Creatine kinase isoenzymes in high-risk infants.

Serial measurements of serum creatine kinase isoenzymes were done from birth to 15 days of age in healthy premature infants, infants with perinatal or neonatal asphyxia and infants without asphyxia but with miscellaneous problems. Serum brain-specific fraction of creatine kinase (CK-BB) activity was higher in cord than in maternal serum (P < 0.01). In healthy infants, the serum activity of heart- and muscle-specific fractions of creatine kinase increased after birth, reached a plateau between 12 and 48 hr, and then declined, whereas the serum CK-BB decreased rapidly after birth and remained stable between 6 hr and 15 days. Compared to controls, infants with severe asphyxia and neurologic damage had a significant rise in serum CK-BB (P < 0.001). When the peak CK-BB level exceeded 35 IU/liter the mortality was high (83%). The increase in CK-BB was not observed in infants who received pentobarbital shortly after the episode of asphyxia. Diseases of the lung, kidneys, gastrointestinal tract, and abruptio placentae were not associated with increases of serum creatine kinase isoenzymes.