, a specialist in feline medicine, will consult with you or your vet for US$150. He will not undermine your vet or his/her advice, but rather he aims to provide additional input for difficult cases, particularly where there are no specialists locally. Dr Weber will consult internationally. A lady I have "known" (online) for some years has used him as her primary vet in the past and speaks highly of him.

Blood Tests: Which to Have

Some vets only test blood urea nitrogen (BUN) or urea, or possibly both blood urea nitrogen (or urea) and creatinine to start with. If these are elevated, or if you get to choose which tests are run, I recommend that you ask for full tests to be done as follows:

1. a blood chemistry panel, which checks kidney function and looks for any other abnormalities caused by poorly functioning kidneys; and

2. a complete blood count (CBC), which looks at the cat’s blood cells. This enables the vet to check for anaemia and infections, both common problems in CRF cats.

3. a urinalysis, which examines the cat's urine. This enables the vet to see if your cat is concentrating urine (CRF cats struggle to do this) and to check for urinary tract infections and protein in the urine.

4. a blood pressure check. Many CRF cats have high blood pressure (hypertension) which can cause blindness among other problems, so it is very important to check for this.

5. a check for hyperthyroidism.

You may need to have the blood analysed at an external laboratory - the results can take between one and three days to come back. Some vets can run most of these tests in-house and have results within a couple of hours, which can be helpful if your cat is very sick.

I know tests can be stressful both for your cat and your wallet, but they are invaluable in deciding how to treat your cat most effectively. Not every problem is apparent from the cat's behaviour. Once you know what problems your cat is experiencing, you and your vet can tailor the treatments to meet his or her needs.

As a minimum, you should ask for the following tests (all of which are discussed below in more detail) to be run:

• Blood Urea Nitrogen (BUN) or urea

• Creatinine (Crea)

• Potassium (K+)

• Phosphorus (P or Pi)

• Calcium (Ca)

• Sodium (Na+)

• Packed Cell Volume (PCV) (your vet may test Haematocrit (HCT) instead)

• TCO2 (or CO2) if possible (not all laboratories can do this test)

• Blood Pressure

Keep your own records of your cat's symptoms and bloodwork results, so you can monitor trends and customise treatments with your vet's help.

Frequency of Testing

For early CRF, it is worth having tests run twice a year; if your cat has medium numbers (creatinine up to 300, USA 3.5), ask for tests more frequently, every 3-6 months. If the disease is more advanced, you should consider testing more frequently, every 1-3 months. Thomas was tested every 3-4 months, but as the disease progressed we switched to every 1-2 months. In all cases, check for high blood pressure regularly (see below). Naturally, if your cat seems to be deteriorating, you should seek your vet's advice regardless of whether a blood test is due.

If you are trying to control anaemia and/or phosphorus levels, it is reasonable to test these every couple of weeks until you have got things under control; and you should also monitor potassium, particularly when you begin supplementation. Try to balance the need to run tests in order to monitor and control disease progression with the need to not increase your cat's stress levels unnecessarily, and bear in mind that taking blood too frequently can worsen anaemia. 

If Your Cat Fights Blood Draws

Many cats find having blood taken very stressful. There are some ways to minimise this stress:

• Stay with your cat whilst the blood is drawn. Many vets like to take the cat "out the back" to draw blood but this can frighten the cat, whereas a familiar face (yours) can help keep the cat calm.

• For cats who fight blood draws like our Harpsie, it can be easier to take the blood from a hind leg rather than from the jugular vein in the neck. Our vet used to place a towel over Harpsie's head and draw blood from the leg. You would probably expect a towel over the head to make a cat freak out more but many cats find it calming. Taking blood this way takes longer than taking it from the jugular but overall it still worked better for Harpsie.

• For some cats, the "clothes peg" method may work well.

• Cats hate the smell of alcohol, so it is better not to dampen down their fur with alcohol before a blood draw because it increases their stress levels. It is unnecessary anyway unless your cat has a particularly weak immune system, e.g. s/he also has cancer. Washington State University College of Veterinary Medicine explains why this isn't necessary for sub-Qs (the same applies for blood draws).

Factors Which May Affect Test Results

Certain factors may affect test results, and in certain cases may make the results somewhat inaccurate. Stress, fasting before a test, or how the test is handled by the laboratory may all have an effect. This section covers some of the more commonly seen issues.

Cornell University College of Veterinary Medicine has more information on these factors. Click on the links on the left for more information.

Fasting a Cat or Stopping Fluids Before Tests

If cats are not fasted before blood draws, then lipaemia may occur, particularly if the cat has eaten a meal rich in fat. This means that lipids (fats) are suspended in the blood, which may make the sample thicker and harder to test.

However, lipaemia is relatively rare in feline blood samples, and even if it is present, it is unlikely to make a major difference to the test results. Therefore it is not usually necessary for a cat to fast before the usual tests for CRF, and overall I think it is a bad idea because an empty stomach can increase the risk of stomach acid; plus when they are being fasted, cats simply do not understand why we won't feed them, which is stressful for them, especially if other family cats continue to get fed whilst they do not. However, for certain specialised tests, such as those for parathyroid hormone or pancreatitis, fasting for twelve hours may be necessary; be guided by your vet.

Cornell University College of Veterinary Medicine has more information on lipaemia. Click on Controllable (under Biological) in the links on the left.

Stopping Fluids Before Testing

I have heard of some vets asking that people not give their cats fluids for a day or two (in one case, a week!) before bloodwork. I do not understand this: since the cat normally receives fluids, surely you will obtain more accurate results, reflecting how the cat's bloodwork normally looks, if the cat has his/her usual levels of hydration. But I do recommend that you try to be consistent i.e. always have the tests done before sub-Qs or after sub-Qs, at the same time of day if possible.

Stressed Cats or Cats Who Fight Blood Draws

If your cat fights at the vet, or gets very stressed, this may have an effect on some of the test results. For example, blood glucose levels are often raised in stressed cats, so they do not automatically indicate that diabetes is present. Similarly, CK or CPK, a muscle enzyme, may be raised because of a bad blood draw.

