IRIS CKD Guide

Start with stable, diagnosed CKD

IRIS staging starts after chronic kidney disease has been diagnosed. An increased creatinine or SDMA value alone does not diagnose CKD.

Interpret the results alongside the history, physical examination, urinalysis, imaging, urine concentrating ability, proteinuria, and previous laboratory findings. Base staging on fasting creatinine, SDMA, or preferably both, measured on at least two occasions in a stable and adequately hydrated patient.

In early CKD, supporting findings may include rising creatinine or SDMA over time, persistent SDMA above 14 µg/dL, renal proteinuria, abnormal renal imaging, or other evidence of kidney disease. Interpret each finding as part of the complete clinical picture.

Step 1: choose the right species and unit

Creatinine ranges differ between dogs and cats. Use the table that matches both the species and the unit reported by the laboratory. Near a stage boundary, use the original unit table instead of converting the result.

A patient can have Stage 1 CKD even when creatinine is inside the laboratory reference interval, but only when other evidence of kidney disease is present.

Step 2: add SDMA when available

Creatinine and SDMA are surrogate markers of glomerular filtration. Using both can give more context than relying on one result alone. Creatinine is affected by muscle mass, while SDMA is generally less affected by a loss of lean body mass.

IRIS SDMA guidance is based on published work using IDEXX SDMA methodology. Results from other methods may not be directly equivalent.

Step 3: slow down when creatinine and SDMA disagree

Creatinine and SDMA can place the same patient in different stages. That does not automatically mean one value is wrong.

Step 4: add proteinuria substage

The primary stage does not describe the whole case. UPC adds a separate proteinuria substage. Standard urine dipsticks can be insensitive, so use a quantitative test such as UPC or an appropriate species-specific albuminuria assay.

Before classifying the patient, exclude pre-renal and postrenal causes of proteinuria. Do not assign a renal proteinuria substage from a sample affected by urinary tract inflammation, hemorrhage, dysproteinemia, or another nonrenal source. Base the substage on at least two urine samples collected over at least two weeks. Reassess persistent borderline proteinuria within about two months.

Step 5: add blood pressure substage

Systolic blood pressure is the second IRIS substage. Let the patient acclimatize, take multiple readings, and confirm the category across repeated visits when possible.

Persistence depends on species and severity. In dogs without target organ damage, IRIS treatment recommendations assess SBP 160 to 179 mmHg over 2 to 4 weeks, and severe hypertension over 1 to 2 weeks. For cats without target organ damage, repeat measurements over 1 to 2 weeks, using a shorter interval as pressure rises. If target organ damage is present, do not delay treatment to demonstrate persistence. Some dog breeds, especially sighthounds, may have higher expected blood pressure; use breed-specific reference ranges when available.

For cats: the stage is only the first layer

The 2026 iCatCare guidelines help you assess phosphorus, FGF23, calcium, anaemia, and concurrent hypertension and proteinuria after staging. These findings can change management without changing the primary IRIS stage. You do not need every marker in every cat.

1. Look at phosphorus before FGF23

FGF23 can help guide phosphate restriction when interpreted alongside phosphorus and azotaemia status. For azotaemic cats, iCatCare lists serum phosphorus target ranges of 2.5 to 4.5 mg/dL in Stage 2, 2.5 to 5.0 mg/dL in Stage 3, and 2.5 to 6.0 mg/dL in Stage 4. Aim below the upper limit for the stage. If phosphorus is outside target, address it before using FGF23 to guide further restriction.

Use the early/non-azotaemic pathway only when phosphorus is below 4.5 mg/dL. In azotaemic CKD, introduce a veterinary renal diet and reassess after 4 to 6 weeks; use FGF23 once phosphorus is within target.

Stage 2 does not automatically mean azotaemic CKD. Use the laboratory creatinine reference interval to select the pathway, as Vetool does. Review calcium, anaemia, and inflammation before acting on an elevated FGF23 result.

2. Check calcium before increasing phosphate restriction

Measure ionised calcium when possible and interpret it against the laboratory reference interval. Total calcium may not reflect ionised calcium. Hypercalcaemia can be present at diagnosis or develop after starting a phosphate-restricted renal diet. If calcium is high, review the diet, phosphate binders, and other causes before increasing restriction.

3. Address hypertension, then reassess proteinuria

Hypertension can increase proteinuria. In a cat with SBP of 160 mmHg or higher and UPC above 0.4, address hypertension and reassess UPC once SBP is below 160 mmHg before adding separate antiproteinuric treatment. Telmisartan may be an appropriate initial antihypertensive; monitor for hypotension when combining agents.

After starting an ARB or ACE inhibitor, reassess clinical signs, SBP, creatinine, and potassium in 1 to 2 weeks. A creatinine rise above 25 to 30% warrants treatment review. Assess the effect on UPC at about 4 weeks.

4. Keep PCV/HCT in the picture

Consider active management of CKD-associated anaemia when PCV is below 25%, or remains at 25 to 28% for more than one month. Assess the cause and the benefits and risks of treatment for the individual cat. Anaemia affects management, but does not change the IRIS stage.

Step 6: reassess stage and substages over time

IRIS staging is not a permanent label. Update the classification when creatinine, SDMA, UPC, blood pressure, treatment, or the patient's clinical condition changes. If antihypertensive or antiproteinuric treatment changes the current result, document the new substage and note that the patient is receiving treatment. In cats, phosphorus, calcium, PCV/HCT, and other relevant markers may change what needs attention even when the primary stage stays the same.

Where CKD staging usually drifts

The staging tables are short. Most mistakes happen in the context around them.

What the final classification should include

A complete IRIS CKD classification should include the primary IRIS stage, creatinine basis, SDMA basis when available, proteinuria substage, blood pressure substage, relevant treatment status, and any context that changes interpretation.

Example: IRIS CKD Stage 2, borderline proteinuric, severely hypertensive. After treatment, the same patient may be reclassified using current UPC and blood pressure values, with treatment status documented.

For cats, record muscle condition, PCV/HCT, phosphorus, azotaemia status, ionised calcium, and FGF23 when available. These results add management context to the stage and substages.