Chronic kidney disease (CKD) in cats is managed on a 3-month cycle: 4 markers, 1 table, and 2 escalation triggers written down in advance. The stage rarely changes on its own between visits; what changes is the trend inside a stage, and that is what the 3-month interval exists to catch.
IRIS staging, in numbers
The International Renal Interest Society (IRIS) stages CKD on fasting creatinine, confirmed on at least 2 samples in a hydrated cat, with SDMA as a supporting marker. Stage 1 is creatinine under 1.6 mg/dL with poor urine concentration and SDMA under 18. Stage 2 is 1.6 to 2.8 mg/dL. Stage 3 is 2.9 to 5.0 mg/dL. Stage 4 is above 5.0 mg/dL. Staging is a snapshot; treatment is driven by the trend, the protein level in urine and blood pressure.
The staging table
| IRIS stage | Creatinine (mg/dL) | SDMA (ug/dL) | Typical findings | Review interval |
|---|---|---|---|---|
| 1 | under 1.6 | under 18 | USG under 1.035, no azotemia | every 6 months |
| 2 | 1.6-2.8 | 18-35 | mild azotemia, weight stable | every 3 months |
| 3 | 2.9-5.0 | 36-54 | weight loss 5 percent or more, phosphate rising | every 8-12 weeks |
| 4 | above 5.0 | above 54 | vomiting, weakness, potassium under 3.5 | every 4-6 weeks |
Sub-staging runs in parallel and matters as much as the number: urine protein to creatinine ratio (UPC) under 0.2 is normal, 0.2 to 0.4 is borderline, above 0.4 is proteinuric. Systolic blood pressure under 150 mmHg is normal, 150 to 159 is borderline, 160 to 179 is hypertensive, and 180 or higher is severely hypertensive and needs treatment the same week.
4 markers, every 3 months
Creatinine plus SDMA shows where the cat sits and which direction it is moving. UPC shows whether protein is leaking, which predicts progression better than creatinine alone in stage 1 and 2. Systolic blood pressure shows the damage that CKD causes outside the kidney, including retinal detachment and stroke. Potassium shows the depletion that stage 3 and 4 cats develop, with weakness and a dropped head as late signs. Weight and body condition score are recorded at the same visit, because a 5 percent loss over 3 months is a trigger on its own even when creatinine is flat.
Why 3 months and not 6
Creatinine moves slowly enough that a 6-month gap can hide 0.6 mg/dL of change, which is most of a stage. Three months gives 4 data points a year, enough to separate a trend from a single bad day, and it matches the interval at which phosphate and potassium drift in stage 2 to 3 cats. A cat that is dehydrated, has a urinary infection or has just been started on a renal diet should be rechecked at 4 to 6 weeks first, then moved onto the 3-month cycle once 2 consecutive sets of results are stable.
The 2 escalation triggers
Trigger 1 is stage movement: creatinine rising by 0.5 mg/dL or more within 3 months, or SDMA rising past 18, 35 or 54, or any single jump of 25 percent in creatinine with matching clinical signs. Trigger 2 is target failure on the non-renal markers: UPC above 0.4, systolic blood pressure at 160 mmHg or higher on 2 readings 10 minutes apart, potassium under 3.5 mmol/L, or phosphate above 5.0 mg/dL in stage 3 despite a renal diet. Either trigger moves the cat from 3-month follow-up to a 4 to 6 week recheck plus a treatment review, and trigger 2 also means a conversation about a specialist or an internal medicine referral.