Haemolysis

Occasionally bloodtest results will mention that they are haemolysed. This means the blood cells being tested have ruptured, often as a result of poor handling. Mild haemolysis should not have any real effect, but a grossly haemolysed sample may affect results, causing some values (such as phosphorus) to appear higher than they are and others (such as creatinine) to appear lower. Potassium will usually appear higher than it really is, but occasionally it will appear lower. If a sample has been haemolysed, you might wish to ask your vet to take new blood samples and run the tests again.

Cornell University College of Veterinary Medicine has information on the impact of haemolysis.

BD Tech Talk has more information on haemolysed samples.

Antech also provides information on this issue.

Clumping Platelets

Platelets are the component of blood which causes it to clot. If they were not present, we would bleed to death whenever we got cut. Unfortunately when a sample of blood is taken, some of the platelets may "clump" (stick together), and this is a pretty regular occurrence with feline blood (it is thought to happen in as many as 75% of cat blood draws). It is even more likely if it is difficult to get blood from the cat.

The clumping means that it can be difficult to count the platelets accurately, which in turn means that the number may appear low. However, you may sometimes see platelet counts listed as low, followed by a comment that the platelet estimate is "adequate". This means that the person running the test could not tell the platelets apart enough to be able to count them, but could see that overall there are enough.

If a cat truly has low platelets, then you may see increased bleeding e.g. from the nose, gums or in urine.

Cornell University College of Veterinary Medicine has more information on platelets.

Differences Between US and International Measurement Systems

The USA uses a different measurement system to the rest of the world, which uses the SI system (Système Internationale). If you plan to post your cat’s bloodwork results to the Feline CRF Information list, which has primarily American members, you will therefore need to convert the results to the American system, using this Veterinary Information Network converter. Remember to choose the feline measurements and to enter the SI (international) measurements for conversion to US equivalents, not the other way round. When converting urea from your international results, choose BUN from the dropdown list - that is the nearest US equivalent.

Blood Chemistry Panel:

Measures of Kidney Function

Blood Urea Nitrogen (BUN) or Urea

Blood urea nitrogen is commonly known as BUN in the USA, and, together with creatinine, it is one of the two main measures of kidney function. In the UK, BUN is not normally tested, instead you will see urea listed on your cat's bloodwork. 

Blood urea nitrogen is a measurement of the levels of nitrogen in the blood that come from urea. During the breakdown of dietary protein in the digestive process, ammonia is absorbed in the gut. The liver then makes a substance called urea from the ammonia. The urea is carried in the blood, in the form of urea nitrogen, to the kidneys, which filter it out of the blood and excrete it via urination.

BUN rises in CRF because the kidneys are no longer able to excrete it efficiently; but it can also rise for other reasons, such as dehydration, urethral obstruction (a blockage which prevents a cat from urinating, more common in male cats) or gastro-intestinal bleeding; it is also affected by both diet (since it is a by-product of the breakdown of protein) and stress. 

If BUN and creatinine rise suddenly, you should consider the possibility that your cat has a kidney infection or hypertension. Kidney stones which cause blockages may cause a sudden and high rise in both BUN and creatinine. Cats with a particular form of diabetes called ketoacidosis may also have elevated BUN or urea and creatinine levels, particularly if potassium and phosphorus levels are normal.

Therefore BUN or urea are not an entirely accurate indicator of kidney function, and you should not assume that your cat has CRF based on the BUN or urea measurement alone. However, it is important to try to control high levels of BUN or urea because they can cause lack of appetite, nausea and vomiting. 

If BUN or urea levels are high yet creatinine is normal or only a little elevated, it usually means that the cat is dehydrated, has gastro-intestinal bleeding, or is eating a high protein diet. 

BUN is not normally low in CRF cats, but may be below normal in cats with  liver disease or those who are suffering from starvation. Harpsie once had low BUN levels when he was very sick with an infection (possibly in his liver, though I suspect it was actually a kidney infection) and had not eaten much whilst on IV at the vet's, resulting in rapid weight loss.

The approximate normal levels of BUN or urea for cats are in the table at the end of the page. However, these really are approximate: precise ranges vary from laboratory to laboratory, so you should be guided by the reference ranges which your vet gives you for the particular laboratory which has been used to test your cat. 

Creatinine

Creatinine is another waste product excreted through the kidneys. It is generally considered to be a more accurate measurement of underlying kidney function than BUN or urea because it is less affected by diet, stress and dehydration. In CRF cats, both BUN or urea and creatinine will be elevated to some degree depending upon the severity of the disease; but if BUN or urea levels are high yet creatinine is only a little elevated, it usually means that the cat is dehydrated, has gastro-intestinal bleeding, or is eating a high protein diet. 

Creatinine is not a linear measurement. This means that an increase in creatinine from, say, US 2 to 3, indicates more loss of function than an increase from US 5 to 6. Thus, whilst your cat might have a relatively high creatinine of, say US 5, if it increases to US 6, then whilst you are right to be concerned, it does not automatically indicate a massive worsening of your cat's condition.

See below for information about low creatinine levels in end stage CRF.

Other Reasons for Raised Creatinine

As mentioned above, cats with a particular form of diabetes called ketoacidosis may also have elevated BUN or urea and creatinine levels, particularly if potassium and phosphorus are normal; see Related Diseases for more on diabetes. 

Cats with pancreatitis also sometimes have elevated creatinine levels. If your cat has relatively low creatinine (in the 2s) yet seems lethargic and far more ill than that mild level of kidney failure would suggest, I would consider pancreatitis. I do not cover pancreatitis on this website in detail, but there are links here, and there is more detailed information about it on another website I run, Harpsie's website.

Because creatinine is a by-product of muscle, large, muscular male cats may naturally have high normal levels of creatinine.

An unexpected high prevalence of azotaemia in Birman cats (2002) Gunn-Moore DA, Dodkin SJ & Sparkes AH Journal of Feline Medicine and Surgery 4 pp165-6 (letter) mentions that up to 80% of Birman kittens under six months of age seem to have high levels of creatinine and BUN. As adults, this incidence reduces, but is still high, at 35%. However, in either case these cats do not appear to develop fullblown CRF at a young age as one might expect. Monitoring them regularly would nevertheless be wise.

The effects of cimetidine on renal function in patients with renal failure (1980) Larsson R, Bodemar G, Kagedal B, Walan A, Acta medica Scandinavica 208 (1-2) pp27-31 explains that Tagamet (cimetidine), which is sometimes used to treat stomach acid in CRF cats though it is not the best drug for that purpose, may cause an increase in creatinine. If your cat's creatinine levels rise while using Tagamet, you may find they improve once you stop the medication.

