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Endocrine & Metabolic · Clinical background

IRIS CKD staging

International Renal Interest Society staging for chronic kidney disease in dogs and cats. Stage 1–4 from creatinine and SDMA, substaged by UPC (proteinuria) and systolic blood pressure.

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Clinical background

The International Renal Interest Society (IRIS) staging system is the global standard for classifying chronic kidney disease severity in dogs and cats. It exists because CKD is a continuum, and clinically meaningful decisions (when to start treatment, which treatment, how aggressively to monitor) depend on where on that continuum the patient sits. The staging system, last updated in 2023, is built around a fasting blood creatinine and SDMA, then substaged by proteinuria (UPC) and systolic blood pressure.

Why both creatinine and SDMA

Creatinine has been the standard renal biomarker for decades, but it is influenced by muscle mass and only rises after roughly 75% of nephron function has been lost. SDMA (symmetric dimethylarginine) is less muscle-mass dependent and rises earlier in the disease course, often before creatinine becomes abnormal. The 2019 IRIS update incorporated SDMA as a complementary marker. When both are available, IRIS recommends staging at the worse of the two values.

This calculator computes both stages and reports the higher of them as the final stage, which is the IRIS-recommended approach.

The two staging requirements

IRIS staging applies only after CKD has been diagnosed. That diagnosis itself requires demonstrating that renal abnormalities have been present for at least three months, and that the patient is hydrated and stable when tested. Staging an azotemic patient who is dehydrated or in active prerenal injury produces a falsely advanced stage. Repeat the labs in 2–4 weeks once the patient is stable; if the stage shifts, the higher (worse) stage is generally retained as a precaution.

Stage descriptions in clinical terms

Stage 1. Non-azotemic; the diagnosis rests on persistent renal proteinuria, abnormal renal imaging or palpation, persistently dilute urine without another cause, or persistently elevated SDMA. Clinical signs are typically absent. Most patients in this stage are identified incidentally during senior wellness panels.

Stage 2. Mild renal azotemia. The lower end of this stage may not even exceed the laboratory’s reference interval, especially in larger or more muscular dogs. Clinical signs are typically absent or very mild (mild PU/PD, subtle weight loss). The 2019 IRIS update expanded Stage 2 in dogs to better match clinical decision-making.

Stage 3. Moderate renal azotemia. Many patients show systemic signs at this point: polyuria/polydipsia, weight loss, decreased appetite, vomiting in some, lethargy. The 2019 update splits this stage into early and late Stage 3 because treatment intensity differs across that range.

Stage 4. Severe renal azotemia with marked uremic complications: significant inappetence, vomiting, lethargy, oral ulcers, neurologic signs in some. Aggressive supportive care is generally required and prognosis is guarded.

The substages and why they matter

UPC and systolic blood pressure are not just risk markers; they are independent therapeutic targets, with specific thresholds for intervention. Proteinuric patients (UPC > 0.5 in dogs, > 0.4 in cats) benefit from RAAS inhibition (ACE inhibitor, telmisartan) regardless of stage. Hypertensive patients (SBP ≥ 160 mmHg, ideally confirmed across multiple visits) benefit from antihypertensive therapy because elevated systemic pressure accelerates glomerular damage and increases the risk of target-organ damage to eyes, heart, and brain.

A patient can be Stage 2 with significant proteinuria and hypertension and need more aggressive management than a Stage 3 patient with neither. The stage drives the broad supportive-care plan; the substages drive the specific drug interventions.

How to use the calculator

  1. Enter creatinine (and SDMA if available, strongly recommended). The calculator returns the IRIS stage at the worse of the two markers.
  2. Enter UPC if measured. The calculator returns the proteinuric substage classification.
  3. Enter systolic blood pressure if measured. The calculator returns the hypertensive substage and target-organ damage risk band.

The output is intended for quick reference. Formal IRIS staging requires confirming creatinine and SDMA on at least two occasions in a hydrated, stable patient; the calculator gives a single-time-point snapshot.

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