Exertional rhabdomyolysis: clinical features, management, complications and prediction of acute kidney injury.

Objectives: To describe the clinical course and complications of exertional rhabdomyolysis, compare inpatient and outpatient management, and evaluate admission markers of acute kidney injury (AKI). Methods: Prospective, multicentre study with consecutive inclusion of patients with rhabdomyolysis (creatine kinase (CK) ≥5000 U/L and/or myoglobin ≥1000 ng/mL) with exercise as the precipitating factor, presenting to the emergency departments of four hospitals in Oslo and Akershus, Norway (2019-2022). Management followed usual care. Primary outcome was AKI, defined by Kidney Disease: Improving Global Outcomes criteria. Results: We included 136 patients with exertional rhabdomyolysis (median age 28 years, 55% male), mainly after strength training (106, 78%); 62 (46%) were managed as inpatients and 74 (54%) as outpatients. Management was similar in both groups, consisting of fluids, serial blood tests, with a median follow-up of 3 days. Complications were rare and no outpatients required escalation to inpatient care. Five (4%) patients developed AKI (median peak creatinine 217 µmol/L, 132-410). Other major complications (severe electrolyte disturbances and compartment syndrome) occurred only in those with AKI.All patients who developed AKI had serum creatinine above the normal reference range at admission, though a few patients with elevated creatinine did not develop AKI (95% specificity). The myoglobin-to-CK ratio (≥0.48) performed best among muscle injury biomarkers and might serve as a supportive high-risk marker (99% specificity). Conclusion: No patient with a normal admission creatinine developed AKI in this cohort, supporting outpatient management as a safe option for otherwise healthy individuals when admission creatinine is within the reference range, provided follow-up is ensured. Trial registration number: NCT04118608.