If creatinine and BUN rise suddenly, you should consider the possibility that your cat has a kidney infection or hypertension. Kidney stones which cause blockages may also result in a sudden and high rise in creatinine and BUN.

The approximate normal levels of creatinine (as for BUN or urea, precise ranges vary from laboratory to laboratory) for cats are in the table below. 

BUN:creatinine ratio

If your cat is eating a low protein diet, this ratio is likely to be in the region of 10:1 or 12:1 (e.g. if creatinine is US 4, BUN is likely to be around 40-48). Since BUN is affected by dietary intake, if your cat is eating a higher protein diet, this ratio will be higher, with 18:1 or 20:1 not unusual (e.g. if creatinine is US 4, BUN will be around 80-96).

Severe metabolic acidosis, which affects protein metabolism, may contribute to a high BUN:creatinine ratio. Dehydration also affects this ratio.

Gastro-intestinal bleeding may also cause an increase in the BUN/creatinine ratio (since blood is a form of protein), which needs to be treated if present, since it may cause or worsen anaemia.

If BUN and Phosphorus are High but Creatinine is Low

If BUN (urea) levels and phosphorus levels are high yet creatinine is normal or only a little elevated, it can mean that there is a pre-renal factor at work, for example:

• the cat is dehydrated;

• the cat has gastro-intestinal bleeding (see BUN:creatinine ratio above);

• the cat is eating a high protein diet;

• the cat has severe metabolic acidosis; or

• in some cases it may indicate heart failure.

In end stage CRF, creatinine levels may fall (although this is pretty rare). This occurs because creatinine is a by-product of muscle, and towards the end CRF cats may lose a lot of muscle, and therefore cannot produce as much creatinine. University of Georgia College of Veterinary Medicine explains more about changes in creatinine (scroll down to Variations in Creatinine Concentration).

Azotaemia

Azotaemia is another way of saying that there is increased nitrogenous waste in the bloodstream, i.e. BUN/urea and creatinine levels are elevated. Azotaemia is divided into three stages (bear in mind that blood flows to the kidneys where it is filtered):

• pre-renal azotaemia ("before" the kidney):

  this means that the azotaemia does not involve the kidney and is caused by some other problem before the blood reaches the kidneys, such as infection, fever, a high protein diet, heart problems or dehydration.

• renal azotaemia ("at" the kidney):

  this means the azotaemia is caused at the kidney itself, i.e. CRF or acute renal failure.

   

• post-renal azotaemia ("after" the kidney): 

  this means the increased BUN/urea and creatinine are elevated because of a problem "after" the kidney, i.e. lower down the urinary tract, after the blood has already flowed through the kidneys. A common cause is if a male cat is blocked because of struvite crystals in the bladder, as happened to one of our other cats, Harpsie. The urine cannot flow past the crystals so the cat cannot urinate, and as a result the toxin levels back up in his system and rise in the blood. This is a life-threatening emergency, a cat with this problem needs immediate medical help. Mar Vista Vet has more information on urinary tract blockages.

In order to distinguish between pre-renal and renal azotaemia, urine specific gravity (USG), which is discussed below, needs to be assessed – if USG is above 1.035, then the azotaemia is likely to be pre-renal, if lower than that, it is likely to be renal.

Washington State University College of Veterinary Medicine explains more about azotaemia.

Cornell University College of Veterinary Medicine has information about the different types of azotaemia.

Uraemia

Uraemia means that a cat has azotaemia (increased BUN and creatinine levels) but also has the associated problems commonly seen in CRF patients such as vomiting, increased urination, anaemia etc. You may see reference to uraemic toxins: these are the toxins which the cat's damaged kidneys are unable to filter properly, so they cause many of the symptoms of CRF. One such toxin is parathyroid hormone.

Electrolytes

Electrolytes are salts in the body, which the body needs at cellular level in order to function properly. In CRF, imbalances are quite common.

Potassium

Potassium is used at cellular level, in particular to help muscles function properly. If there is an imbalance, weakness, twitching and seizures may be seen.

Low Potassium Levels (Hypokalaemia)

The increase in urination and vomiting caused by CRF may lead to low levels of potassium, which can have various effects, such as back leg weakness or constipation (see Index of Symptoms and Treatments). Low levels of potassium are known as hypokalaemia.  

Potassium levels may appear to be normal when in fact there is a deficiency. This is because, although potassium is used in the body's cells, the regulatory mechanism of the body is actually set to maintain a certain level of potassium in the blood, not the cells. Thus, when potassium levels drop, as they tend to do in CRF, the cat's body will try to maintain levels of potassium in the blood by taking potassium from the cells. This means that at the intra-cellular level where the potassium is really needed, potassium levels are too low, even though the blood levels of potassium may appear to be normal. One study, Feline renal failure: questions, answers, questions (1992) Lulich JP, Osborne CA, O’Brien TD and Polzin DJ Compendium on Continuing Education for the Practising Veterinarian 14 pp127-153) estimated that approximately 30% of CRF cats have low potassium levels.

In addition, if a cat has metabolic acidosis, the potassium level may appear normal or high in blood tests, but may subsequently fall after the metabolic acidosis is treated. It is very important to treat both conditions because, according to Dr David Polzin, "potassium depletion and metabolic acidosis may promote potentially fatal reductions in plasma taurine concentrations in cats."

Because of this, and since there is no way of measuring levels of potassium in the cells, many vets supplement potassium in CRF cats when it falls below the middle of normal, usually about 4.4 mmol/L/l (US: 4.4 mg/dl). The reason for this is that if it is impossible to raise the levels in the blood to the middle of normal, it must be because the cells are depleted to such an extent that they cannot release any more potassium into the blood. Therefore, if your cat's bloodtests show a low-normal level of potassium, it is worth discussing the use of a supplement with your vet. Ways to increase potassium levels can be found in Treatments. 

Cats with diabetes may also have low potassium levels. Very occasionally, low potassium levels may be caused by a condition known as hyperaldosteronism, but this is very rare in cats. If hyperaldosteronism is present, the cat will often also have high sodium levels, and will frequently develop hypertension. Less common feline endocrinopathies (2004) is a presentation by BR Jones to the World Small Animal Association World Congress 2004. Scroll to the last section for information on hyperaldosteronism.

