Occult Blood Test For Gastrointestinal Bleeding

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Home > Diagnosis > Other Diagnostic Tests



  • CKD is normally diagnosed via blood tests and urinalysis (urine tests).

  • Sometimes other tests may be appropriate, for example, if a kidney infection is suspected, or if a young cat has CKD.

  • The tests below are listed in order of invasiveness.

Occult Blood Test for Gastrointestinal Bleeding


This test is the least invasive, because initially it does not require that you take your cat to the vet.


If you suspect that your cat has gastrointestinal bleeding (which could be the case if your cat's BUN:creatinine ratio is high, PCV or HCT is falling and albumin and/or the MCV are low), you should take a stool sample to your vet for testing and ask for an occult blood test. 


I did this test when Ollie was anaemic. My vet had never been asked to do this test before, but Ollie's test was positive.


You can 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). You can drop some of your cat's stool in the toilet and then follow the instructions on the packet.


Do not give iron supplements for a couple of days before obtaining a sample for testing. Ideally you should also feed no red meat products beforehand, because red meat may give a false positive. I was reluctant to restrict Ollie's diet because he was already anaemic and not eating too well, but Ollie seemed to do well enough on chicken-based foods. Do check what you are feeding though, many commercial foods contain more than one meat source.


VCA Animal Hospitals discuss the faecal occult blood test.


Effect of dietary factors on the detection of fecal occult blood in cats (2001) Tuffli SP, Gaschen F & Neiger R Journal of Veterinary Diagnostic Investigation 13(2) pp177-9 explains more about dietary restrictions and concludes "Both tested kits are clinically useful for occult blood in cat feces; however, the diet fed prior to testing must be taken into consideration, and dietary restrictions are advisable before testing."


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 CKD cats, though by no means all, have small, scarred kidneys.


Oral Checks


Many cats with CKD have dental problems, which in some cases may even have contributed to the development of CKD.  It is therefore important for your vet to keep a close eye on your cat's mouth and to treat any dental disease, and also to look for mouth ulcers. Most vets will examine your cat's mouth routinely at visits, but many dental problems are invisible to the naked eye.


There is a page devoted to dental problems.




Ultrasounds can be performed on various parts of the body, usually the heart, abdomen or kidneys.


In terms of kidneys, an ultrasound allows the vet to examine the kidneys to check their size and to look for certain abnormalities in their shape or form. It normally looks at the following parts of the kidneys:

  • renal cortex: the outer part of the kidneys

  • renal medulla: the innermost part of the kidneys

  • renal sinus: the main cavity of the kidneys, which contains the renal pelvis, amongst other things

The renal pelvis is the top of the ureters (the tubes that lead to the bladder). It is not always looked at on ultrasound, though it can be helpful for some diagnoses.


Ultrasounds are not invasive and can usually be done without anaesthesia or even sedation, so there is no need to fast the cat beforehand. The cat may need to be shaved at the examination site (although my extremely fluffy Chinchilla had a cardiac ultrasound without being shaved). Cold gel has to be applied to the body to allow the equipment to work properly, which may be a little uncomfortable when first applied (ask if you can warm it a little in your hands first), but all my cats who have had ultrasounds coped just fine.


Pilot study to evaluate the potential use of the renal resistive index as a preliminary diagnostic tool for chronic kidney disease in cats (2017) Matos I, Azevedo P & Carreira LM Journal of Feline Medicine and Surgery 19 epub looked at using ultrasound to assess the use of the renal resistive index to help diagnose in CKD cats. The study found "No differences were found for the RRI between the left and right kidneys, suggesting that evaluation of only one kidney is sufficient to provide an estimate of the RRI value for both organs. RRI measurement, which can be achieved with CDUS [colour doppler ultrasound], is an easy-to-use diagnostic tool that, with a cut-off value of 0.639 for both kidneys, is useful in establishing a preliminary diagnosis of CKD."


Long Beach Animal Hospital has information on ultrasounds.


Pet Place explains more about abdominal ultrasounds.


Renal imaging in cats (2008) Seyrek-Intas D & Kramer M Veterinary Focus 18(2) pp23-30 discusses ultrasounds.


Ultrasound: When to Use

Ultrasounds should always be considered for diagnosing:

Ultrasounds are unlikely to be worthwhile for the diagnosis of CKD. Ultrasound of cats with chronic renal disease (2007) Zwingenberger A Veterinary Radiology says ""Although ultrasound is able to detect changes in chronic renal disease, it is not highly sensitive. Cats can have significant renal dysfunction without ultrasonographic signs of renal disease. Conversely, many cats cope with their chronic renal disease though they have severe ultrasonographic changes. The history and bloodwork are important in assessing the significance of the findings."


Having said that, recent research indicates that all CKD cats could benefit from an ultrasound at initial diagnosis. Renal pelvic and ureteral ultrasonographic characteristics of cats with chronic kidney disease in comparison with normal cats, and cats with pyelonephritis or ureteral obstruction (2017) Quimby JM, Dowers K, Herndon AK, Randall EK Journal of Feline Medicine & Surgery 19(8) pp784-790 found that the renal pelvis could be dilated in cats with CKD, as well as in cats with pyelonephritis and kidney stones and states "these data suggest CKD cats should have a baseline ultrasonography performed so that abnormalities documented during a renal crisis can be better interpreted."


Therefore, if you can afford it, I would consider an ultrasound when your cat is first diagnosed.


Ultrasound: Who to Use

You need a competent and experienced person to perform the ultrasound, ideally a radiologist. What you should know about your pet's ultrasound exam (2009) Murray L Vet Confidential states ""If your pet ever needs an ultrasound exam, it's crucial to ensure that it's done properly. An inadequate ultrasound can be worse than none at all, since it often leads to misdiagnosis, which can be very dangerous for your pet. The use of ultrasound in veterinary medicine has become very common but there are no regulations in place to ensure that your petís ultrasound is performed competently."


Sometimes you may be offered the option to have the ultrasound performed by your vet who will then send the images to a radiologist for feedback. Dr Murray goes on to say "Unfortunately many mistakes can occur with this method. If an abnormality is not recognized by the untrained person performing the exam, or the images are of poor quality, the radiologist cannot make an accurate assessment of the animal. This technique should be a last resort, for geographic areas where there is no radiologist or internist available."


Ultrasonography of the feline kidney: technique, anatomy and changes associated with disease (2012) Debruyn K, Haers H, Combes A, Paepe D, Peremans K, Vanderperren K & Saunders JH Journal of Feline Medicine and Surgery 14(11) pp794-803 has detailed information about kidney ultrasounds in cats.


Renal ultrasound Blok BK & Hoffmann B Ultrasound Guide for Emergency Physicians: An Introduction is about humans and is quite technical, but it has some kidney images you may find helpful.


Ultrasound: Findings

The kidneys of a typical healthy cat will be between 3 and 4.3 cm (around 1.25 to 1.75 inches) in length, though in some cats they may be a little longer. The size of the cat is a factor, with females tending to have smaller kidneys than males.


Healthy kidneys are oval or shaped like a bean, and smooth.


CKD cats tend to have small, shrivelled kidneys with an irregular shape.


Diagnostic imaging: ultrasound of cats with chronic kidney failure not always black and white (2008) Zwingenberger A DVM News Magazine explains how CKD kidneys look different to healthy ones.


Ultrasound of cats with chronic renal disease (2007) Zwingenberger A Veterinary Radiology explains more about what normal kidneys look like on ultrasound, and what differences you may see in CKD and end stage CKD kidneys.


In cases of kidney infection (pyelonephritis), the renal pelvis may be dilated (this is known as pyelectasis), which should be visible on ultrasound (though this may not occur in the case of acute infections). This dilation may also occur when kidney stones or other obstructions are present. Feline chronic renal disease - acute presentation (2007) Zwingenberger A Veterinary Radiology explains more about how acute kidney injury looks on ultrasound, including information on cases of obstruction or pyelonephritis.


Renal ultrasonography: kidneys big, small and in-between (2011) Armbrust LJ CVC in Kansas City Proceedings discusses the changes that may be seen in cases of enlarged kidneys.




X-rays can be used to look at the kidneys and to check for kidney stones, but in most cases palpation and, if necessary, the use of ultrasound make the use of x-rays unnecessary. 


X-rays may require the cat to be sedated. Some members of Tanya's CKD Support Group have been allowed to don lead aprons and hold their cats still for the x-ray instead, but not every vet permits this.


