IRIS CKD Staging Chart for Cats (Stages 1 to 4)
The IRIS chronic kidney disease staging chart for cats: creatinine and SDMA ranges for Stages 1 to 4, plus substaging by urine protein and blood pressure.
Quick answer: The International Renal Interest Society (IRIS) stages feline chronic kidney disease in four levels using fasting blood creatinine and SDMA in a stable, well-hydrated cat. Stage 1 is nonazotemic (creatinine under 1.6 mg/dL, SDMA under 18), Stage 2 is mild azotemia (1.6 to 2.8 mg/dL), Stage 3 is moderate (2.9 to 5.0 mg/dL), and Stage 4 is severe (above 5.0 mg/dL). Each stage is then substaged by urine protein (UPC) and by blood pressure.
IRIS CKD Staging Chart for Cats
Staging is based on a fasting blood sample taken when your cat is stable and well hydrated, and it should be confirmed on at least two measurements taken a week or more apart. SDMA is used alongside creatinine, especially in thin senior cats whose low muscle mass can keep creatinine deceptively low.
| IRIS Stage | Blood Creatinine | SDMA | Description |
|---|---|---|---|
| Stage 1 | Under 1.6 mg/dL (under 140 micromol/L) | Under 18 micrograms/dL | Nonazotemic. Another kidney abnormality is present, such as poor urine concentrating ability, abnormal imaging or palpation, proteinuria, or a rising creatinine trend. |
| Stage 2 | 1.6 to 2.8 mg/dL (140 to 250 micromol/L) | 18 to 25 micrograms/dL | Mild renal azotemia. Many cats show few or no outward signs at this stage. |
| Stage 3 | 2.9 to 5.0 mg/dL (251 to 440 micromol/L) | 26 to 38 micrograms/dL | Moderate renal azotemia. Many cats begin showing increased thirst, weight loss, and reduced appetite. |
| Stage 4 | Above 5.0 mg/dL (above 440 micromol/L) | Above 38 micrograms/dL | Severe renal azotemia. Signs of uremia are common and supportive care needs increase. |
Note on SDMA: in a cat with low body condition, IRIS notes that an SDMA of 25 micrograms/dL or higher may indicate the kidney function of Stage 3, and 45 or higher may indicate Stage 4, even when creatinine reads lower. In those cases your vet may stage the cat at the higher level.
Substaging by Proteinuria (UPC)
Once the main stage is set, IRIS substages cats by their urine protein-to-creatinine ratio (UPC). Higher protein loss is associated with faster decline, so this guides treatment. The ratio is confirmed on repeat samples after ruling out urinary infection and blood in the urine.
| Substage | Urine Protein:Creatinine (UPC) | Meaning |
|---|---|---|
| Nonproteinuric (NP) | Under 0.2 | No significant protein loss. |
| Borderline proteinuric (BP) | 0.2 to 0.4 | Recheck in about 2 months to see if it resolves or progresses. |
| Proteinuric (P) | Above 0.4 | Treatment to reduce protein loss is often recommended. |
Substaging by Blood Pressure
IRIS also substages cats by systolic blood pressure, which reflects the risk of damage to the eyes, brain, heart, and kidneys. High blood pressure is common in feline kidney disease and is treatable, so it is checked regularly.
| Substage | Systolic Blood Pressure | Risk of Future Organ Damage |
|---|---|---|
| Normotensive | Under 140 mmHg | Minimal |
| Prehypertensive | 140 to 159 mmHg | Low |
| Hypertensive | 160 to 179 mmHg | Moderate |
| Severely hypertensive | 180 mmHg or higher | High |
How to Read the Chart
A full IRIS classification combines all three parts. For example, a cat might be described as IRIS Stage 2, proteinuric, severely hypertensive. The main stage tracks how advanced the kidney filtration loss is, while the proteinuria and blood pressure substages flag specific, treatable problems that strongly influence quality of life and survival. This is why a complete kidney workup includes blood (creatinine, SDMA, phosphorus, electrolytes), a urinalysis with UPC, and a blood pressure reading rather than a single number.
