A 22 year old man complains of leg pain after completing a cross fit class. He also notices darkening of his urine. You ask for a urine sample and he brings back the following.
What lab test should you order?
This patient’s story is concerning for rhabdomyolysis, which is hallmarked by muscle pain, weakness and dark coloured urine. It is important to recognize as muscle necrosis can lead to compartment syndrome, and myoglobin can be toxic to the renal tubular epithelium when found in high concentrations.
Other causes of rhabdomyolysis include trauma (e.g. crush or burn injuries), hyperthermia, metabolic myopathies (making muscle more prone to breaking down), and non-exertional etiologies (e.g. drugs like amphetamines, drugs causing prolonged immobility or infections).
It is important that you order a CK level, as it will be important to follow. Inpatient admission for hydration and monitoring should be considered in patients with significant symptoms limiting mobility, those with substance induced rhabdomyolysis, and those with signficiant CK elevations (e.g. > 5-10,000). Additionally, serum electrolytes (for hyperkalemia), extended electrolytes (patients trend towards hypocalcemia, hyperphosphatemia), creatinine and urea are important to trend. Metabolic acidosis is commonly seen.
Patients usually require aggressive volume recusistation with IV fluid at 150-200 ml/Hour until the CK is < 5000. However, as these patients are at risk of oliguric acute kidney injury, close attention should be paid to the urine output, including inserting a foley catheter if concerns arise. If there is concern about oliguria, nephrology should be involved early in the case management in case of the need for dialysis. Although dialysis can help with refractory volume over load, there is no evidence that you can remove myoglobin pigment or prevent damage to the kidneys by initiating early dialysis.