Exercise-Induced Rhabdomyolysis With Markedly Elevated Creatine Kinase and Preserved Renal Function

Exercise-induced rhabdomyolysis results from skeletal muscle injury after strenuous or unaccustomed exertion. Acute kidney injury is a feared complication, but creatine kinase magnitude alone is an imperfect predictor of kidney injury.

A 24-year-old previously healthy male presented with dark urine after one week of high-intensity resistance and eccentric exercise as a novice participant in structured high-intensity training. He reported daily oral hydration of more than 2.5 L and denied creatine monohydrate use. Initial tests showed creatine kinase of 79,038 U/L, creatinine of 1.3 mg/dL, estimated glomerular filtration rate of approximately 79 mL/min/1.73 m² by the 2021 CKD-EPI creatinine equation, aspartate aminotransferase (AST) of 507 U/L, and urine dipstick blood of 3+ with few red blood cells. Urea, potassium, calcium, magnesium, and phosphorus were within reference ranges, and urinalysis showed only trace protein without leukocytes or nitrites. He received isotonic intravenous fluids without bicarbonate, diuretics, or renal replacement therapy. Creatinine decreased to 0.6 mg/dL within 24 h and remained stable; urine dipstick blood became negative by Day 2; creatine kinase declined to 722 U/L by Day 10 and 287 U/L by Day 16, while creatinine remained normal at 0.7 mg/dL and aminotransferases improved to AST of 25 U/L and ALT of 42 U/L.

This case is best interpreted as severe exertional rhabdomyolysis with pigmenturia and preserved renal function, rather than confirmed intrinsic acute kidney injury. The report highlights the need to avoid creatine kinase-centric risk assessment and to interpret a mildly elevated admission creatinine in context, especially when rapid normalization follows fluid resuscitation.