AKI Staging Calculator

Classify Acute Kidney Injury (AKI) severity using KDIGO criteria. Enter serum creatinine values and/or urine output to determine AKI stage (1-3). Compliant with NICE AKI guidelines (NG148).

Important Clinical Disclaimer: The AKI Staging Calculator is intended for use by qualified healthcare professionals only. It is for educational and informational purposes and should not replace clinical judgement. Always interpret results alongside the full clinical picture and follow your local guidelines and protocols.
AKI Staging Parameters
Patient Demographics
For baseline estimation if unknown
Serum Creatinine Values
Latest serum creatinine value
Stable value from past 3-12 months
For detecting ≥26 µmol/L rise in 48h
Urine Output (optional)
Additional Information
About KDIGO AKI Staging

The KDIGO (Kidney Disease: Improving Global Outcomes) criteria are the current international standard for defining and staging acute kidney injury.

Key features:

  • Unified RIFLE and AKIN criteria
  • Based on creatinine rise AND/OR urine output
  • Three stages of increasing severity
  • Endorsed by NICE (NG148) and Renal Association
AKI is a medical emergency. Early recognition and management improves outcomes. Use the NHS AKI Warning Stage algorithm for electronic alerts.
KDIGO AKI Staging Criteria
Stage Serum Creatinine Urine Output
1 ≥26 µmol/L rise in 48h
or 1.5-1.9× baseline 		<0.5 mL/kg/h for 6-12h
2 2.0-2.9× baseline <0.5 mL/kg/h for ≥12h
3 ≥3× baseline
or ≥354 µmol/L
or RRT initiated 		<0.3 mL/kg/h for ≥24h
or anuria ≥12h
The highest stage from either criterion applies. Only one criterion needs to be met for staging.
AKI Risk Factors (NICE)

Chronic risk factors:

  • Age ≥65 years
  • Pre-existing CKD (eGFR <60)
  • Diabetes mellitus
  • Heart failure
  • Liver disease
  • Cognitive impairment/dementia

Acute risk factors:

  • Sepsis or severe infection
  • Hypovolaemia/dehydration
  • Nephrotoxic drugs (NSAIDs, ACEi, ARBs, aminoglycosides, contrast)
  • Urinary tract obstruction
  • Major surgery
NHS AKI Warning Stage

The NHS uses automated AKI Warning Stages based on creatinine changes:

  • Stage 1: Creatinine rise ≥26 µmol/L in 48h or ≥1.5× lowest in 7 days
  • Stage 2: Creatinine ≥2× lowest in 7 days
  • Stage 3: Creatinine ≥3× lowest in 7 days or ≥354 µmol/L (with rise ≥26 µmol/L in 48h or ≥1.5× in 7 days)

These automated alerts may differ slightly from clinical KDIGO staging which includes urine output.

AKI Management by Stage (NICE NG148)

Stage 1

Actions within 6 hours:

  • Identify and treat cause
  • Review medications (stop nephrotoxins)
  • Optimise fluid status
  • Monitor urine output
  • Recheck creatinine within 24-48h
  • Consider urinary catheter if obstruction suspected

Many Stage 1 AKI cases resolve with supportive care.

Stage 2

Additional actions:

  • Senior clinical review
  • Consider renal ultrasound
  • More frequent creatinine monitoring
  • Consider nephrology referral
  • Assess for complications (acidosis, hyperkalaemia, fluid overload)
  • Consider critical care if deteriorating

Higher risk of progression and complications.

Stage 3

Urgent actions:

  • Urgent nephrology referral
  • Consider RRT (dialysis)
  • Critical care input if indicated
  • Manage complications:
    • Hyperkalaemia (ECG, treatment)
    • Metabolic acidosis
    • Fluid overload
    • Uraemic symptoms
  • Daily or more frequent creatinine

High mortality risk. May need RRT.