Do not supplement potassium without your vet's knowledge and approval, because not all CRF cats have low potassium levels, and giving potassium to a cat who does not need it can be very dangerous.

Penn State University College of Medicine has some information on low potassium levels in humans.

High Potassium Levels (Hyperkalaemia)

It is important to understand that not all CRF cats need potassium supplements. Some cats never have low potassium levels, particularly if their CRF is relatively advanced (creatinine over 5). Thomas's creatinine was not that high, yet he never needed potassium, and the same study as mentioned above (Lulich et al., 1992) found that around 13% of CRF cats actually have the opposite problem of hyperkalaemia (high potassium levels). Therefore you should not supplement potassium without a bloodtest and your vet's approval.

If your cat has high potassium levels, (over 6), this is potentially very dangerous, and may cause seizures and even a heart attack. See Treatments for how to handle high potassium levels.

Cornell University College of Veterinary Medicine has some information on hyperkalaemia. 

Sodium

Sodium is excreted by the kidneys, but levels may rise in CRF cats because the kidneys are no longer working as efficiently and cannot adapt to changes in sodium levels as quickly. It is important to monitor sodium because high levels can worsen hypertension (high blood pressure).

Magnesium

For some reason, magnesium is only rarely measured during routine blood tests. In CRF cats, magnesium levels tend if anything to be high, because the damaged kidneys cannot excrete it properly. Therefore CRF cats do not normally need a magnesium supplement. This is one reason why using phosphorus binders containing magnesium is also not recommended.

Occasionally, however, a CRF cat will have low magnesium levels. Usually such a cat will also have low potassium levels, and both potassium and magnesium will return to normal once a potassium supplement is begun. If, however, your cat has low potassium levels which do not rise despite the use of a potassium supplement, it is possible that the low magnesium also needs to be treated. In such cases, you are unlikely to be able to raise the potassium to an acceptable level until you have also treated the low magnesium. Your vet should also consider the possibility of hyperaldosteronism if your cat has persistently low levels of magnesium and potassium, especially if hypertension is also present. 

Metabolic Acidosis

 

Arterial Blood Gas

TCO2 or CO2

Anion Gap

In healthy cats, acids resulting from the cat's diet are flushed from the body by the kidneys; the kidneys also reabsorb bicarbonate, a body chemical which in normal cats acts as a "buffer" for acid levels. However, both of these mechanisms are often damaged in CRF cats, so acidity levels in the body rise (i.e. the body’s pH becomes too low) – this is known as acidosis, and can cause muscle wasting, partly because acidosis prevents the cat's body from metabolising protein properly. "Metabolic" means that the acidosis is not caused by the lungs (which may cause another type of acidosis called respiratory acidosis if they do not expel carbon dioxide properly), but by kidney failure.

One study, Assessment of acid-base status of cats with naturally occurring chronic renal failure (2003) Elliott J, Syme HM, Reubens E & Markwell PJ Journal of Small Animal Practice 44(2) pp65-70, found that metabolic acidosis generally does not occur until the CRF is relatively advanced, but I know some cats on the Feline CRF Information list have had metabolic acidosis even with pretty low creatinine levels, and this was also the case with one cat in a study, Acid-base balance of cats with chronic renal failure: effect of deterioration in renal function (2003) Elliott J, Syme HM, Markwell PJ Journal of Small Animal Practice 44(6) pp261-8. Therefore it is important to be aware of the need to monitor for this - many vets do not watch for metabolic acidosis routinely.

Blood Gas Analysis

This is the most accurate way of testing for metabolic acidosis, but it's very hard to find a place where this test can be done.

TCO2

Some vets diagnose metabolic acidosis from the pH levels of the urine, but TCO2 or total carbon dioxide in the blood is a more accurate way of measuring levels of bicarbonate. If TCO2 is low, it can be a sign that the blood's protective bicarbonate levels are depleted from too much acid. However, TCO2 has to be measured on a special blood gas machine, which not many vets and not all laboratories have. It is also easy to make mistakes in taking the measurement because if the sample is exposed to air, the dissolved gas escapes and makes the reading look lower than it really is. As a result, some laboratories may use a range with a very low minimum level to allow for this possibility; but the usual range is about 17 to 23. It is usually worth starting treatment if the level is below 16.

Not all laboratories measure TCO2, or some, such as Antech in the USA, may only measure it on request because of the problems in taking the measurement (with Antech, you need to follow their instructions in the above link and ask for Test No. T115). If your vet or his/her laboratory cannot measure TCO2 at all, it is worth asking your vet if it is possible to test for carbon dioxide (CO2) levels instead - if they are low, they may also indicate metabolic acidosis. 

Metabolic acidosis must be treated if present, because it can have a variety of effects, see Symptoms and Treatments. In addition, if a cat has metabolic acidosis, the cat's potassium levels may appear high or normal in blood tests, but may subsequently fall after the metabolic acidosis is treated; if  hypokalaemia (low potassium levels) results, this must be treated. It is also very important to treat both conditions because, according to Dr David Polzin, "potassium depletion and metabolic acidosis may promote potentially fatal reductions in plasma taurine concentrations in cats."

Anion Gap

This is the difference between measured concentrations of cations and anions in the blood. It is calculated as follows: AG = [Na+ + K+] - [Cl- + HCO3]  which in English means: anion gap = [sodium + potassium] – [chloride + bicarbonate]. Medical College of Wisconsin will calculate it for you if you input the appropriate values from your cat’s bloodwork. 

The normal range for cats is around 10-27, though it does vary greatly from lab to lab. If the anion gap is increased in a CRF cat, it may indicate metabolic acidosis, so if your vet is unable to test TCO2 or CO2, but has checked the anion gap, this may be an indicator (although you need to be aware that there are other causes of metabolic acidosis too which may not be reflected in the anion gap). 

This topic is rather complex but here are some links for more information:

Acid-base management of the CRF cat (2004) is a helpful overview by Dr JW Bartges of the University of Tennessee College of Veterinary Medicine.

Acid-base balance: an overview (2007) Morse H, Webb JL & LeRoy BE is a paper from the University of Georgia College of Veterinary Medicine.

