Serum creatine phosphokinase in normal newborns.

Serum creatine phosphokinase (CPK) activity in 70 normal newborns was found to be significantly higher than the normal values found in adults or older children, and in some cases reached a level up to 10 times normal. It declined to near normal activity during the first 4 days and to normal level of activity by age 6-10 weeks. No clear correlation between birth trauma and increase in serum CPK activity was shown. CPK activity in cord blood was lower than in venous and capillary blood. Because of the increased CPK activity found in normal newborns, screening for Duchenne-type muscular dystrophy should be postponed for a few weeks after delivery.