What are the key clinical features and laboratory findings that suggest a diagnosis of rhabdomyolysis in a primary care setting?

In a primary care setting, the diagnosis of rhabdomyolysis is suggested by a combination of key clinical features and specific laboratory findings NICE CKS,NICE NG148.

Clinical Features:

• Patients often present with muscle pain (myalgia), which can be severe, and muscle weakness Cervellin et al. 2010Szumilak et al. 1998.
• A classic, though not universally present, sign is dark, reddish-brown urine, resulting from myoglobinuria Cervellin et al. 2010.
• Other non-specific symptoms may include general malaise, fatigue, nausea, vomiting, and abdominal pain Szumilak et al. 1998.

Laboratory Findings:

• The most indicative laboratory finding is a significantly elevated Creatine Kinase (CK) level, often exceeding five times the upper limit of normal, or greater than 1000 U/L, though levels can be much higher Cervellin et al. 2017.
• Myoglobinuria, detected by a positive dipstick test for blood in the absence of red blood cells on microscopy, confirms the presence of myoglobin in the urine Cervellin et al. 2017.
• Electrolyte abnormalities are common due to muscle cell breakdown, including hyperkalaemia, hyperphosphataemia, and early hypocalcaemia Cervellin et al. 2017. Hypercalcaemia may occur later during the recovery phase Cervellin et al. 2017.
• Evidence of acute kidney injury (AKI) is a significant concern and may be indicated by elevated serum creatinine and urea, and a reduced glomerular filtration rate (GFR) NICE CKS,NICE NG148 Cervellin et al. 2017.
• Metabolic acidosis may also be present Cervellin et al. 2017.