DIAGNOSTIC PERFORMANCE OF A MATHEMATICAL FORMULA INTEGRATING SERUM AND BURN BULLA FLUID CREATININE FOR ACUTE KIDNEY INJURY IN SECOND-DEGREE (SUPERFICIAL, MID- AND DEEP-DERMAL) BURNS INVOLVING ≥25% TOTAL BODY SURFACE AREA AT DR. SAIFUL ANWAR GENERAL H

Background: Acute kidney injury (AKI) is a common complication of extensive burns associated with increased morbidity and mortality. Serum creatinine (SCr) has limited sensitivity for early AKI, and in second-degree burns creatinine may be lost into burn bullae. Objective: To evaluate a mathematical formula integrating SCr and burn bulla fluid creatinine (BCr) as a diagnostic parameter for AKI. Methods: Observational analytical cross-sectional study of patients with second-degree (superficial, mid- or deep-dermal) burns involving ≥25% total body surface area (TBSA) at Dr. Saiful Anwar General Hospital, East Java, Indonesia. SCr and BCr were measured enzymatically and combined, accounting for body weight, body surface area, burn extent and time since injury (42 × BW × SCr + 1.8 × BCr × t × TBSA × BSA). AKI was diagnosed by KDIGO 2012 criteria. Performance was assessed by receiver operating characteristic analysis, area under the curve (AUC), cut-off, sensitivity and specificity. Results: Thirty patients were included (20 male, 66.7%); AKI occurred in 13 (43.3%). Mean SCr and BCr were 1.18 ± 0.56 and 1.09 ± 0.54 mg/dL. The AUC was 0.910 (95% CI 0.801–1.000; p < 0.001). At ≥3,305.35, sensitivity was 84.6%, specificity 82.4%, positive predictive value 78.6% and negative predictive value 87.5%; the highest Youden index occurred at ≥3,178.81 (sensitivity 92.3%, specificity 82.4%). The serum term contributed over 99% of the mean formula value. Conclusion: The formula showed excellent discrimination for AKI in extensive second-degree burns, but its performance was driven predominantly by weight-scaled SCr. Correction of the serum-term scaling, assessment of the incremental value of BCr and external validation are required before clinical adoption.