Fluid balance -adjusted creatinine in diagnosing Acute Kidney Injury in the critically ill.

Abstract

BACKGROUND: Acute Kidney Injury (AKI) is often diagnosed based on plasma creatinine (Cr) only. Adjustment of Cr for cumulative fluid balance due to potential dilution of Cr and subsequently missed Cr-based diagnosis of AKI has been suggested, albeit the physiological rationale for these adjustments is questionable. Furthermore, whether these adjustments lead to a different incidence of AKI when used in conjunction with urine output criteria is unknown. METHODS: This was a post-hoc analysis of the Finnish Acute Kidney Injury study. Hourly urine output and daily plasma Cr were measured during the first five days of ICU admission. Cr values were adjusted following the previously used formula and combined with the urine output criteria. Resulting incidences and mortality rates were compared with the results based on unadjusted values. RESULTS: In total, 2044 critically ill patients were analyzed. The mean difference between the adjusted and unadjusted Cr of all 7279 observations was 5 (±15) micromol/L. Using adjusted Cr in combination with urine output and RRT criteria resulted in the diagnosis of 19 (1%) additional AKI patients. The absolute difference in the incidence was 0.9% (95% CI; 0.3 -1.6%). Mortality rates were not significantly different between the reclassified AKI patients using the full set of KDIGO criteria. CONCLUSION: Fluid balance -adjusted Cr resulted in little change in AKI incidence, and only minor differences in mortality between patients who changed category after adjustment and those who did not. Using adjusted Cr values to diagnose AKI does not seem worthwhile in critically ill patients.