Table 1. Summary of NHS England AKI algorithm.

AKI Criteria	Definition for AKI (one of the three)
Criterion 1	Serum creatinine ≥1.5 times higher than the median of all creatinine values 8–365 days ago
Criterion 2	Serum creatinine ≥1.5 times higher than the lowest creatinine within 7 days
Criterion 3	Serum creatinine >26 μmol/L higher than the lowest creatinine within 48 hours
AKI Stage	Classification Requirements
Stage 1	Rise in creatinine of >26 μmol/L; or index/reference ≥1.5 and <2
Stage 2	Index/reference ≥2 and <3
Stage 3	Index/reference ≥3; or ≥1.5 and index creatinine >354 μmol/L (or 3 times the upper reference interval if age <18)

AKI can be diagnosed if any one of three criteria are met. Staging is based on a comparison of a serum creatinine (index) with a reference test. Where a creatinine is outside the reference range but a previous creatinine within one year is unavailable, the test is “flagged” abnormal (with chronicity unknown).