An increased incidence of augmented renal clearance (ARC) has been reported in traumatic brain injury (TBI) patients. Because ARC can cause transient disruptions in electrolytes and serum drug concentrations, detection of ARC is crucial. This study aimed to investigate the detection of ARC in TBI patients by using two different evaluations of Modification of Diet in Renal Disease (MDRD) Estimated Glomerular Filtration Rate (eGFR) and the Cockcroft-Gault equation.

This single-center retrospective cohort study evaluated patients diagnosed with TBI on admission between January 2017 and August 2025. TBI severity was classified according to the Glasgow Coma Scale score at admission as mild (GCS 13–15), moderate (GCS 9–12), or severe (GCS 3–8). Patients with a premorbid diagnosis of chronic kidney disease were excluded. ARC was defined as a renal clearance >130 mL/min utilizing either of two distinct equations: 1) the MDRD modified for Japanese population or 2) creatinine clearance (CrCl) calculated by the Cockcroft-Gault equation. Participants were followed up until discharge or day 21 of their hospital stay.

A total of 140 patients were included, of whom 58 (41.4%) developed ARC during the observation period. Among patients with ARC, 24 (41.4%) were detected by both the MDRD and Cockcroft–Gault equations, whereas 12 (20.7%) were detected only by the MDRD equation and 22 (37.9%) only by the Cockcroft–Gault equation. Patients with MDRD-only ARC were older and had significantly lower BMI than Cockcroft–Gault-detected ARC patients. Detection of ARC in MDRD-only patients was significantly later. The incidence of ARC increased with TBI severity (30.5% in mild, 44.4% in moderate, and 62.5% in severe TBI), however TBI severity was not significantly different between the MDRD-only and the other groups.

Later detection of ARC only by MDRD may indicate loss of muscle and subsequent reduction of creatinine production. This may suggest overdiagnosis of ARC by using MDRD formula.