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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 not normally possible to detect CKD until the cat has already lost 66-75% of his or her kidney function, although the SDMA test may offer earlier indications of a problem.

  • 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 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.

CKD early diagnosis (2019) Syme H International Renal Interest Society explains more about early detection and suggests obtaining baseline bloodwork when your cat is healthy, so you can monitor trends for your cat.


Types of Test Available


Glomerular filtration rate (see below) is the gold standard for assessing kidney function in cats. Unfortunately GFR is not easy to measure in cats, so although I do discuss it below, you are unlikely to be offered this test unless you attend a vet school.


Historically, the usual way to diagnose CKD in cats 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. In addition, since creatinine is a by-product of muscle and is higher when a lot of muscle is present, a large muscular cat may be suspected of having CKD when he does not, whereas a CKD cat who has lost a lot of weight and muscle might not be diagnosed promptly.


Because of this, there have been many attempts to find a way of diagnosing CKD earlier in cats. The SDMA test was introduced in 2015 and is now routinely offered.


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.


See Other Diagnostic Tests to read about an initial study into the possible use of ultrasound to diagnose CKD in cats.


Biomarkers of kidney disease: potential utilities (2018) Segev G International Renal Interest Society discusses the benefits of early detection and mentions some possible tests, though none of these is widely available as yet apart from the SDMA test.


The tests fall into the following categories:


Widely Available Tests

Not Widely Available Tests

Blood Tests


Most vets will check your cat's creatinine and BUN (or urea) levels. You may also be offered the SDMA test.


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, increased levels of SDMA may 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."


As mentioned above, creatinine may appear lower than it truly is if the cat has lost muscle mass. One advantage of the SDMA test is that, as Early diagnosis of chronic kidney disease in dogs and cats: use of serum creatinine and symmetric dimethylarginine (2016) Grauer GF Today's Veterinary Practice Mar/Apr 2016 states, "In contrast to sCr, SDMA should not be affected by changes in muscle mass."


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 states 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.


More than 100,000 patients were tested in the two weeks following the test's launch in July 2015. The test became available in Canada in the summer of 2015, and in Europe and other international markets in January 2016.


SDMA: How to Run the Test

The SDMA test can simply be run as part of a standard blood chemistry blood test from IDEXX. If you are in the USA and your vet uses IDEXX for blood chemistry panels, the SDMA test should be provided routinely. 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.


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.


SDMA: Interpreting the Results

IDEXX have provided the following guidelines for the test:



IDEXX Staging

0-14 ug/dl

Normal kidney function

15-20 ug/dl

Early kidney disease

Over 20 ug/dl

More advanced kidney disease


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


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 (such as dehydration) and causes of acute kidney injury (AKI) because SDMA may be elevated in cases of AKI or if any other condition is present that reduces blood flow through the kidneys.


Symmetric dimethylarginine in cats with hypertrophic cardiomyopathy and diabetes (20180 Langhorn R, Kieler IN, Koch J, Christiansen LB & Jessen LR Journal of Veterinary Internal Medicine 32(1) pp57-63 looked at SDMA levels in cats with HCM or diabetes. It concludes "Serum SDMA concentrations in cats with HCM were not significantly different from those of healthy control cats. Cats with DM, however, had significantly lower SDMA concentrations than controls, a finding that needs further investigation and should be kept in mind when evaluating renal function of cats with this endocrinopathy." I take this to mean that a cat with both CKD and diabetes might have lower SDMA levels than if the cat had CKD only.


Creatinine levels are naturally higher in Birman cats, which may lead some Birmans to receive an incorrect diagnosis of CKD. Serum symmetric dimethylargininr and creatinine in Birman cats compared with cats of other breeds (2018) Paltrinieri S, Giraldi M, Prolo A, Scarpa P, Piseddu E, Beccati M, Graziani B & Bo S Journal of Feline Medicine and Surgery 20(10) pp905-912 found that levels of SDMA are also higher in Birman cats, though not as much as creatinine. The study states that Birman cats should be assessed based on SDMA as well as creatinine, and using a specialised reference range for Birmans.


Symmetric dimethylarginine in hyperthyroid cats before and after treatment with radioactive iodine (2020) DeMonaco SM, Panciera DL, Morre WA, Conway T & Werre S Journal of Feline Medicine and Surgery 22(6) pp531-538 found that SDMA increases in cats treated with I131 for hyperthyroidism, and states that SDMA should be considered alongside creatinine and USG in hyperthyroid cats before treatment.


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.


Some people believe the SDMA test may not be accurate for kittens, but IDEXX have established a kitten reference interval.


IRIS staging of CKD (2019) International Renal Interest Society refers to SDMA results in its staging guidelines. For cats with persistently elevated SDMA readings, it suggests changes in the stage of CKD the cat is deemed to be in as follows:


Current IRIS Staging Based on Other Criteria

SDMA Measurement

Revised IRIS Staging

Stage 1

Over 18 ug/dl

Stage 1

Stage 2 but with a low body condition score

Over 25 ug/dl

Treat as if in Stage 3

Stage 3 but with a low body condition score

Over 38 ug/dl

Treat as if in Stage 4


SDMA: What To Do Next

IDEXX SDMA algorithm 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.


SDMA may be useful for helping confirm the CKD diagnosis, but once your cat has had a positive test, repeating the test is unlikely to be of value in most cases, though Early diagnosis of chronic kidney disease in dogs and cats: use of serum creatinine and symmetric dimethylarginine (2016) Grauer GF Today's Veterinary Practice Mar/Apr 2016 says that "cats with borderline sCr and/or SDMA concentrations should be retested: Two weeks after initial testing to confirm the initial value, Then approximately every 3 months to assess renal function stability."


