Table 3.

Incidence rates and hazard ratios of ICU mortality for AKI stage ≥ 2 vs no AKI stage ≥ 2 across different criteria.

KDIGO stage ≥ 2 criterion	Incidence rate of ICU mortality (estimated number of ICU deaths per 1,000 patient days at risk)1		Unadjusted cause-specific hazard ratio of ICU mortality2 (95% CI)	Concordance index3	Adjusted cause-specific hazard ratio of ICU mortality4 (95% CI)	Concordance index3
	Patient days with AKI	Patient days without AKI
Cox proportional hazards models including a single criterion as predictor
SCrea	31.3	16.1	2.11 (1.85–2.42)	0.568	1.81 (1.56–2.09)	0.663
UO-1	27.2	12.6	3.00 (2.55–3.54)	0.593	2.59 (2.18–3.09)	0.680
UO-2	36.6	14.1	3.21 (2.79–3.69)	0.597	2.83 (2.44–3.28)	0.688
SCrea-UO-1	26.5	12.1	2.85 (2.43–3.34)	0.604	2.54 (2.14–3.02)	0.683
SCrea-UO-2	32.8	13.2	2.93 (2.57–3.35)	0.615	2.62 (2.27–3.04)	0.695
Cox proportional hazards model including both SCrea and UO-1 as predictors
SCrea			1.67 (1.46–1.92)	0.624	1.48 (1.27–1.71)	0.693
UO-1			2.63 (2.22–3.11)		2.35 (1.97–2.82)
Cox proportional hazards model including both SCrea and UO-2 as predictors
SCrea			1.35 (1.16–1.57)	0.624	1.18 (1.01–1.39)	0.694
UO-2			2.82 (2.41–3.29)		2.63 (2.23–3.10)

¹Incidence rate ratios only approximate (cause-specific) hazard ratios when the survival distributions in each group both follow an exponential distribution.

²Estimated by an extended Cox model that treats ICU discharge as a censoring event.

³Concordance indices are displayed for the corresponding Cox model whose exponentiated coefficient estimates are displayed in the column on the left hand side.

⁴Estimated by an extended Cox model that treats ICU discharge as a censoring event that additionally incorporates gender, age (binned into 4 categories according to quartiles) and SOFA score at ICU admission (binned into 4 categories according to quartiles). As a reference: the concordance index for a Cox model including only gender, age and SOFA score at ICU admission (excl. AKI criteria) equalled 0.640.

SCrea: serum creatinine > 4.0 mg/dl or > 2 × baseline, where baseline = SCrea-1 whenever available, otherwise SCrea-2, or SCrea-3 (when neither SCrea-1 nor SCrea-2 are available) with Screa-1 defined as baseline Screa measurement as manually entered in ICIS by the treating physician at ICU admission; Screa-2 defined as the lowest pre-ICU measurement up to 365 days before ICU admission as extracted from the lab information system; Screa-3 defined as a back-calculated baseline Screa using the simplified 4-variable Modification of Diet in Renal Disease (MDRD) Study equation assuming an estimated glomerular filtration rate (eGFR) of 75 ml/min/1.73 m² for every patient³⁰; UO-1: total UO during the last 12-h period was ≤ 6 ml/kg; UO-2: total UO during each of the last 12 consecutive 1-h periods was ≤ 0.5 ml/kg; SCrea-UO-1: AKI stage ≥ 2 according to either the SCrea criterion or the UO-1 criterion; SCrea-UO-2: AKI stage ≥ 2 according to either the SCrea criterion or the UO-2 criterion. An extended version of th table is included as Supplementary Table 2.