AKI Investigation Algorithm

Blood Tests
  • Urea and electrolytes (check K+)
  • Bicarbonate/venous blood gas
  • Full blood count
  • Bone profile (calcium, phosphate)
  • Liver function tests
  • CRP, lactate if sepsis suspected
  • CK if rhabdomyolysis suspected
  • Consider myeloma screen in elderly
Urine Tests
  • Urinalysis (dipstick)
  • Urine microscopy if glomerulonephritis suspected
  • Urine protein:creatinine ratio
  • Urine sodium (for FENa calculation)
Imaging
  • Renal ultrasound (obstruction, size, hydronephrosis)
  • Bladder scan if retention suspected

Frequently Asked Questions

These are successive classification systems for acute kidney injury:

  • RIFLE (2004): First consensus definition - Risk, Injury, Failure, Loss, End-stage. Used percentage changes in creatinine/GFR and urine output.
  • AKIN (2007): Modified RIFLE with absolute creatinine rise criterion (≥26.5 µmol/L in 48h) and 48-hour window for staging.
  • KDIGO (2012): Current standard. Combined RIFLE and AKIN, allowing both 48-hour and 7-day windows. Added RRT initiation as Stage 3 criterion.

Use KDIGO criteria - they are the current international standard endorsed by NICE and renal associations worldwide.

Yes, absolutely. Acute-on-chronic kidney disease (AKI on CKD) is common and associated with worse outcomes. Key points:

  • CKD is a major risk factor for AKI
  • Use the patient's stable CKD creatinine as baseline (not a normal value)
  • The same KDIGO staging criteria apply
  • Recovery may be incomplete, with further decline in baseline function
  • These patients are at higher risk of progressing to end-stage renal disease

NICE recommends urgent nephrology referral for:

  • AKI Stage 3
  • Suspected intrinsic renal disease (glomerulonephritis, vasculitis, interstitial nephritis)
  • No clear cause identified
  • Inadequate response to treatment
  • Renal transplant recipients
  • Complications requiring RRT consideration:
    • Refractory hyperkalaemia (K+ >6.5 despite treatment)
    • Severe metabolic acidosis (pH <7.15)
    • Refractory pulmonary oedema
    • Uraemic complications (pericarditis, encephalopathy)

Use both if available - the higher stage from either criterion applies. However:

  • Creatinine criteria are used most often as they're readily available
  • Urine output criteria are most useful in ICU with hourly monitoring
  • Urine output can be affected by diuretics, fluid intake, and catheter issues
  • Creatinine is a lagging indicator - urine output may detect AKI earlier
  • In community/ward settings, creatinine alone is often sufficient

The NHS AKI Warning Stage algorithm uses creatinine only for automated detection.

Review and consider stopping the "DAMN" or "SADMAN" drugs:

  • Diuretics (especially in hypovolaemia)
  • ACE inhibitors / ARBs
  • Metformin (risk of lactic acidosis)
  • NSAIDs
  • SGLT2 inhibitors

Also review:

  • Aminoglycosides (gentamicin)
  • Contrast agents (avoid or hydrate)
  • Any renally-excreted drugs (dose adjust)

Temporary cessation during acute illness is often appropriate - restart when recovered ("sick day rules").

Disclaimer

This calculator is provided for educational and informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment.

  • Always seek the advice of a qualified healthcare provider with any questions regarding a medical condition.
  • Never disregard professional medical advice or delay seeking it because of information from this tool.
  • Clinical decision-making should always incorporate the full clinical context, patient preferences, and local protocols.
  • The creators of this tool accept no liability for decisions made based on its output.

If you are a patient: please discuss any results with your healthcare provider. This tool is designed for use by medical professionals and may not be appropriate for self-assessment.

References

  1. KDIGO Clinical Practice Guideline for Acute Kidney Injury. Kidney Int Suppl. 2012;2(1):1-138. https://kdigo.org/guidelines/acute-kidney-injury/
  2. NICE. Acute kidney injury: prevention, detection and management (NG148). 2019. https://www.nice.org.uk/guidance/ng148
  3. NHS England. Algorithm for detecting Acute Kidney Injury (AKI) based on serum creatinine changes. 2014. https://www.england.nhs.uk/akiprogramme/
  4. UK Renal Association. Clinical Practice Guidelines: Acute Kidney Injury. https://ukkidney.org/
  5. Levey AS, et al. A new equation to estimate glomerular filtration rate. Ann Intern Med. 2009;150(9):604-612.
  6. Mehta RL, et al. Acute Kidney Injury Network: report of an initiative to improve outcomes in acute kidney injury. Crit Care. 2007;11(2):R31.
  7. Bellomo R, et al. Acute renal failure - definition, outcome measures, animal models, fluid therapy and information technology needs: the Second International Consensus Conference of the Acute Dialysis Quality Initiative (ADQI) Group. Crit Care. 2004;8(4):R204-R212.