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.


Urine specific gravity (2015) Watson ADH,  Lefebvre HP & Elliott J International Renal Interest Society has information on the significance of USG in cats.



Proteinuria (2016) Grauer GF International Renal Interest Society explains how protein in the urine, which is known as proteinuria, is a risk factor for the development of CKD, and also a factor in determining 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 Proteinuria page.


Urine:PC Ratio

Proteinuria is assessed via the urine:PC ratio test.


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.


A similar test is also available from Antech.




RenalTech is an artificial intelligence (AI) predictive tool developed by Antech, which claims it can detect CKD up to two years earlier than other methods, and with 95% accuracy in some cases. The system assessed the records of more than 100,000 cats who visited a chain of veterinary clinics three or more times between 1995 and 2017. Predicting early risk of chronic kidney disease in cats using routine clinical laboratory tests and machine learning (2019) Bradley R, Tagkopoulos I, Kim M, Kokkinos Y, Panagiotakos T, Kennedy J, De Meyer G, Watson P & Elliott J Journal of Veterinary Internal Medicine 33(6) pp2644-2656 explains more about how the tool was developed.


The test results needed to use the tool are ones you would usually be monitoring anyway:

Cats are placed in one of three categories based on their results:

  • Negative: highly unlikely to develop CKD in the next two years. Run the tests again in a year.

  • Inconclusive: insufficient certainty to predict the likelihood of CKD. Run the tests again in 3-6 months.

  • Positive: highly likely to develop CKD in the next two years. Use IRIS staging guidelines.

The tool is available to vets in the USA who use Antech's reference laboratory services.


Antech provides a RenalTech Care Pathway.


Glomerular Filtration Rate


Glomerular filtratrion rate in dogs and cats (2013) Heiene R & Lefebvre HP International Renal Interest Society states that the glomerular filtration rate (see What Happens in CKD) is "considered the single most useful and sensitive test of renal function." It is also the best way to detect CKD early because GFR reduces before a rise in creatinine is apparent. It goes on to say "Assessment of GFR is therefore pivotal for evaluating severity and progression of renal diseases, especially chronic kidney diseases (CKD)."


Unfortunately measuring GFR 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. Early diagnosis of chronic kidney disease in dogs and cats: use of serum creatinine and symmetric dimethylarginine (2016) Grauer GF Today's Veterinary Practice Mar/Apr 2016 states "due to expense, time, and labor, GFR is rarely measured in the practice setting." GFR measurement is available at most vet schools and I understand the Royal Veterinary College can do it for around £180 (2016 price).


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. If you are unable to have GFR tested, you might wish to consider the SDMA test instead, though this is not as accurate as GFR testing.


Clinical evaluation of glomerular filtration rate (2015) DiBartola SP Presentation to Idexx Finland Congress discusses the various ways of measuring GFR.


Managing chronic kidney disease: 10 common questions (2012) Brown SA Presentation to the 83rd FVMA Annual Conference discusses GFR and how to measure it.


An overview of glomerular filtration testing in dogs and cats (2011) Von Hendy-Willson VE & Pressler BM Veterinary Journal 188(2) pp156–165 has a detailed, albeit technical, overview.


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. Some people use this test before opting for one of the more permanent methods of treating hyperthyroidism.


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.


Michigan State University Veterinary Diagnostic Laboratory can run the test for you for US$111 using this form. Search for test code 70029 if necessary. Ensure your vet follows the Collection protocol.


Practical matters: practical ways to measure GFR in your patients (2011) Langston CE Veterinary Medicine explains more about how the test is performed and says "Although iodine allergic reaction or development of mild reversible acute kidney failure has been reported in people undergoing this type of test, the risk in animals appears to be low."


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.


Current concepts for the management of chronic renal failure in the dog and cat - early diagnosis and supportive care (2005) Sanderson S Presentation 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 requires a single IV injection of inulin, followed by taking a blood sample three hours later. The test is commercially available in Germany.


Some people use this test 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 offers this test.


Fibroblast Growth Factor 23 (FGF-23)


Fibroblast growth factor 23 (FGF-23) 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 chronic 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.


Relationship betweem plasma fibroblast growth factor-23 concentration and survival times in cats with chronic kidney disease (2015) Geddes RF, Elliot J & Syme HM Journal of Veterinary Internal Medicine 29(6) pp1494-1501 states "Plasma FGF-23 is noted to increase early in the development of CKD, before obvious evidence of hyperphosphatemia. It is not known if FGF-23 is a uremic toxin or more a surrogate marker for other causes of uremic toxicity."


This study also found a correlation between FGF-23 levels and survival time, with cats with an FGF-23 level below 700 pg/mL having a median survival time of 577 days, compared to cats with an FGF-23 level of 3000-10000 pg/mL surviving a median of 277 days. Cats with a level over 10000 pg/mL had a median survival time of only 38 days.


This test is not currently available to vets.


Recent advances in mineral and bone disorders in CKD Van den Broek H & Elliott J International Renal Interest Society has some information about FGF-23.


Renal Biomarkers


Renal biomarkers (2018) Segev G International Renal Interest Society discusses the use of various biomarkers that might assist with the early detection of CKD.




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This page last updated: 27 June 2020

Links on this page last checked: 25 June 2020







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.


If your cat appears to be in pain or distress, do not waste time on the internet, contact your vet immediately.



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