Chronic kidney disease (CKD) is persistent damage or dysfunction in a cat’s kidneys. A single high blood result or a symptom such as weight loss does not prove CKD: veterinarians combine the cat’s history and examination with blood tests, urinalysis and, when appropriate, repeat testing or other investigations. They assign an IRIS stage only after CKD has been diagnosed.
What does chronic kidney disease mean for my cat?
The kidneys filter waste from the blood and help regulate fluid balance, electrolytes and other body processes. CKD means kidney disease that persists over time; it is not simply one abnormal test result. Early CKD may cause no obvious signs. As it progresses, a cat may lose weight, eat less, seem lethargic or develop an unkempt coat, but none of these signs alone confirms kidney disease.
CKD is common in older cats, although estimates vary by population. Cornell University College of Veterinary Medicine reports that it affects up to 40% of cats over age 10 and 80% of cats over age 15. These are estimates, not rates that apply identically to every group of cats. Cornell Feline Health Center: Chronic Kidney Disease
How do vets diagnose kidney disease in cats?
Veterinarians look for a consistent pattern across the cat’s clinical history, physical examination and laboratory results. Blood tests and urinalysis provide complementary information: blood tests assess waste markers and other effects of kidney dysfunction, while urine tests help show how well the kidneys concentrate urine and whether protein, blood cells or other abnormalities are present.
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History and examination
The veterinarian considers changes such as appetite, weight, activity and drinking or urination, along with examination findings and the cat’s overall stability. These clues guide testing, but signs are not specific enough to establish CKD on their own.
Blood tests
Common kidney-related blood measurements include blood urea nitrogen (BUN), creatinine and symmetric dimethylarginine (SDMA). The veterinarian may also consider electrolytes, phosphorus, red blood cell counts and protein concentrations. These results help build the picture but can be influenced by factors beyond kidney disease.
Urinalysis and related urine tests
Urinalysis can assess urine concentration, measured as urine specific gravity, as well as pH, protein, blood cells, bacteria and other cells. A urine protein-to-creatinine ratio (UPC) helps evaluate protein loss in urine. A urine culture may be used to check for bacterial infection. Which tests are appropriate depends on the cat and the findings so far.
Blood pressure and imaging
Blood pressure matters because high blood pressure can accompany CKD and affect a cat’s health. Cornell reports that approximately 60% of cats with CKD develop hypertension. Ultrasound or radiographs may help in selected cases, and biopsy is used in some circumstances; these are not required for every suspected case.
What do creatinine and SDMA mean?
Creatinine and SDMA are blood markers used to assess kidney function, but neither diagnoses CKD by itself. Their results are interpreted alongside one another, the urine findings and the cat’s condition.
| Marker | What can affect or limit it | Approximate timing noted by Cornell |
|---|---|---|
| Creatinine | Dehydration can increase it; low muscle mass can make it deceptively normal despite reduced kidney function. | Cornell reports that it generally does not rise until almost 75% of renal function is lost. This is an approximate source figure, not a rule for an individual cat. |
| SDMA | Less affected than creatinine by hydration and muscle mass, but still must be interpreted with other clinical evidence. | Cornell reports that it may rise when about 40% of renal function is lost. This is an approximate source figure, not an individual-cat threshold. |
These approximate thresholds explain why the markers can differ; they do not predict exactly when a particular cat’s result will change. Cornell’s discussion of the markers and their limitations is available in its CKD overview.
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Does one high kidney value mean my cat has CKD?
No. A single abnormal result may be a reason to investigate, but it does not establish persistent kidney disease. Dehydration can raise BUN and creatinine even when kidney function is normal. Conversely, a cat with low muscle mass may have a creatinine result that looks reassuring despite reduced function. Recent fluid treatment can also lower measured urine concentration.
When results are unclear or do not agree, repeat testing in a stable, adequately hydrated cat can help determine whether abnormalities persist. Cornell says kidney function is ideally interpreted using at least two blood and urine samples collected within two weeks from a stable, well-hydrated cat. IRIS advises considering all available clinical and laboratory evidence and persistence over time; when results are discrepant, it describes repeating testing at about two weeks, with later follow-up adjusted to the patient’s circumstances. These are clinical guidance points, not a schedule to apply without the veterinarian.
Why does my cat need a urine test and blood pressure check?
Blood and urine tests answer different questions. Blood markers show changes in substances that the kidneys help clear, while urinalysis can reveal whether urine is concentrated and whether protein, blood cells or bacteria are present. UPC can quantify urinary protein loss, and culture can help identify infection. Blood pressure is checked because hypertension is an important associated problem and can influence care. Together, these findings help the veterinarian distinguish a persistent kidney pattern from a temporary or misleading abnormality.
How urine samples may be collected
The clinic should advise how to collect a sample, because the best method depends on the test needed and the cat. A non-absorbent litter collection kit is one possible way to obtain urine at home, but it is not necessary for every cat or every test. A home collection product does not replace veterinary urinalysis, culture or interpretation.
When does IRIS staging happen?
The International Renal Interest Society (IRIS) stages confirmed CKD; staging is not a way to establish the diagnosis in the first place. The system uses kidney-function markers, including creatinine and SDMA, and recommends substaging based on urine protein and systemic arterial blood pressure. Staging should be done when the cat is stable and well hydrated, since dehydration or acute illness can make results look worse. It helps veterinarians communicate and guide management, but does not by itself predict an individual cat’s course.
IRIS’s guideline index notes that its board reissued core guidance as 2026 revisions. Those revisions include treatment-document updates, including clearer hematocrit thresholds; they are not evidence of a new diagnostic test. See the IRIS Staging System and IRIS Guidelines.
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