From the Guidelines
Rhabdomyolysis is best diagnosed through a combination of clinical assessment, laboratory tests, and patient history, with a focus on measuring creatine kinase (CK) levels, myoglobin, and plasma creatine phosphokinase (CPK) in the blood, as well as monitoring urine output and pH. The diagnosis of rhabdomyolysis involves a range of laboratory tests and clinical assessments, including:
- Measuring creatine kinase (CK) levels in the blood, with values typically exceeding 1,000 U/L and often reaching tens of thousands or even hundreds of thousands in severe cases 1
- Elevated myoglobin in blood and urine, which can be an earlier and more sensitive indicator of acute kidney injury than CK levels 1
- Hyperkalemia, elevated creatinine, elevated liver enzymes (AST, ALT), and metabolic acidosis 1
- Urinalysis showing dark, tea-colored urine and testing positive for blood on dipstick without red blood cells under microscopy (due to myoglobinuria)
- Clinical presentation including muscle pain, weakness, and swelling, though symptoms can range from mild to severe
- A thorough history to identify potential causes such as trauma, extreme exercise, medications (particularly statins), illicit drugs, infections, or metabolic disorders A repeated bio-assessment combining plasma myoglobin, plasma creatine phosphokinase (CPK) and kalaemia measurements, as well as bladder catheterisation to monitor hourly urine output and urine pH, is probably recommended to detect acute kidney injury in patients suffering from post-traumatic acute rhabdomyolysis 1. Early diagnosis is crucial as rhabdomyolysis can lead to acute kidney injury, electrolyte abnormalities, and compartment syndrome, and treatment should be initiated promptly to prevent complications.
From the Research
Diagnosis of Rhabdomyolysis
The diagnosis of rhabdomyolysis is primarily based on the following criteria:
- Elevated creatine kinase (CK) levels, with many clinicians using five times the upper limit of normal (approximately 1000 U/l) as a cut-off point 2
- Presence of myoglobinuria, which can cause tea-colored urine 3
- Electrolyte abnormalities, such as hyperkalemia 4, 2
- Acute kidney injury (AKI), which can occur in 4%-33% of patients 2
Laboratory Findings
Laboratory findings that support the diagnosis of rhabdomyolysis include:
- Elevated plasma creatine kinase level, which is the most sensitive laboratory finding of muscle injury 3
- Elevated serum creatine phosphokinase (CPK) levels 2
- Myoglobinuria, which can be detected in the urine 4, 3
- Electrolyte imbalances, such as hyperkalemia 4, 2
Electromyography (EMG) Findings
EMG findings in acute rhabdomyolysis are often normal, but when abnormal, the changes are subtle and may include:
- Variable proximal myopathic motor unit action potentials 5
- Myopathic EMG changes in 1 to 3 sampled proximal muscles 5
- No persistent fibrillation potentials 5
Additional Testing
Additional testing may be necessary to evaluate for potential causes of rhabdomyolysis, such as: