Benefits of Early Detection

Types of Test Available

SDMA Blood Test

Urine Tests, Including Urine Specific Gravity (USG) and Proteinuria

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FGF-23 Test



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Home > What is CKD? > Early Detection



  • As discussed on the What Happens in CKD? page, it is normally not possible to detect CKD until the cat has already lost 66-75% of his or her kidney function, although the new SDMA test may change this.

  • This page discusses some areas of investigation into ways in which earlier detection may be possible.

  • It is not currently possible to prevent CKD; but the earlier it is diagnosed, the better your chances of helping your cat.

Benefits of Early Detection

It may appear that there is no real benefit in early detection, because it is not possible to cure CKD, and knowing at an early stage that your cat has it may distress you. However, there are in fact some benefits to knowing early:

  • You can try to find a cause and treat accordingly.

  • You can avoid using potentially nephrotoxic treatments such as certain painkillers.

  • You can make early changes that may be beneficial such as dietary changes.

  • You can take appropriate precautions when treatments such as dental surgery are undertaken.

  • You can watch for urinary tract infections, which may further damage the kidneys.

  • You can monitor your cat for problems associated with CKD, such as high blood pressure or anaemia, before these become severe and potentially life threatening.

  • You can avoid your cat only being diagnosed following a sudden crash, with the attendant risks and guilt.

Types of Test Available


The gold standard for measuring kidney function in cats is via glomerular filtration rate (GFR). Unfortunately this is not easily measured in cats, so in practice the usual way to diagnose CKD has been via elevated creatinine (and to a much lesser extent, BUN or urea) levels in the blood, and via certain urine tests. However, creatinine does not tend to rise in CKD cats until 60-70% of kidney function has already been lost, which means that a cat can actually be in Stage 1 or 2 of CKD according to the IRIS staging system (see How Bad is It?) but still have a creatinine that falls within supposedly normal limits.


Because of this, there have been many attempts to find a way of diagnosing CKD earlier in cats. These tests are described below, but many of them are not mainstream and are therefore either not widely available or are difficult to use. The most useful one is probably going to be the new (2015) SDMA blood test.


The International Renal Society (2013) has an article about early detection.

Assessment of renal function: what can be done in practice (2002) Elliott J Presentation to the World Small Animal Veterinary Association Congress discusses the various methods of detecting CKD.


The tests fall into the following categories:


Widely Available

Not Widely Available

Blood Tests


SDMA (Symmetric Dimethylarginine) Test


What is SDMA?

SDMA is a methylated form of arginine, an amino acid. It is released when protein is processed, and is eliminated largely (over 90%) by the kidneys. Because of this, it was thought that increased levels of SDMA might correlate with the development of CKD. One human study, Symmetrical dimethylarginine: a new combined parameter for renal function and extent of coronary artery disease (2006) Bode-Böger SM, Scalera F, Kielstein JT, Martens-Lobenhoffer J, Breithardt G, Fobker M & Reinecke H Journal of the American Society of Nephrology 17 pp1228-1134 concluded that "SDMA might be a useful parameter for detecting patients in very early stages of chronic kidney disease and for determining their risk for developing cardiovascular disease."


The SDMA Test

The SDMA Test for cats was developed by Ohio State University College of Veterinary Medicine and IDEXX Laboratories, and became available commercially in 2015. Comparison of serum concentrations of symmetric dimethylarginine and creatinine as kidney function biomarkers in cats with chronic kidney disease (2014) Hall JA, Yerramilli M, Obare E, Yerramilli M & Jewell DE Journal of Veterinary Internal Medicine 28 pp1676–1683 found that SDMA levels in cats who developed CKD rose above normal by a mean of 17 months before there was an increase in creatinine levels.


IDEXX claim that the SDMA test can therefore potentially detect CKD when up to 40% of function has been lost, whereas traditionally you could only detect CKD when 60-70% of function had been lost.


IIDEXX provides an introduction to the SDMA test.


How to Run the Test

The beauty of the SDMA test is that it can simply be run as part of a standard blood chemistry blood test from IDEXX. In fact, if you are in the USA and your vet uses IDEXX for blood chemistry panels, the SDMA test will be provided at no additional charge during summer 2015. If your vet uses in-house testing for most tests but has a relationship with IDEXX, the test can be ordered separately from the IDEXX laboratory. I have already seen a number of test results which include SDMA, but that's not too surprising: Reuters reports that more than 100,000 patients were tested in the two weeks following the test's launch in July 2015.


The test will become available in Canada in the summer of 2015, and in Europe and other international markets in January 2016.


If your vet uses another laboratory such as Antech, you can still request the test, but Antech will have to send it to IDEXX so there will be a charge.


Interpreting the Results

IDEXX have provided the following guidelines for the test.


Measurement IDEXX Staging

0-14 ug/dl

Normal kidney function

15-20 ug/dl

Early kidney disease
Over 20 ug/dl More advanced kidney disease


IDEXX recommend that the test should not be run in isolation but in conjunction with creatinine and urinalysis. Your vet should also rule out pre-renal causes and causes of acute kidney injury.


IDEXX notes that for cats with SDMA and/or creatinine at the upper end of the normal range, CKD cannot be ruled out, and recommends urinalysis.


The International Renal Interest Society has apparently agreed to incorporate SDMA results into its staging guidelines. These are the proposed changes for cats with persistently elevated readings, according to a Press Release:


Measurement Current IRIS Staging IRIS Staging

Over 14 ug/dl

Stage 1 Stage 1

Over 20 ug/dl

Stage 2 but with a low body condition score Treat as if in Stage 3
Over 45 ug/dl Stage 3 but with a low body condition score Treat as if in Stage 4


Only 1% of cats will have a reading over 50 ug/dl.


IDEXX explains what to do next if your cat has a positive SDMA test. You can also read more about how to manage your cat's current condition on the How Bad is It? page.


SDMA FAQS answers frequently asked questions about the SDMA test.


Urine Tests


Urine Specific Gravity                                                                                          


Measuring urine specific gravity may indicate loss of concentrating ability before anything shows in bloodwork. However, a cat may have dilute urine for other reasons, such as diabetes, so this is only a guide, not a definitive method of diagnosis. Also, once a cat is receiving fluid therapy, USG can be rather unreliable.


The International Renal Interest Society has information on the significance of USG in cats.



The International Renal Interest Society (2013) views protein in the urine, which is known as proteinuria, as a risk factor for the development of CKD, and as a factor to determine the severity of the CKD.


Evaluation of predictors of the development of azotaemia in cats (2009) Jepson RE, Brodbelt D, Vallance C, Syme HM, Elliott J. Journal of Veterinary Internal Medicine 23(4) pp806-13 reports on a group of older cats who were monitored to see if they developed CKD. The study concludes that "Proteinuria at presentation was significantly associated with development of azotemia although causal association cannot be inferred."


Protein in the urine may have causes other than CKD. There is more information about proteinuria on the Urinalysis page.


If you know your cat has proteinuria early on, you can take steps to control it, see Treatments.


The following tests may be helpful in assessing the presence of proteinuria:

Urine:PC Ratio

Idexx Laboratories offers a test in a number of different countries which can calculate the protein:creatinine ratio. It is part of their catalyst 1 test.


E.R.D.-HealthScreen Urine Test                                                                                           

The E.R.D.-HealthScreen Urine Test is another test which may assist with detecting CKD in its early stages by detecting low levels of protein (microalbuminuria) in the cat's urine. The manufacturer claims that the test is able to detect cats at risk of CKD when there is as little as 25% kidney damage, compared to the 60-70% loss of function that occurs before anything shows up in creatinine levels.


The test is only available through your vet, who has to run the test in-house. If your vet does not have any in stock and you are in Europe, s/he can contact Heska's European distributors to obtain the test. Heska also has a list on its website of its distributors in other parts of the world.


In the USA it should not cost more than US$20-30 if performed in addition to other tests (Antech charges much less); it may cost slightly more if run in isolation. Unfortunately, it appears to be much more expensive in Europe, costing up to €200, though many vets will charge less.


The test is non-invasive, requiring only a urine sample, with results available in-house in less than five minutes. If the test is positive, further investigations should be performed, e.g. for high blood pressure. The test may also be positive if certain inflammatory diseases such as IBD or dental disease are also present, or if the cat has certain other conditions such as diabetes or hyperthyroidism.


Drugs has some information about the test.


Glomerular Filtration Rate                                                                                      


The International Renal Interest Society (2013) states that the glomerular filtration rate (see What Happens in CKD) is "considered the single most useful and sensitive test of renal function." IRIS believes that eventually GFR will be the measure by which CKD can be categorised, although it will take some time to determine appropriate reference ranges.


The main problem with measuring GFR is that it is quite cumbersome, requiring the injection of contrast agents followed by precisely timed blood tests. Therefore few vets are able or willing to do it.


Managing chronic kidney disease: 10 common questions (2012) Brown SA Presentation to the 83rd FVMA Annual Conference discusses more about GFR and the various ways of measuring it.


Relationship between serum symmetric dimethylarginine concentration and glomerular filtration rate in cats (2014) Braff J, Obare E, Yerramilli M, Elliott J & Yerramilli M Journal of Veterinary Internal Medicine 28 pp1699–1701, a study conducted by IDEXX, found a correlation between increased levels of SDMA in cats and a low GFR. It may therefore be helpful to consider the simple new SDMA bloodtest available from IDEXX.


The following tests can be used to directly assess GFR:

Iohexol Clearance Test (Plasma Iohexol Clearance Test)

This test uses iohexol, an iodinated radiographic contrast medium. Basically, the test measures how long it takes to clear a measured amount of iohexol from the kidneys, and this is then used to calculate the GFR. This test, sometimes referred to as the Plasma Iohexol Clearance test (PIC) is highly specialised and only available at a limited number of places in USA such as the Animal Health Diagnostic Laboratory at Michigan State University; I am not aware that the test is commercially available in Europe. This test may be particularly helpful  before opting for one of the more permanent methods of treating hyperthyroidism.


Estimation of glomerular filtration rate via 2- and 4-sample plasma clearance of iohexol and creatinine in clinically normal cats (2009) Heiene R, Reynolds BS, Bexfield NH, Larsen S & Gerritsen RJ American Journal of Veterinary Research 70(2) pp176-85 is a study into determining appropriate reference ranges. It found that the weight of the cat is a factor.

Michigan State University Diagnostic Center for Population and Animal Health has some information on GFR and can run the iohexol clearance test.

Current concepts for the management of chronic renal failure in the dog and cat - early diagnosis and supportive care (2005) is a presentation by Dr S Sanderson to the World Small Animal Veterinary Association World Congress which mentions this test.


Inulin Clearance Test

Like the iohexol clearance test, the inulin clearance test measures how long it takes the kidneys to clear a measured amount of a particular substance, in this case inulin. This test only requires a single IV injection of inulin, followed by the taking of a blood sample three hours later. The test is already commercially available in Germany. This test may be particularly helpful  before opting for one of the more permanent methods of treating hyperthyroidism.


Single-injection inulin clearance for routine measurement of glomerular filtration rate in cats (2003) Haller M, Rohner K, Muller W, Reutter F, Binder H, Estelberger W, Arnold P Journal of Feline Medicine & Surgery 5 (3) pp175-81 compared the inulin test to the iohexol clearance test and concluded that "the inulin clearance test is a valuable tool for the assessment of renal function in daily practice".

Alomed in Germany is offering this test.


Fibroblast Growth Factor 23 (FGF-23)


Fibroblast growth factor 23 (FGF23) is important for the regulation of phosphorus levels in the body. Since phosphorus and parathyroid hormone (PTH) imbalances are common in CKD, it is possible that FGF-23 levels may in fact rise before other signs of CKD appear. In humans, such increases have been identified before any changes in PTH and phosphorus levels.


Fibroblast growth factor 23 (FGF-23) concentrations in cats with early non-azotemic chenic kidney disease (2013) Finch NC, Geddes RF, Syme HM & Elliott J Journal of Veterinary Internal Medicine 27 pp227-233 measured levels of FGF-23 in geriatric cats. The study found that FGF-23 levels were significantly higher in cats who were apparently healthy at the start of the study but who subsequently went on to develop azotaemia. It also indicated an association between FGF-23 and secondary hyperparathyroidism. The authors indicate that this test may be helpful for indicating problems with phosphorus balance in CKD cats, but state that further studies are warranted.


As far as I know, this test is not routinely available to vets.





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This page last updated: 08 August 2015

Links on this page last checked: 08 August 2015