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DISEASE · CATS

Kidney disease in cats: IRIS stages, blood work and monitoring

Chronic kidney disease (CKD) is one of the most common diseases of older cats. It usually progresses slowly, and blood and urine tests can detect it before obvious signs appear. Here is how vets diagnose it, stage it and follow it over time.

Written by the AI DiagAnimals editorial teamReviewed by the AI DiagAnimals TeamUpdated Our editorial policy

The essentials

Chronic kidney disease may affect 30–40% of cats over 10 years of age. It is diagnosed on a persistently high creatinine or SDMA together with a dilute urine (specific gravity below 1.035). IRIS stages it from 1 to 4 on fasting creatinine and SDMA, then substages it by urine protein (UPC) and blood pressure. Anaemia, low potassium, high phosphorus and high blood pressure are common and each is monitored.

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What chronic kidney disease is

CKD is a lasting loss of kidney function, usually progressive. It may affect 30–40% of cats over 10 years of age, and age is the only clear risk factor; the cause is often unknown [1].

The ISFM guidelines advise health checks every 6 months for cats over 7 years, with blood tests and a urinalysis at least once a year, so that changes are caught early [1].

Early signs of kidney disease in cats

  • Drinking and urinating more.
  • Weight loss and a poorer coat.
  • Reduced appetite, nausea or vomiting as the disease advances.
  • Weakness or constipation, sometimes linked to a low potassium [1].
  • Sudden blindness, from high blood pressure [2].

How it is diagnosed

In practice, CKD is diagnosed on a creatinine above 1.6 mg/dL (140 µmol/L) with an inappropriately dilute urine (specific gravity below 1.035), sustained over several weeks or months [1]. A persistently high SDMA can reveal early CKD (stage 1) before creatinine rises [3].

Some cats with CKD still concentrate their urine, and kidney damage can exist without a high creatinine, which is why the urine and the trend are always read together [1].

The IRIS stages in cats

IRIS 2026, based on fasting creatinine and/or SDMA measured at least twice in a hydrated, stable cat with CKD. If SDMA is persistently higher than the creatinine stage suggests, the cat is staged one stage higher [3].
StageCreatinine (mg/dL)Creatinine (µmol/L)SDMA (µg/dL)
1below 1.6below 140below 18
21.6–2.8140–25018–25
32.9–5.0251–44026–38
4above 5.0above 440above 38

Substages: urine protein and blood pressure

IRIS substages, aligned with the ACVIM hypertension consensus [2, 3]. Proteinuria is confirmed on at least two samples over at least two weeks [3].
MeasurementCategory
UPC below 0.2Non-proteinuric
UPC 0.2–0.4Borderline proteinuric
UPC above 0.4Proteinuric
Systolic pressure below 140 mmHgNormotensive (minimal risk)
140–159 mmHgPrehypertensive (low risk)
160–179 mmHgHypertensive (moderate risk)
180 mmHg or moreSeverely hypertensive (high risk)

Proteinuria matters: in one study, cats with a UPC below 0.2 lived a median of about 1,000 days, versus about 400 days above 0.4 [1]. High blood pressure is found in 19–40% of cats with CKD in general practice [1].

The other values vets follow

  • Anaemia: seen in 30–65% of cats with CKD, from a lack of the kidney hormone erythropoietin [1]. See anemia in cats.
  • Potassium: often low, from losses in the urine; it can cause weakness [1]. See potassium in dogs and cats.
  • Phosphorus: a high value is associated with faster progression; a phosphate-restricted diet is thought to explain much of the longer survival on kidney diets [1].
  • Urine culture: urinary infections occur in about 15–30% of cats with CKD and more than 70% cause no signs [1].

What to expect

The outlook depends mainly on the stage at diagnosis. In a study of 211 cats with a creatinine above 2.3 mg/dL, median survival was 1,151 days for cats diagnosed in late stage 2, 778 days in stage 3 and 103 days in stage 4 [4]. Many cats live well for years with treatment adjusted to their stage.

Related articles

En français : l’insuffisance rénale du chat.

Questions to ask your veterinarian

  1. Which IRIS stage and substages does my cat have?
  2. What do the urine specific gravity and UPC show?
  3. What is my cat’s blood pressure, and how often should it be checked?
  4. Are potassium, phosphorus and the red cells within target?
  5. How often should we repeat the blood and urine tests?
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Frequently asked questions

What are the early signs of kidney disease in cats?

Drinking and urinating more, weight loss and a poorer coat. Blood and urine tests can detect it before these signs appear [1].

How long will a cat live with kidney disease?

It depends on the stage at diagnosis and on proteinuria. In one study, median survival was 1,151 days in late stage 2, 778 days in stage 3 and 103 days in stage 4 [4].

What are the IRIS stages in cats?

Four stages based on fasting creatinine and SDMA, from stage 1 (creatinine below 1.6 mg/dL) to stage 4 (above 5.0 mg/dL), substaged by urine protein and blood pressure [3].

What should a cat with kidney disease eat?

Kidney diets restricted in phosphorus are recommended from stage 2 in most cats. Ask your vet before changing food [1].

Are cats in pain with kidney failure?

CKD itself is not usually painful, but nausea, dehydration and advanced disease make cats feel unwell. Treatment aims to keep them comfortable [1].

Sources

  1. Sparkes AH et al. ISFM Consensus Guidelines on the Diagnosis and Management of Feline Chronic Kidney Disease. J Feline Med Surg. 2016;18(3):219-239. doi.org/10.1177/1098612X16631234
  2. Acierno MJ et al. ACVIM consensus statement: guidelines for the identification, evaluation, and management of systemic hypertension in dogs and cats. J Vet Intern Med. 2018;32(6):1803-1822. doi.org/10.1111/jvim.15331
  3. International Renal Interest Society (IRIS). IRIS Staging of CKD, modified 2026. iris-kidney.com/s/IRIS_staging_guidelines-2026.pdf
  4. Boyd LM et al. Survival in cats with naturally occurring chronic kidney disease (2000-2002). J Vet Intern Med. 2008;22(5):1111-1117. doi.org/10.1111/j.1939-1676.2008.0163.x

Laboratory methods and reference intervals vary. This article explains; it does not diagnose. For a decision about your pet, use the original report and talk to your veterinarian. Our editorial policy.

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