A 24-year-old man presents to the emergency department with severe, bilateral thigh and shoulder pain, along with dark-colored urine. He reports that he participated in his first high-intensity interval training session earlier today. His temperature is 37.1°C (98.8°F), blood pressure is 120/80 mmHg, and pulse is 95/min. Physical examination shows diffusely tender and mildly swollen quadriceps and deltoid muscles. Which of the following is the most appropriate next step in laboratory evaluation?
- AMagnetic resonance imaging of the affected muscles
- Serum creatine kinase levelAnswer
- CPercutaneous muscle biopsy
- DUrine myoglobin assay
- EErythrocyte sedimentation rate
Answer
Serum creatine kinase level
The correct answer is the serum creatine kinase level. This patient's presentation of severe muscle pain and dark urine following intense exercise is highly characteristic of exertional rhabdomyolysis. The dark urine is typically due to myoglobinuria. The most appropriate initial laboratory test to confirm the diagnosis of rhabdomyolysis is a serum creatine kinase (CK) level. CK is an enzyme found in high concentrations in skeletal muscle, and its release into the blood is a highly sensitive and reliable marker of muscle necrosis. A CK level greater than 5 times the upper limit of normal (or typically >1,000 U/L) in the appropriate clinical setting confirms the diagnosis.
Step-by-Step Solution
Key Concept
The initial laboratory evaluation of suspected rhabdomyolysis should prioritize measuring the serum creatine kinase level, which is the most sensitive indicator of muscle injury.
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