Cornell University College of Veterinary Medicine - lots of detailed information on metabolic acidosis and the anion gap.

Veterinary Information Network - Dr Katherine James’ pages on acid base disturbances.

Acid-base, electrolytes and renal failure (1999) Polzin DJ, Osbourne CA, James K Supplement to Compendium on Continuing Education for the Practising Veterinarian 21 11(K)) has information on metabolic acidosis and CRF.

Minerals

Secondary Hyperparathyroidism

This is a complex subject, and not to be confused with hyperthyroidism. It is caused by part of the body's mechanism for controlling phosphorus and calcium levels effectively going into overdrive. One study, Feline chronic renal failure: calcium homeostasis in 80 cases diagnosed between 1992 and 1995 (1998) Barber PJ, Elliott J Journal of Small Animal Practice 39 pp108-116), found that 84% of the cats in the study eventually developed this problem, so it is important to be aware of the possibility.

Parathyroid Hormone

Glands called the parathyroid glands control the levels of phosphorus and calcium in the body. In healthy cats, if phosphorus levels are too high, or if calcium levels are too low, the levels of ionised calcium in the body fall. The parathyroid glands are then stimulated to produce more of a hormone called parathyroid hormone (PTH), which tries to adjust the levels of calcium and phosphorus to their correct levels, partly by taking calcium from the bone and by increasing the passing of phosphorus in the urine. It also stimulates the synthesis of calcitriol as the major mechanism to increase levels of blood ionised calcium.

This mechanism should cease once levels of ionised calcium have been restored because calcitriol can normally stop the secretion of PTH; however, as kidney function reduces and calcitriol is not synthesised in adequate amounts, this mechanism may no longer work properly: phosphorus levels may continue to increase and to block calcitriol synthesis and also block dosed calcitriol's ability to regulate PTH gene transcription, and thus stimulate PTH levels to continue rising. Blood calcium levels may appear normal but eventually various symptoms may appear, including lack of appetite (blood glucose levels rise which stop the cat feeling hungry), anaemia, reduced immunity to infection and muscle weakness. If phosphorus multiplied by total calcium is higher than 60-70, the cat is at risk of tissue calcification. Washington State University College of Veterinary Medicine has information on this (scroll down to "Calcium levels").

One possible treatment (although some vets are opposed to it) for secondary hyperparathyroidism is to give CRF cats calcitriol. There is more information on this in the Treatments section. However, this treatment is not currently available in the UK, because the calcitriol needs to be compounded, which is not legal in the UK.

Endocrine Web - a human site but has a lot of information.

Mar Vista Vet - has information on calcitriol.

Michigan State University can run a test to check ionised calcium levels if required. They also have a helpful explanation of why ionised calcium is important.

Phosphorus (P or Pi)

CRF kidneys can no longer excrete phosphorus properly so levels rise. It is important to treat excess phosphorus (hyperphosphataemia) because it can adversely affect calcium levels, with potentially serious consequences (see parathyroid hormone below), and can generally make the CRF progress faster. Your cat may appear to have phosphorus levels within normal limits, but bear in mind that normal limits apply to all cats, young and old, healthy and ill: Dr Katherine James of the Veterinary Information Network, and Dr Larry Nagode of Ohio State University strongly recommend actively aiming to keep phosphorus under control once it goes above 1.9 mmol/L/l (US: 6 mg/dl), with a view to getting it to a level of 1.3 mmol/L/l (US: 4 mg/dl) in a CRF cat. Ways to reduce phosphorus levels can be found in Treatments. 

Low phosphorus levels are not normally present in CRF cats, but are generally not considered to be a problem in any cat.

Calcium

Calcium is necessary for nerve function, muscle contraction, blood clotting, and the skeleton. CRF cats can have too little calcium (hypocalcaemia) or too much (hypercalcaemia). 

High Calcium Levels (Hypercalcaemia)

The normal level of calcium in the blood is in ratio to the phosphorus level - calcium levels are usually at an approximate level of 100 - 200% of phosphorus levels. Thus, if phosphorus levels are high, calcium levels may also rise in an attempt to maintain the ratio; conversely, if the phosphorus level is reduced, often the calcium level will reduce to a satisfactory level. 

Metabolic acidosis may also contribute to hypercalcaemia, since acid in the blood leads to the release of calcium from proteins or from bone. 

High calcium levels may contribute to constipation; and conversely some people have found that using lactulose to control constipation has led to hypercalcaemia in their cats. You may therefore wish to avoid this treatment if your cat already has hypercalcaemia, and consider alternative treatments if your cat has developed hypercalcaemia since beginning lactulose. The Treatments page has more information on this problem and on alternative treatments for constipation.

Occasionally, high calcium levels may be a sign of cancer.

On 6 March 2006, Royal Canin began recalling its renal LP food sold in pouches in the USA because of an excessive amount of Vitamin D in the food. This apparently caused hypercalcaemia in four cats to date.

Calcium exists in three different forms in the body, but the measurement which is important is ionised calcium (which forms about 50% of total calcium), because only ionised calcium is metabolically active. If total calcium is high, it is worth asking your vet if ionised calcium can be checked (although not all laboratories can do this): if ionised calcium is normal, there is no need to worry.

If calcium goes above 15 mg/dl, a cat may have little appetite and sleep a lot; if levels approach 20 mg/dl the cat may go into a coma and die. However, such levels are extremely high and in practice you are unlikely to see them. But high levels of calcium are also likely to trigger calcification (see parathyroid hormone). See Treatments for how to treat hypercalcaemia.

Diagnostic tree: elevations in total serum calcium (2007) Fan TM NAVC Clinician's Brief May 2007 pp30-31 presents the possible causes of elevated calcium in flow chart format.

Antech Diagnostics has information on hypercalcaemia from Dr Dennis Chew written in 2000.

Hypercalcaemia in cats (2001) is a paper by Dr Chew presented to the World Small Animal Veterinary Association World Congress 2001 .

Vetcentric discusses common causes of hypercalcaemia.

Veterinary Partner has a good overview of hypercalcaemia.

Hypercalcemia in dogs and cats: etiology and diagnostic approach (2002) is a paper presented to the 27th World Small Animal Veterinary Association Congress 2002 by Richard Nelson. 

