Table 4.

Predictors of 28-day mortality using Cox proportional hazards regression analysis

	Univariate		Multivariate
Variables	HR (95% CI)	P value	HR (95% CI)	P value
Age (per 10 years)	0.97 (0.79-1.20)	0.791
Sex (female)	0.76 (0.40-1.45)	0.401
SIRS†	1.22 (0.48-3.16)	0.675
Sepsis†	3.54 (1.42-8.82)	0.007
RIFLE category*	--	0.381
ln SOFA - renal variable (per 1 SD ↑)	1.05 (0.66-1.67)	0.846
LOS before start of RRT (per day)	1.00 (0.96-1.04)	0.889
ln APACHE II score (per 1 SD ↑)	1.72 (1.15-2.56)	0.008
ln total SOFA score (per 1 SD ↑)	1.79 (1.28-2.50)	<0.001	1.62 (1.17-2.25)	0.004
ln CRP (per 1 SD ↑)	1.71 (1.13-2.58)	0.012
ln cystatin C (per 1 SD ↑)	1.07 (0.77-1.50)	0.679
ln NGAL (per 1 SD ↑)	1.79 (1.28-2.51)	<0.001	1.60 (1.15-2.23)	0.005

Estimated hazard ratios (HR), 95% confidence intervals (CI), and P values were calculated by Cox regression analyses (backward elimination). Variables found to be statistical significant at a P value of less than 0.1 in the univariate model were included into the multivariate model using stepwise backward elimination. A two-sided P value of less than 0.05 was considered statistically significant in the multivariate model. Variables that were not normally distributed were log transformed; hazard ratios refer to 1 standard deviation (SD) in the log scale in these variables. † For SIRS and sepsis, the non-SIRS/sepsis group was set as the reference group. *HR (95% CI) for categorical variables is only displayed in case of multivariate significance.

APACHE II score = Acute Physiology And Chronic Health Evaluation score; CRP = C reactive protein; LOS = length of stay in the intensive care unit; NGAL = neutrophil gelatinase-associated lipocalin; RIFLE = a newly developed international consensus classification for acute kidney injury, that defines three grades of severity - risk (class R), injury (class I) and failure (class F); RRT = renal replacement therapy; SOFA = Sequential Organ Failure Assessment score; SIRS = systemic inflammatory response syndrome.