Serum cystatin C- versus creatinine-based definitions of acute kidney injury following cardiac surgery: a prospective cohort study.

BACKGROUND

The primary aim of this study was to compare the sensitivity and rapidity of acute kidney injury (AKI) detection by cystatin C level relative to creatinine level after cardiac surgery.

STUDY DESIGN

Prospective cohort study.

SETTINGS & PARTICIPANTS: 1,150 high-risk adult cardiac surgery patients in the TRIBE-AKI (Translational Research Investigating Biomarker Endpoints for Acute Kidney Injury) Consortium.

PREDICTOR

Changes in serum creatinine and cystatin C levels.

OUTCOME

Postsurgical incidence of AKI.

MEASUREMENTS

Serum creatinine and cystatin C were measured at the preoperative visit and daily on postoperative days 1-5. To allow comparisons between changes in creatinine and cystatin C levels, AKI end points were defined by the relative increases in each marker from baseline (25%, 50%, and 100%) and the incidence of AKI was compared based on each marker. Secondary aims were to compare clinical outcomes among patients defined as having AKI by cystatin C and/or creatinine levels.

RESULTS

Overall, serum creatinine level detected more cases of AKI than cystatin C level: 35% developed a ≥25% increase in serum creatinine level, whereas only 23% had a ≥25% increase in cystatin C level (P < 0.001). Creatinine level also had higher proportions meeting the 50% (14% and 8%; P < 0.001) and 100% (4% and 2%; P = 0.005) thresholds for AKI diagnosis. Clinical outcomes generally were not statistically different for AKI cases detected by creatinine or cystatin C level. However, for each AKI threshold, patients with AKI confirmed by both markers had a significantly higher risk of the combined mortality/dialysis outcome compared with patients with AKI detected by creatinine level alone (P = 0.002).

LIMITATIONS

There were few adverse clinical outcomes, limiting our ability to detect differences in outcomes between subgroups of patients based on their definitions of AKI.

CONCLUSIONS

In this large multicenter study, we found that cystatin C level was less sensitive for AKI detection than creatinine level. However, confirmation by cystatin C level appeared to identify a subset of patients with AKI with a substantially higher risk of adverse outcomes.