Monitoring table for the visit
| Marker | Reference | Escalate at | Action | Recheck |
|---|---|---|---|---|
| Creatinine | 0.8-2.4 mg/dL | rise of 0.5 mg/dL in 3 months | hydration check, stage review | 4 weeks |
| SDMA | under 14 ug/dL | 35 or above | repeat in 14 days | 2 weeks |
| UPC | under 0.2 | above 0.4 | protein review, blood pressure | 4 weeks |
| Systolic BP | 120-160 mmHg | 160 mmHg or higher | repeat 2 readings, treatment review | 1-2 weeks |
| Potassium | 3.5-5.8 mmol/L | under 3.5 mmol/L | supplement review | 2 weeks |
| Phosphate | 2.7-4.6 mg/dL | above 5.0 mg/dL | diet and binder review | 4 weeks |
Between visits: what the owner tracks
Weigh the cat every 2 weeks on the same scale and write the number down; 0.2 kg on a 4 kg cat is 5 percent, and it is the earliest sign most owners can measure at home. Count water intake roughly by the bowl, note urine clumps per day (a cat producing 4 large clumps a day is drinking more than before), and record appetite as a fraction of the usual ration: 3/4 of normal for 3 days is a phone call, 1/2 for 2 days is a visit. Vomiting more than 2 times a week, mouth ulcers, or a coat that stops being groomed all belong in the same log.
When to call the vet
Same day for not eating for 24 hours, vomiting more than 3 times in 24 hours, a cat that cannot stand, seizures, breathing with the mouth open, or no urine for 12 hours. Within 48 hours for weight loss of 5 percent, potassium under 3.5 mmol/L on a home-adjacent lab, sudden blindness, or a cat that stops grooming. Within 7 days for a UPC or blood pressure result above target, or a creatinine rise of 0.5 mg/dL since the last check. A cat in stage 4 with vomiting and weakness is a hospital case, not a wait-and-see case.
Raising or lowering the level of care
- Raise to hospital: stage 4 with vomiting, potassium under 3.5 mmol/L with weakness, systolic pressure 180 mmHg or higher, or 12 hours without urine.
- Raise to a 4-6 week recheck: any stage movement, UPC above 0.4, phosphate above 5.0 mg/dL, or 5 percent weight loss.
- Hold the 3-month cycle: 2 consecutive stable sets, UPC under 0.2, pressure under 150 mmHg, weight within 3 percent.
- Lower to 6 months: stage 1 with stable SDMA under 18 and normal pressure for 12 months.
What to bring to the next visit
- Twelve months of creatinine and SDMA values on one line, with dates.
- A weight log, 2 readings a month, same scale.
- A 7-day food and water record, with grams and milliliters.
- The current medication list, including phosphate binders and any supplement.
- Blood pressure readings with the cuff size used, since a wrong cuff shifts the number by 10 to 20 mmHg.
Renal diets, phosphate binders, potassium supplements and anti-emetics are all by veterinary prescription, and the dose depends on the latest potassium, phosphate and creatinine values, so nothing here should be started at home. A cat with CKD and sore joints needs the low-impact assessment in the multimodal pain plan, because untreated pain suppresses appetite and looks like progression. Parasite control still matters in an older cat, and the flea allergy plan explains why a flea burden can crash a stable kidney cat. Any suspected toxin exposure goes to the toxin lookup before anything else, since a kidney cat has no reserve.
Terms mentioned in this article
Frequently asked
Does a stable stage 2 cat need blood work every 3 months?
Yes, if the cat is stage 2 or higher. Three months is the interval at which a 0.5 mg/dL creatinine change, a UPC crossing 0.4 or a phosphate drift becomes visible before the cat looks sick. The bill for a creatinine, SDMA, UPC, potassium and blood pressure check is usually $120 to $220, and catching one stage boundary early is worth several of those panels. Stage 1 cats with stable SDMA can drop to every 6 months.
Is SDMA better than creatinine?
Neither replaces the other. SDMA rises with roughly 40 percent kidney function loss and is less affected by muscle mass, which helps in a thin older cat, while creatinine is the number the IRIS stages are built on and is what most treatment decisions are indexed to. Use both: SDMA flags early change, creatinine sets the stage, and a rise in either one with matching signs triggers a recheck in 2 to 4 weeks.
When does protein in the urine become serious?
A UPC under 0.2 is normal, 0.2 to 0.4 is borderline and should be repeated in 4 to 6 weeks, and above 0.4 is proteinuric and worth treating, usually with a blood pressure check and a prescribed medication. Proteinuria above 0.4 predicts faster progression in stage 1 and 2 cats, so it is one of the 2 escalation triggers and moves follow-up from 3 months to 4 to 6 weeks.