CK, Myoglobin and Rhabdomyolysis

Q: In rhabdomyolysis, which appears first in the plasma? (select one)

A) Creatine Kinase (CK)

B) Myoglobin 

Answer: B

The important lesson in rhabdomyolysis is independently reading CK and myoglobin in plasma and urine.

Myoglobin has a short half-life of couple of hours. In contrast, CK has a half-life of one and a half days. Myoglobin is quickly metabolized to bilirubin. Myoglobin appears in the plasma before CK elevation and returns to normal within six to eight hours. In contrast, CK may continue to rise in plasma. CK may remain elevated despite no myoglobinuria. 

Clinically, this is important as pigmenturia may be missing in rhabdomyolysis if a load of myoglobin is insufficient or resolved or the patient receives medical treatment early in the course. 

By conventional definition, rhabdomyolysis is five times or more above the upper limit of normal.

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References:

1. Giannoglou GD, Chatzizisis YS, Misirli G. The syndrome of rhabdomyolysis: Pathophysiology and diagnosis. Eur J Intern Med 2007; 18:90.

2. Gabow PA, Kaehny WD, Kelleher SP. The spectrum of rhabdomyolysis. Medicine (Baltimore) 1982; 61:141.