Michigan State University can run a test to check ionised calcium levels if required. They also have a helpful explanation of why ionised calcium is important (go to No. 2).

Low Calcium Levels (Hypocalcaemia)

Calcitriol (1,25 dihydroxycholecalciferol) is the active form of Vitamin D3, and,  despite its name, is actually a hormone. It is necessary for the absorption of calcium from the gastro-intestinal tract and to help the release of calcium from the bones where it is stored.  Cats have to make calcitriol from Vitamin D before they are able to use it, and the final step of this process is a function performed by the kidneys. 

Because of their failing kidneys, CRF cats may no longer be able to convert vitamin D into calcitriol, so they absorb less calcium from the gastro-intestinal tract and release less from the bones, and thus levels of calcium in the body may fall. Excess phosphorus can also reduce calcium levels by suppressing the production of calcitriol. Treatments has information on dealing with hypocalcaemia.

Total Protein (Proteins in the Blood)

Total Protein (TP)

Total protein is the sum of the two proteins in the blood, albumin and globulins (see below). High total protein levels may be seen when a cat is dehydrated. In this case, albumin will probably also be high.

Albumin (Alb)

This is the main protein in blood. Albumin may be high or low:

High Albumin

If albumin is high, it may indicate dehydration. In this case, total protein will probably also be high.

Low Albumin

Albumin may be low in a cat with gastro-intestinal bleeding or some other kind of problem which causes inadequate nutrition. Cats with a chronic infection or chronic inflammation, such as cats with Inflammatory Bowel Disease (IBD), may have low albumin and total protein levels, as may cats with liver disease. Nephrotic syndrome will often cause low albumin levels, but this syndrome is quite rare in cats.

One of albumin's roles is to provide pressure to keep water in the blood, so if it falls too low, there is a greater risk of fluid build up (oedema or ascites). This can sometimes happen if your cat is being overhydrated.

If your cat's albumin level is very low (below 2 US, 20 international), please discuss this with your vet, because it can be quite dangerous.

If albumin is low, usually calcium will also be low. 

Cornell University College of Veterinary Medicine has some information on albumin.

Health A to Z explains more about ascites.

Globulin

This is another protein in blood, and is calculated from the values for albumin and total proteins i.e. globulin = total protein minus albumin. Globulins contain antibodies (immunoglobulins), so high levels may be seen when infection or inflammation is present.

Cornell University College of Veterinary Medicine has information on globulins.

Albumin:Globulin Ratio

This is as it suggests, the ratio between albumin and globulin. It should normally be 1:1. If the ratio is lower than this, then globulins are high. If the ratio is higher than this, then albumin levels are high. A high total protein with a normal A:G shows dehydration.

Other Bloodwork Which May Be Out of Range

Creatine Kinase (CK) and Creatine Phosphokinase (CPK)

These are two slightly different names for the same muscle enzyme, which is released when muscle is damaged. The US laboratory, Antech, mentions that this value can also increase in anorexic cats.

In most CRF cats, there is usually only a mild increase if any, and this might simply be because of the stress of being held and having blood taken at the vet’s; occasionally, levels also increase after prolonged inactivity or if a cat has a seizure. Many labs have a maximum level of 300, and a level of up to 500 is not usually cause for concern.

If levels are high, it may indicate some kind of muscle disease; alternatively, very high levels of CK are often seen when an animal has heart issues. If your cat's level is over 1800, your vet should investigate further.

Cornell University College of Veterinary Medicine has some information about CK levels.

Cholesterol (Chol)

High cholesterol levels do not have the same significance for cats as they do for humans, but are usually secondary to some other disease, e.g. cats with thyroid problems may have high cholesterol levels. As in humans, bloodwork results will vary depending upon whether the blood is taken after fasting. It is not uncommon for CRF cats to also have increased cholesterol levels. Occasionally, high cholesterol levels are seen in cats with nephrotic syndrome, but this syndrome is quite rare in cats.

Cornell University College of Veterinary Medicine has some information about cholesterol levels.

Glucose (Glu)

This is also known as blood sugar. This value may increase suddenly because of stress – it is not uncommon for this value to be high in cats who get stressed or frightened at the vet’s. Therefore a high level on one occasion should not be taken to indicate diabetes, urine testing is also required. Please note that glucose levels may rise in cats with secondary hyperparathyroidism.

Cornell University College of Veterinary Medicine has some information on glucose and mentions here that stress may make glucose levels rise in cats.

ALT (Alanine Aminotransferase) or SGPT (serum glutamic-pyruvic transferase)

This is an enzyme which is largely found in muscle, the liver and the brain. It often leaks out of damaged liver cells, so is an indicator of liver disease, although it is sometimes elevated in hyperthyroidism. Cats on methimazole for hyperthyroidism may also have elevated liver enzymes and low white blood cells. Mild elevations are not normally cause for concern - one of my cats has mildly elevated ALT for years without problems. If a sample is haemolysed, ALT may be elevated.

Cornell University College of Veterinary Medicine has some information about ALT.

Amylase (Amyl)

Amylase is a digestive enzyme made in the pancreas that breaks carbohydrates down into simple sugars. Because amylase is made by the pancreas, many vets seem to assume that an increase in this enzyme must indicate pancreatitis. Whilst this is often true for other species, it does not usually apply to cats, particularly CRF cats, because amylase is excreted by the kidneys, so it is by no means uncommon for it to be elevated in CRF. This is not usually a cause for concern - a value up to 2200 is not uncommon in CRF cats. However, if the level is much higher, around three times normal level, and your cat is showing other symptoms of pancreatitis combined with relatively low CRF values that seem to be out of line with how ill your cat is acting, then you might want to rule it out.

B.  Complete Blood Count: Anaemia and Infections

A complete blood count, also known as haematology, examines the blood cells in the body. The blood count is most helpful in determining firstly, whether a cat is anaemic, and secondly, whether a cat has an infection.

Pet Education has information about the complete blood count and what it means.

Signs of Anaemia

Anaemia is relatively common in CRF, because the kidneys produce a hormone called erythropoietin, which stimulates the bone marrow to make red blood cells; but damaged CRF kidneys may no longer perform this task properly. In addition, a uraemic toxin called parathyroid hormone, which is not processed properly by damaged kidneys, may also adversely affect the production of erythropoietin. And finally the lifespan of red blood cells in renal failure patients is approximately 50% that of healthy cats.

