Recently, acute kidney injury defined by small changes in serum creatinine levels was associated with worse short-term outcomes; however, the precision and variability of this association was not fully explored.

Systematic review and meta-analysis.

Hospitalized patients.

MEDLINE and EMBASE databases were searched for observational cohort studies and randomized controlled trials published from 1990 through February 2007 that provided information for small changes in serum creatinine levels.

Small acute changes in serum creatinine levels by absolute and percentage of changes in serum creatinine levels (lower threshold for increase in serum creatinine <0.5 mg/dL or <25%).

Short-term mortality (≤30 days).

Compared with controls, patients with a 10% to 24% increase in creatinine levels had a relative risk (RR) of death of 1.8 (95% confidence interval [CI], 1.3 to 2.5). By comparison, subjects with a 25% to 49% acute change in creatinine levels had an RR of death of 3.0 (95% CI, 1.6 to 5.8), and those with the largest change (≥50%) had the greatest RR of death (RR, 6.9; 95% CI, 2.0 to 24.5). Results were similar when absolute changes in creatinine levels were considered and when pooled estimates of adjusted RR were used.

Individual patient data were unavailable; thus, only group-level data were pooled for meta-analysis. Results showed a significant degree of statistical heterogeneity that was only partially ameliorated by separating studies into subsets based on clinical setting.

Short-term mortality and acute decreases in renal function are associated through a graded relationship such that even mild changes in serum creatinine levels portend worse outcome in a variety of clinical settings and patient-types.