An examination of some factors influencing creatine kinase in the blood of patients with muscular dystrophy.

The natural variability of plasma creatine kinase activity has been examined in patients suffering from muscular dystrophy and in normal subjects. The coefficient of variation of the plasma creatine kinase activities was found to be large (approximately 35%) in both patients with Duchenne muscular dystrophy and normal control subjects. A comparison of the plasma activities of creatine kinase with other muscle-derived enzymes suggests that the cause of this variability is changes in the release of enzymes from muscle. Data obtained concerning the effect of physical activity on plasma creatine kinase activity are contradictory, but several young patients with Duchenne muscular dystrophy and a very high creatine kinase activity (greater than 5000 IU/liter) showed a decreased activity following admission to hospital. An estimate of the rate of efflux of certain kinase from muscle has been made, indicating that young ambulant patients with Duchenne muscular dystrophy have a grossly elevated muscle creatine kinase efflux (495.0 +/- 61.3 IU/kg muscle/hr) compared to control subjects (1.4 +/- 0.5 IU/kg muscle/hr).