To the Editor.—
The report by Siegel et al on elevations of serum CK-MB isoenzyme levels in marathon runners contains several inaccuracies. The MB level is alleged to correlate "with the serum myoglobin level as a sensitive biochemical marker for the extent of exertional rhabdomyolysis." In the reference cited for this correlation CK isoenzymes were not measured.1 The correlation was between total CK levels and rhabdomyolysis. It is further asserted that mild abnormalities of CK-MB can be seen after recreational exercise of unselected volunteers. Again the authors in the reference cited to support this contention evaluated only total CK and did not measure isoenzymes.2 Kaman et al,3 using electrophoresis, could not detect elevations of CK-MB in the blood of joggers after near-maximum exercise.Dr Siegel and associates state that "unlike enzymes widely distributed in human tissues, creatine kinase is found only in muscle cells." Skeletal muscle and
Warkel RL. Elevated CK-MB Levels in Marathon Runners. JAMA. 1982;247(17):2368. doi:10.1001/jama.1982.03320420024013
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