From the Guidelines
The primary test for diagnosing rhabdomyolysis is measuring serum creatine kinase (CK) levels in the blood, with a significantly elevated CK level, typically at least 5 times the upper limit of normal (often >1,000 U/L), being the most sensitive indicator of muscle breakdown. This is based on the most recent evidence from 2021, which suggests that raising CPK levels above five times normal is a sign of rhabdomyolysis 1. When muscle cells are damaged, they release CK into the bloodstream, making it an excellent marker for rhabdomyolysis.
Some key points to consider when diagnosing rhabdomyolysis include:
- Measuring plasma myoglobin, which has an earlier peak plasma concentration than CPKs, may be more sensitive and specific than CPKs in identifying the risk of acute kidney injury, which is correlated with increased mortality 1
- Checking for myoglobinuria (myoglobin in urine), which often causes tea or cola-colored urine
- Measuring other muscle enzymes like aldolase, lactate dehydrogenase (LDH), and aminotransferases (AST/ALT)
- Electrolyte abnormalities such as hyperkalemia, hyperphosphatemia, hypocalcemia, and elevated blood urea nitrogen (BUN) and creatinine may also be present, particularly if kidney injury has occurred
- Urinalysis using a dipstick may be positive for blood without red blood cells visible under microscopy, as the test detects myoglobin
It is also recommended to perform 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, which should be maintained at 6.5 1. Early diagnosis is crucial as prompt treatment with aggressive intravenous fluid administration can prevent acute kidney injury, the most serious complication of rhabdomyolysis.
From the Research
Diagnosis of Rhabdomyolysis
The primary test for diagnosing rhabdomyolysis involves:
- Elevated creatine kinase (CK) levels, which is a key indicator of muscle damage 2, 3, 4, 5
- Urine myoglobin levels, which are also markedly elevated in rhabdomyolysis 4, 6
- Clinical examination, history, laboratory studies, muscle biopsy, and genetic testing can also be useful tools for diagnosis 4
Laboratory Tests
Laboratory tests used to diagnose rhabdomyolysis include:
- Serum creatine kinase levels, which are markedly elevated in rhabdomyolysis 2, 3, 4, 5
- Urine myoglobin levels, which can indicate the presence of rhabdomyolysis 4, 6
- Electrolyte abnormalities, such as hyperkalemia, which can be a complication of rhabdomyolysis 2
Diagnostic Criteria
A systematic review recommends a clinical syndrome of acute muscle weakness, myalgia, and muscle swelling combined with a CK cut-off value of > 1000 IU/L or CK > 5 × upper limit of normal (ULN) for the standard definition of a mild rhabdomyolysis 5
- Measured myoglobinuria and acute kidney injury (AKI) can indicate a severe type of rhabdomyolysis 5