KDIGO AKI Stage Calculator

Q: Can AKI stage be assessed from creatinine alone?

Only partially. This calculator uses the creatinine ratio to baseline, but KDIGO stage 1 can also be met by an absolute rise of 0.3 mg/dL or more within 48 hours, which needs two closely timed measurements and is not captured by a single ratio.

Q: What if creatinine and urine output give different stages?

Staging uses whichever criterion gives the higher stage. A patient with a creatinine ratio in the stage 1 range but oliguria meeting stage 2 is classified as stage 2.

Q: Does starting dialysis automatically make it stage 3?

Yes. KDIGO classifies any patient started on renal replacement therapy as stage 3, regardless of the creatinine or urine output at that point.

Q: When is renal replacement therapy indicated in AKI?

Common indications include refractory hyperkalaemia, severe acidosis, fluid overload unresponsive to diuretics, uraemic complications such as pericarditis or encephalopathy, and certain poisonings — the decision is clinical and not determined by stage alone.

Stage acute kidney injury from a creatinine pair and urine output using the KDIGO criteria, taking whichever of the two gives the higher stage.

Last updated 31 Aug 2026

KDIGO AKI Stage

Creatinine + urine output → stage

Current creatinine (mg/dL)

Baseline creatinine (mg/dL)

Urine output

Started renal replacement therapy

Stage 2Example

Creatinine 2.4 mg/dL, baseline 1.0 mg/dL, urine output under 0.5 mL/kg/hr for 6–12 hours, not on RRT

KDIGO AKI staging criteria

Stage 1 — Cr 1.5–1.9× baseline, or UO <0.5 mL/kg/hr for 6–12 h
Stage 2 — Cr 2–2.9× baseline, or UO <0.5 mL/kg/hr for ≥12 h
Stage 3 — Cr ≥3× baseline, or Cr ≥4.0 mg/dL, or UO <0.3 mL/kg/hr for 24 h or anuria for 12 h, or started on RRT
Stage = the higher of the two criteria

Cr ratio: current creatinine ÷ baseline creatinine
UO: urine output per kilogram of body weight per hour, over the stated duration
Not captured here: KDIGO also stages 1 by an absolute rise of ≥0.3 mg/dL within 48 hours — this needs two closely timed values and is not assessed by this single ratio

Worked example

Creatinine 2.4 mg/dL, baseline 1.0 mg/dL, urine output under 0.5 mL/kg/hr for 6–12 hours, not on RRT
Creatinine ratio = 2.4 ÷ 1.0 = 2.4
Not on RRT; urine output has not yet reached the stage 3 threshold
Creatinine ratio of 2.4 meets the stage 2 criterion (≥2), which outranks the stage 1 urine-output finding
→ Stage 2 — staging takes whichever criterion, creatinine or urine output, gives the higher stage

Staging criteria

Whichever criterion — creatinine or urine output — gives the higher stage is the stage that is used.
Stage	Serum creatinine	Urine output
1	1.5 – 1.9× baseline (or ≥0.3 mg/dL rise in 48 h, not assessed here)	< 0.5 mL/kg/hr for 6 – 12 h
2	2.0 – 2.9× baseline	< 0.5 mL/kg/hr for ≥ 12 h
3	≥ 3× baseline, or ≥ 4.0 mg/dL, or started RRT	< 0.3 mL/kg/hr for 24 h, or anuria for 12 h

Reading a KDIGO AKI stage

KDIGO defines acute kidney injury with two parallel sets of criteria, one based on serum creatinine and one on urine output, and stages by whichever gives the higher result. This calculator uses a single creatinine pair — current against a stated baseline — together with a urine output category over the relevant time window, and applies the higher of the two.

An important limitation applies to the creatinine side. KDIGO also defines stage 1 by an absolute rise of 0.3 mg/dL or more within 48 hours, independent of the ratio to baseline. This calculator cannot capture that criterion from a single pair of values, since it needs two creatinine measurements taken close enough together in time, with the timing itself part of the definition. A patient whose creatinine has risen by 0.4 mg/dL over 24 hours, from a baseline low enough that the ratio stays under 1.5, meets KDIGO stage 1 by the absolute-rise rule even though this tool would not flag it. Clinical judgement, and the trend rather than a single snapshot, should always sit alongside the calculated stage.

Urine output criteria are also easy to apply loosely in practice — they require an accurate measured output per kilogram of body weight over a defined duration, not an impression of ‘low output’, and should be based on a catheter or accurate fluid balance chart wherever the stage is being used to guide a management decision.

Frequently asked questions

Can AKI stage be assessed from creatinine alone?

Only partially. This calculator uses the creatinine ratio to baseline, but KDIGO stage 1 can also be met by an absolute rise of 0.3 mg/dL or more within 48 hours, which needs two closely timed measurements and is not captured by a single ratio.

What if creatinine and urine output give different stages?

Staging uses whichever criterion gives the higher stage. A patient with a creatinine ratio in the stage 1 range but oliguria meeting stage 2 is classified as stage 2.

Does starting dialysis automatically make it stage 3?

Yes. KDIGO classifies any patient started on renal replacement therapy as stage 3, regardless of the creatinine or urine output at that point.

When is renal replacement therapy indicated in AKI?

Common indications include refractory hyperkalaemia, severe acidosis, fluid overload unresponsive to diuretics, uraemic complications such as pericarditis or encephalopathy, and certain poisonings — the decision is clinical and not determined by stage alone.

Related calculators

References

KDIGO Clinical Practice Guideline for Acute Kidney Injury. Kidney Int Suppl. 2012;2(1):1–138.
Khwaja A. KDIGO clinical practice guidelines for acute kidney injury. Nephron Clin Pract. 2012;120(4):c179–c184.

Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.