IRIS staging
The IRIS stages of kidney disease in cats, gently explained.
Vets around the world use the International Renal Interest Society (IRIS) system to describe chronic kidney disease in cats. Here’s what each stage generally means, and what it doesn’t.
Before you read
These are reference ranges, not a stage. Only your vet can stage CKD — in a cat that is clinically stable and well hydrated, using results from at least two occasions and the whole clinical picture. Staging is done once a cat is stable and well hydrated, usually after at least two tests, and considers urine tests, blood pressure and the whole cat.
Stage 1 · Non-azotemic
Creatinine is in the normal range, but there is other evidence of kidney change — such as poorly concentrated urine, abnormal imaging, protein in the urine, or a persistently raised SDMA. Many cats live a long time at this stage.
Read about Stage 1 →2Stage 2 · Mild
Creatinine is mildly raised. Many cats have few or no outward signs, though some drink and urinate more. This is often when diet changes and regular monitoring begin.
Read about Stage 2 →3Stage 3 · Moderate
Kidney values are moderately raised and cats may start to show signs such as reduced appetite, weight loss, nausea or dehydration. Supportive care — fluids, anti-nausea medicine, phosphorus control — often becomes part of daily life.
Read about Stage 3 →4Stage 4 · Severe
Kidney values are markedly raised and cats are more likely to feel unwell. Care focuses on comfort, appetite, hydration and quality of life, in close partnership with your vet.
Read about Stage 4 →IRIS reference values for cats
| Stage | Creatinine mg/dL (µmol/L) | SDMA µg/dL | Phosphorus target mg/dL |
|---|---|---|---|
| Stage 1 | < 1.6 (< 140) | < 18 | — |
| Stage 2 | 1.6 – 2.8 (140 – 250) | 18 – 25 | 2.5 – 4.5 |
| Stage 3 | 2.9 – 5.0 (251 – 440) | 26 – 38 | 2.5 – 5 |
| Stage 4 | > 5.0 (> 440) | > 38 | 2.5 – 6 |
Source: IRIS Staging of CKD (modified 2023) — iris-kidney.com; phosphate targets: 2026 iCatCare consensus guidelines. Please check iris-kidney.com for the latest version.
Substages
IRIS also describes every cat with CKD by urine protein and blood pressure, at any stage.
| UPC | Substage |
|---|---|
| < 0.2 | Non-proteinuric |
| 0.2 – 0.4 | Borderline proteinuric |
| > 0.4 | Proteinuric |
| Systolic (mmHg) | Substage |
|---|---|
| < 140 | Normotensive |
| 140 – 159 | Prehypertensive |
| 160 – 179 | Hypertensive |
| ≥ 180 | Severely hypertensive |
IRIS staging FAQ
What are the IRIS stages of kidney disease in cats?
IRIS describes chronic kidney disease in four stages, based mainly on blood creatinine and SDMA in a stable cat: Stage 1 (non-azotemic), Stage 2 (mild), Stage 3 (moderate) and Stage 4 (severe). Cats are also substaged by urine protein (UPC) and blood pressure.
My cat’s creatinine and SDMA point to different stages. Which one is right?
This is common. Creatinine is affected by muscle mass and SDMA is not, so they can disagree, especially in thin or older cats. Your vet considers both, plus urine tests and your cat’s overall health.
Can a cat move back to an earlier stage?
Values can improve, for example once a cat is rehydrated or another illness is treated, which is one reason IRIS asks for stable, repeated results before staging. Chronic kidney damage itself usually doesn’t reverse, but many cats stay stable for a long time.
KidneyPaw explains lab values for information only. It does not diagnose, stage or treat. Always discuss results and any changes in care with your veterinarian.
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