Low protein C in the neonatal period.

Protein C was measured by electroimmunoassay in 47 infants within 24 h of delivery. Gestational age ranged from 28 to 43 weeks. The mean level was 27% (range less than 10-67%) of the normal adult mean. In the 22 infants who had no clinical problems, protein C levels correlated significantly with gestational age. In the 25 who were sick there was no correlation, and the mean level was significantly lower than that of the healthy infants. Postnatal rise was slow; on day 7 the mean was 32% and on day 28, 31%. Levels of protein C correlated significantly with prothrombin in both the healthy and sick infants. Crossed immunoelectrophoresis in the presence of calcium ions gave one protein C peak of the same electrophoretic mobility as is seen in plasma of healthy adults, indicating that the infants' protein C is gamma carboxylated. It is concluded that: (1) Protein C in neonates is in or below the range associated with thromboembolism in patients congenitally deficient in this protein; (2) protein C levels correlate with gestational age; and (3) the low levels during the neonatal period are not due to decreased gamma carboxylation but may reflect decreased synthesis when compared to the older child or the adult.