These thresholds are published by the International Renal Interest Society (IRIS), a group sponsored to standardize how veterinarians diagnose and treat kidney disease. Laboratory reference ranges can vary slightly, and only your veterinarian can interpret these values in the context of your cat's hydration, history, and physical exam.
Related Reading
- Kidney Disease in Senior Cats - Signs, diet, and day-to-day management this chart complements.
- Hypertension in Senior Cats - High blood pressure that often accompanies kidney disease.
- Old Cat Drinking Lots of Water - One of the earliest signs owners notice.
- Cat Age Calculator - See where your cat falls in their life stage.
This chart is educational and complements, but does not replace, your veterinarian. Staging, substaging, and treatment decisions should always be made by your vet using your cat's full clinical picture.
Frequently Asked Questions
What are the IRIS stages of chronic kidney disease in cats?
The International Renal Interest Society (IRIS) divides feline chronic kidney disease into four stages based on fasting blood creatinine and SDMA in a stable, well-hydrated cat. Stage 1 is nonazotemic (creatinine under 1.6 mg/dL), Stage 2 is mild azotemia (1.6 to 2.8 mg/dL), Stage 3 is moderate (2.9 to 5.0 mg/dL), and Stage 4 is severe (above 5.0 mg/dL). Each main stage is then substaged by urine protein and blood pressure.
What creatinine level is Stage 3 kidney disease in cats?
IRIS Stage 3 chronic kidney disease in cats corresponds to a fasting blood creatinine of 2.9 to 5.0 mg/dL (about 251 to 440 micromol/L), or an SDMA of roughly 26 to 38 micrograms/dL. This is moderate renal azotemia, and many cats begin showing outward signs such as increased thirst, weight loss, and reduced appetite at this stage. Staging should be confirmed on a stable, hydrated patient using more than one measurement.
What is SDMA and why does IRIS use it?
SDMA (symmetric dimethylarginine) is a blood marker of kidney filtration that can rise earlier than creatinine, sometimes detecting kidney disease months sooner. It is also less affected by muscle mass, which matters in thin, older cats whose low muscle can keep creatinine falsely low. IRIS uses SDMA alongside creatinine: if SDMA suggests worse function than creatinine in a thin cat, your vet may stage the cat at the higher level.
What does substaging by proteinuria mean for cats?
After the main stage is set, IRIS substages cats by their urine protein-to-creatinine ratio (UPC). A UPC below 0.2 is nonproteinuric, 0.2 to 0.4 is borderline, and above 0.4 is proteinuric. Proteinuria is linked to faster kidney decline and shorter survival, so identifying it guides treatment such as kidney diets and medications that reduce protein loss. The ratio should be confirmed on repeat samples once urinary infection and bleeding are ruled out.
How is blood pressure used in IRIS staging?
IRIS also substages cats by systolic blood pressure to gauge the risk of damage to the eyes, brain, heart, and kidneys. Below 140 mmHg is normotensive (minimal risk), 140 to 159 is prehypertensive (low risk), 160 to 179 is hypertensive (moderate risk), and 180 mmHg or higher is severely hypertensive (high risk). High blood pressure is common with feline kidney disease and is treatable, so it is checked regularly.
Can a cat live a long time with IRIS Stage 2 kidney disease?
Yes. Many cats diagnosed at IRIS Stage 2 live for years with the right care, especially when proteinuria and high blood pressure are controlled and a therapeutic kidney diet is fed. Early stages often progress slowly. Survival varies widely with substage, hydration, phosphorus control, and how consistently the cat is monitored. Catching kidney disease early, before severe azotemia, is one of the strongest factors in a good long-term outcome.
How often should a cat with kidney disease be rechecked?
Recheck frequency depends on the stage. Stable Stage 1 or 2 cats are often rechecked every 6 to 12 months, Stage 3 every 1 to 3 months, and Stage 4 every few weeks to months as needed. Each visit typically includes blood creatinine and SDMA, phosphorus, electrolytes, a urinalysis with UPC, and a blood pressure check. Your veterinarian tailors the interval to how the cat is feeling and how quickly values are changing.
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