Hyperfiltration in Critically Ill Older Adults: Incidence, Risk Factors, Time Course, and Predictive Performance of Kidney Function Estimation

STUDY OBJECTIVE: This study aimed to evaluate the incidence, associated risk factors, time course, and predictive performance of kidney function estimation equations for hyperfiltration in critically ill older adults. METHODS: This retrospective observational study evaluated 325 patients (median age, 76 years) admitted to the intensive care unit (ICU) of a tertiary-care university hospital, for a total of 2934 patient-days. The hyperfiltration threshold was defined using measured creatinine clearance (Clcr) > -0.883 × age + 167.398. Independent factors associated with hyperfiltration were identified via a multivariable logistic regression model, and time to onset and duration were evaluated using Kaplan-Meier curves. Additionally, the predictive performance of the measured Clcr was assessed using the Cockcroft-Gault equation. Bias was analyzed using the Bland-Altman analysis, and accuracy was evaluated using the percentage within 30% of the measured Clcr (P30). RESULTS: Hyperfiltration occurred in 56% of the patients. Risk factors included male sex, high body mass index, trauma-related admission, vasopressor use, and low serum creatinine levels. The median time from ICU admission to hyperfiltration onset was 5 days, and the median duration of hyperfiltration episodes was 8 days. The Cockcroft-Gault equation substantially underestimated measured Clcr in patients with hyperfiltration. Even among those whose measured Clcr did not meet the conventional augmented renal clearance (ARC) threshold (> 130 mL/min), the equation exhibited a clinically significant negative bias (-35 mL/min) with limited accuracy (P30: 39%). This underestimation was even more pronounced in patients meeting the ARC criteria (bias: -62 mL/min; P30: 27%). CONCLUSIONS: Hyperfiltration is highly prevalent in critically ill older adults. The Cockcroft-Gault equation substantially underestimated actual kidney function, even without meeting the ARC criteria. Continuous monitoring of the measured Clcr is recommended to avoid inappropriate medication dose reductions due to underestimation.