Myoglobin-to-creatine kinase ratio enhances prediction of acute kidney injury in rhabdomyolysis

BACKGROUND: Acute kidney injury (AKI) is a key complication of rhabdomyolysis. Creatine kinase (CK), the standard muscle injury biomarker, has limited predictive value. Myoglobin may be more accurate but has its limitations. The myoglobin-to-CK ratio may be a stronger predictor but lacks prospective validation. We aimed to validate this ratio using admission values, compare it with CK and myoglobin, and identify thresholds for early AKI risk stratification. METHODS: Prospective multicentre cohort study across four hospitals in Oslo and Akershus, Norway (2019-2022). All adults with CK ≥5000 U/L and/or myoglobin ≥1000 ng/mL at emergency department presentation or within 72 hours thereafter were eligible, irrespective of admission. Primary outcome was AKI. Predictive performance of CK, myoglobin and the myoglobin-to-CK ratio was assessed using logistic regression and receiver operating characteristic (ROC) analysis. RESULTS: In the 310 included patients, 108 (35%) developed AKI. In ROC analysis the myoglobin-to-CK ratio was the strongest predictor of AKI on admission (area under the curve (AUC) 0.84, 95% CI 0.79 to 0.89), followed by myoglobin (AUC 0.73, 95% CI 0.67 to 0.79); CK was a weak predictor (AUC 0.31, 95% CI 0.25 to 0.37). In quartile analysis, 72% of patients in the highest ratio quartile developed AKI, with a ratio ≥0.20 indicating risk. For myoglobin, 65% in the highest quartile developed AKI, with values ≥6372 ng/mL indicating risk. ROC analysis identified optimised cut-offs of 0.48 for the ratio (sensitivity/specificity 79/82%) and 4489 ng/mL for myoglobin (61/76%). Combined, these cut-offs increased sensitivity and negative predictive value to 89% (95% CI 81.3% to 94.4%) and 92% (95% CI 86.2% to 96.0%), respectively, suggesting potential for identification of both high-risk and low-risk patients at admission. CONCLUSIONS: The myoglobin-to-CK ratio was the strongest early predictor of AKI. Combined with myoglobin ≥4489 ng/mL, a ratio ≥0.48 identified 89% of AKI cases and ruled out 92% of non-AKI cases, suggesting a potential admission-based tool for early AKI risk stratification in rhabdomyolysis. TRIAL REGISTRATION NUMBER: NCT04118608.