There are two classes of anaemia, regenerative and non-regenerative, with the latter being more common in CRF cats and usually linked to the CRF. The following are some of the values from the complete blood count which will tell you more about your cat's anaemia and whether it is regenerative or non-regenerative.

Packed Cell Volume (PCV) or Haematocrit (HCT)

This is a measurement of anaemia. PCV is sometimes referred to as haematocrit or HCT, although they are not quite the same thing. Packed Cell Volume (PCV) measures the ratio of red blood cells to total blood volume. The blood is spun in a centrifugal machine and your vet measures the total number of cells that are left. Haematocrit (HCT) actually refers to the red cells that are left only; but since the other blood cells (white cells and platelets) usually make up less than 1% of blood volume, the difference between PCV and HCT is too small to be concerned about. Only a small amount of blood is needed for these tests (although more blood is needed for HCT than for PCV) and many vets have the necessary equipment in their offices so you can get a result in a few minutes. Technically, a cat is anaemic if his/her PCV level is below 30% (or with some labs, 25%), but you may not start to see any differences in your cat's behaviour until the level is closer to 20%. Dehydration will make PCV look higher than it really is, so once a cat is rehydrated, PCV will often have fallen.

This is a measure of red blood cell size. If your cat has a low MCV, this may indicate a lack of iron (which can cause anaemia), or in some cases chronic liver disease. 

Cornell University College of Veterinary Medicine has more information about MCV.

Red Blood Cells (RBC)

If a cat cannot manufacture sufficient red blood cells, s/he will become anaemic. Unfortunately the lifespan of red blood cells in renal failure patients is approximately 50% that of healthy cats, so this is another reason why CRF cats become anaemic.

A low red blood cell count is usually indicative of anaemia. 

If the RBC count is high, this may be indicative of dehydration.

Reticulocytes

The PCV test shows if your cat is anaemic, but it does not show whether the anaemia is regenerative or non-regenerative. The only way to know for certain which type of anaemia you are dealing with is by testing for reticulocytes; but this cannot be done unless the anaemia is already severe. 

Reticulocytes are immature red blood cells. Since anaemia means there is a lack of red blood cells, the body's usual response is to try to generate more red blood cells, so normally you would see reticulocytes if the anaemia is regenerative - this shows that the bone marrow is still making blood cells. However, in non-regenerative anaemia (as often seen in CRF), the lack of erythropoietin means the bone marrow is not able to make blood cells, or not enough of them to replace old ones, so there will be few or no reticulocytes present. 

It should be noted that the reticulocyte test is unlikely to be reliable unless the anaemia is moderate to severe - anaemia needs to be fairly bad before a brisk regenerative response is considered necessary by the cat's body - so there is no point in testing for reticulocytes unless the PCV is below 20%. If the reticulocyte count is still low or zero despite the PCV being below 20% (at which stage of anaemia, the bone marrow would normally be busy making new red blood cells if it could), this indicates non-regenerative anaemia.

Since there is no point in measuring reticulocytes until PCV is below 20%, and since anaemia in a CRF cat is likely to be of the non-regenerative kind caused by the failing kidneys, many vets simply assume that a CRF cat with anaemia is suffering from non-regenerative anaemia and treat accordingly. Whatever the cause, it is very important to treat anaemia if it is present - left untreated, it will probably kill a cat before the CRF does. See the Anaemia page for more information on anaemia and how to treat it

Cornell University College of Veterinary Medicine provides more information on this complex subject: click on the word Feline on the left of the page for further information, including a table of reticulocyte counts.

Antech Diagnostics have information on how they run the reticulocyte test.

Idexx Laboratories have some information on reticulocytes.

Signs of Infection

White Blood Cells (CBC)

White blood cells, sometimes called leukocytes, are the body's defence system. If inflammation or infection are present anywhere in the body, white blood cells will accumulate there to fight the invaders, and therefore the total number of white blood cells will increase.

There can be other causes of increased white blood cells, such as the use of corticosteroids or if the cat is stressed, e.g. if a cat fights during a blood draw. WBCs are often very high in cases of acute renal failure.

In contrast, cats on methimazole for hyperthyroidism may have low white blood cells.

There are four main types of white blood cells, divided into two groups:

Granulocytes:

• neutrophils

• eosinophils

Agranuloctyes:

• lymphocytes

• monocytes

There are also basophils but these are only rarely seen.

In order to work out where the problem lies, it is necessary to differentiate between how many of each type of WBC there are. This is called the differential count, and it usually shows two sets of numbers: the actual amount of each type of WBC (abbreviated as absolute or ABS); and the percentage of each type.

Pet Place has a good overview of WBCs.

Cornell University College of Veterinary Medicine explains more about WBCs.

Neutrophils

Neutrophils are the most numerous white blood cell. They are produced in the bone marrow. High neutrophils usually indicate the body is fighting a bacterial infection, though sometimes levels are high because of stress or inflammation.

Mature neutrophils are called segs (segmented cells) whilst immature ones are called bands. If a bacterial infection is present, more bands are released into the blood than would normally be the case to help fight it, so the percentage of bands increases compared to segs (sometimes called "a shift to the left"). The higher the number of bands, the more severe the infection.

In contrast, neutrophils are often low in cases of viral infection. They may also be low in cases of severe inflammation or bacterial infection where the body has struggled to keep up with the demand for them. Cats lacking Vitamin B12 and/or folic acid may have low neutrophil levels.

If a cat undergoes a stressful blood draw, the test results may show a high neutrophil count (an increase in segs rather than bands) with a low lymphocyte count; in such cases, you might also see elevated CK levels.

Bio Chem Web has a great video of a neutrophil hunting a bacterium.

Cornell University College nf Veterinary Medicine has some information about segs.

Cornell University College of Veterinary Medicine also has some information about bands.

Eosinophils

Eosinophils are also produced in the bone marrow. Levels are often high because of acute or chronic inflammation e.g. that caused by IBD, asthma or allergies. I have many allergies plus asthma, and I always have high eosinophil levels. Other possible causes include parasites and occasionally lymphoma, a type of cancer.

Cats on steroids may have low eosinophil levels. Cats with acute or chronic inflammation or infection may also have low eosinophil levels.

