What causes the cola-colored urine seen in rhabdomyolysis?

• A. Hemoglobin from red blood cell breakdown
• B. Myoglobin released from muscle tissue
• C. Bilirubin from liver disease
• D. Ketones from fat breakdown

Answer: (B)

Cola-colored urine in rhabdomyolysis comes from myoglobin released from damaged muscle tissue. When muscle cells break down, they spill myoglobin into the bloodstream. Myoglobin is a small, heme-containing protein, and as it is filtered by the kidneys its pigment can turn urine dark. At high levels, myoglobin can also injure renal tubules and contribute to acute kidney injury. This pigment specifically points to muscle breakdown, unlike bilirubin from liver disease or ketones from fat metabolism, which don’t cause the characteristic dark urine seen in rhabdomyolysis. Hemoglobin from red blood cell breakdown can darken urine in hemolysis, but in rhabdomyolysis the culprit is myoglobin released from muscle.