Which lab finding would strongly lead you to the diagnosis of rhabdomyolysis?

Which lab finding would strongly lead you to the diagnosis of rhabdomyolysis?

• A. Elevated CK
• B. Hyperkalemia
• C. Elevated AST
• D. Blood on urine dipstick with negative microscopic exam

Answer: (D)

The strongest clue for rhabdomyolysis is a urinalysis pattern where the dipstick is positive for blood, but microscopic examination shows few or no red blood cells. This happens because damaged muscle releases myoglobin into the bloodstream and then into the urine. The dipstick detects heme and will turn positive for both blood and myoglobin, but since the urine contains myoglobin rather than intact red blood cells, the microscopy doesn’t show many RBCs. Other abnormalities can occur with muscle injury, like elevated creatine kinase, which is common but not as specific to the urine clue, or elevations in AST and potassium, which can occur in various conditions and are not as diagnostic by themselves. The urine finding described is the classic, more specific hint pointing directly toward myoglobinuria from rhabdomyolysis.

The strongest clue for rhabdomyolysis is a urinalysis pattern where the dipstick is positive for blood, but microscopic examination shows few or no red blood cells. This happens because damaged muscle releases myoglobin into the bloodstream and then into the urine. The dipstick detects heme and will turn positive for both blood and myoglobin, but since the urine contains myoglobin rather than intact red blood cells, the microscopy doesn’t show many RBCs.

Other abnormalities can occur with muscle injury, like elevated creatine kinase, which is common but not as specific to the urine clue, or elevations in AST and potassium, which can occur in various conditions and are not as diagnostic by themselves. The urine finding described is the classic, more specific hint pointing directly toward myoglobinuria from rhabdomyolysis.