Cornell University College of Veterinary Medicine has some information about eosinophils.

Lymphocytes

As the name suggests, lymphocytes are produced by the lymph glands, and also by the spleen. They consist of B cells and T cells. B cells work by producing antibodies which neutralise the threat, T cells work with other cells to do the same thing.

Lymphocytes are often low in cases of viral infection or when using steroids. They may also be low in cases of chronic bacterial infections. CRF cats with uraemia (which tends to apply to most CRF cats) often have low lymphocytes, as may cats on steroids. Lymphocytes may be increased in cases of chronic infection or inflammation, autoimmune disease or leukaemia (cancer of the blood). Cats taking medications for hyperthyroidism may also have elevated lymphocyte levels.

If a cat undergoes a stressful blood draw, the test results may show a high neutrophil count (an increase in segs rather than bands) with a low lymphocyte count; in such cases, you might also see elevated CK levels.

Cornell University College of Veterinary Medicine has some information about lymphocytes.

Monocytes

Monocytes can be produced in either the bone marrow or the spleen. They are capable of leaving the blood stream to enter surrounding tissues in order to reach hostile bacteria. They also remove damaged body cells, so are often present when there is tissue necrosis (dying tissue). Their numbers do not usually vary much unless leukaemia (cancer of the blood) is present.

Cornell University College of Veterinary Medicine has some information about monocytes.

Urine pH

This is a measure of the acidity/alkalinity of urine. A normal level is in the range of 6.0 - 6.5. A cat with a urine pH higher than this (i.e. more alkaline urine) can be at risk of developing struvite crystals, and a cat with urine pH lower than this (i.e. more acidic urine) can be at risk of developing calcium oxalate stones.

Pet Education mentions that normal pH for cats is 6 - 6.5.

Osmolality

This is a measure of particles dissolved in solution. Urine osmolality measures the concentration of the urine. Serum (blood) measurement of osmolality gives some indication of hydration levels - a dehydrated cat will often have high osmolality, while an over-hydrated cat will usually have low levels. High levels may also indicate azotaemia. Normal range for urine osmolality is 270-320.

Cornell University College of Veterinary Medicine has more information about USG and osmolality. 

Rnceus.com is a human nursing site with some information on osmolality.

Washington State University College of Veterinary Medicine explains how the method of collecting the urine is important, because this may influence the level of protein found therein.

In New news for feline chronic renal failure (2004) Elliott J Waltham Feline Medical Symposium presented to the 2004 North American Veterinary Conference, Dr Jonathan Elliott discusses the importance of protein in the urine as a risk factor for the development of CRF. He states that the urine protein:creatinine ratio should be calculated: <0.5 is non-proteinuric; between 0.5 and 1.0 is borderline proteinuric; and over 1.0 is proteinuric.

The Pet Check Up is a similar test that checks for blood in urine, and which may also be used to check for other issues, such as diabetes.

Health Meter Cat Litter can detect blood in urine, and also checks urine pH. 

Most vets use what is called indirect blood measuring equipment, which is wrapped around the cat's tail, rather like the equipment used on a human's arm to measure blood pressure. The usual type is Doppler equipment, and with a Doppler, only the systolic pressure is measured. 

Unfortunately not all vets  have the equipment with which to check blood pressure. Your vet can do certain checks in the surgery for signs of high blood pressure, such as checking the pupils, heart rate etc., though it is not possible to obtain an accurate measure of blood pressure using these methods. You could encourage your vet to buy the necessary equipment, which can be obtained relatively cheaply (US$600-1000 in the USA, £400-600 in the UK). Some people with CRF cats have purchased blood pressure monitoring equipment for home use, and been trained in its use by their vet; this is not only more convenient, but it also avoids the problem of "white coat syndrome", where a cat's blood pressure appears to be higher than it is because of the stress of being at the vet's.

Blood pressure measuring equipment which can be purchased for home use:

Parks Medical (model no. 811) is a popular brand which has been used by a number people dealing with CRF over the years. You do need a vet's prescription to buy one.

Vmed Vet Dop Doppler is another brand which several people with CRF cats have purchased recently. With all the extras, it costs about US$1000.

Burtons in the UK sells the 811 Parks model, but does not give a price, and it looks like you would have to have your vet order it on your behalf.

Thames Medical (click on Doppler) shows a cat having blood pressure checked.

Washington State University College of Veterinary Medicine has more information on hypertension, including pictures of blood pressure monitors. Scroll down to hypertension.

Washington State University College of Veterinary Medicine has more information on hypertension, including pictures of blood pressure monitors. Scroll down to hypertension.

D.  Other Diagnostic Tests

You might like to read Causes of CRF to understand more particularly what might be affecting your cat's kidneys. However, CRF is primarily a disease of older cats; and often it is either impossible to know what has caused it, or it doesn't really matter because by the time of diagnosis it is irreversible. For young cats with CRF or for cats where an obvious cause is suspected, your vet might want to run some of the following tests. 

Renomegaly (Enlarged Kidneys)

As mentioned above, most CRF cats have small, scarred kidneys. However this is not always the case. Cats with a disease called Polycystic Kidney Disease or PKD (see Related Diseases) usually have large, swollen kidneys. Cats with renal lymphoma, a form of cancer, may also have large kidneys, as may cats with perinephric pseudocysts. Another condition called hydronephrosis may cause enlargement of the kidneys with urine because of obstruction of the ureter, which prevents urine from passing through. Cats with acute renal failure may have enlarged kidneys.

Occasionally a cat will have one small kidney and one large kidney, a condition known with startling originality as "big kidney little kidney syndrome". This is commonly caused by stones or obstructions. 

Palpation of Kidneys

The first thing your vet will do is usually a physical examination of the kidneys by palpating (feeling and moving) them through the skin. This will tell your vet whether the kidneys feel small or large (renomegaly) and he/she may also be able to feel scar tissue, although kidney palpation alone is not sufficient for a diagnosis. Most CRF cats, though by no means all, have small, scarred kidneys.

If you suspect that your cat has gastro-intestinal bleeding, you should take a stool sample to your vet for testing and ask for an occult blood test. You can also buy the EZ Detect test from pharmacies, which tests for blood in the stool or urine (this is a human test but can also be used for cats).