Long Beach Animal Hospital has information on x-rays.


Renal imaging in cats (2008) Seyrek-Intas D & Kramer M Veterinary Focus 18(2) pp23-30 discusses x-rays.


Intravenous Pyelogram (IVP)


An IVP is a special type of X-ray which uses a contrast agent to clearly show the urinary tract. IVPs may be used when tumours or blockages are suspected. However, the dyes used as a contrast agent may be toxic to the kidneys, particularly if there is a blockage. The dyes are also excreted by the kidneys, which is a risk for cats with advanced CKD. These risks must be borne in mind when deciding whether to have this procedure.


Children's Hospital of Wisconsin has information on this procedure in humans.


Planar Renal Scintigraphy


This is a helpful way of evaluating kidney function and does not require anaesthesia in most cases. However, it is only available at a small number of centres, so is normally only used to assess kidney function prior to removing a kidney because of a tumour or prior to a nephrectomy (cutting into the kidney, e.g. to remove kidney stones). It is unlikely to be of any benefit for the typical CKD cat with small, scared kidneys.


Advanced Medical Veterinary Imaging (2014) has a helpful overview of renal scintigraphy.


Renal imaging in cats (2008) Seyrek-Intas D & Kramer M Veterinary Focus 18(2) pp23-30 discusses planar renal scintigraphy.




This may be used in cases where cancer is suspected. Since it requires an anaesthetic, it should only be done where absolutely necessary.  


For general CKD cases, it is unlikely that a biopsy will be of sufficient value to justify the risks associated with it. Choosing the right biopsy for the job (2006) Wilcock B HistoVet states "With careful assessment of serum biochemistry and urinalysis, biopsy is rarely indicated and (except for glomerular disease) almost impossible to interpret." Discuss this in more detail with your vet in case there may be a valid reason in your cat's case.


If your cat does require a biopsy, read the guidelines on anaesthesia for CKD cats.


Renal biopsies: what are some benefits and risks (2002) Osborne C DVM360 Magazine discusses biopsies.


Renal disease/urology (2003) Ross SR has a section entitled A special note on renal biopsies! (scroll down a little to find it).


Renomegaly (Enlarged Kidneys)


Most CKD cats have small, scarred kidneys, but some kidney-related conditions may cause the opposite problem of enlarged kidneys. These conditions are discussed in more detail elsewhere on the site:

Ultrasonography best to assess character, consistency of renal parenchyma (2002) Hoskins JD DVM360 Magazine discusses renomegaly.


Pet MD has an overview of renomegaly.


Renal ultrasonography: kidneys big, small and in-between (2011) Armbrust LJ CVC in Kansas City Proceedings discusses the changes that may be seen on ultrasound in cases of enlarged kidneys.



Hydronephrosis may cause enlargement of the kidneys with urine because of obstruction of the ureter, which prevents urine from passing through. Cats with acute kidney injury may have enlarged kidneys, often (but not always) because of such an obstruction.


Pet Place has information on hydronephrosis.


National Kidney Foundation has some information about hydronephrosis in humans.


Big Kidney Little Kidney

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


In Acute uremia in cats (2008) Ross S Veterinary Focus 18(2) Dr Ross says "Sustained obstruction leads to fibrosis and atrophy of the corresponding kidney and compensatory hypertrophy of the contralateral kidney. The disease remains clinically silent until obstruction of the contralateral ureter occurs. This process explains the classic "big kidney-little kidney" scenario typical of many cats diagnosed with acute ureteral obstruction."


Cats with chronic renal failure (CRF) - how different than CRF in dogs? (2007) is a presentation by DJ Chew and SP DiBartola to the World Small Animal Veterinary World Congress which mentions big kidney little kidney syndrome.







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This page last updated: 26 February 2018

Links on this page last checked: 30 April 2017








I have tried very hard to ensure that the information provided in this website is accurate, but I am NOT a vet, just an ordinary person who has lived through CKD with three cats. This website is for educational purposes only, and is not intended to be used to diagnose or treat any cat. Before trying any of the treatments described herein, you MUST consult a qualified veterinarian and obtain professional advice on the correct regimen for your cat and his or her particular requirements; and you should only use any treatments described here with the full knowledge and approval of your vet. No responsibility can be accepted.


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