Summary
Serial quantitative immunoelectrophoretic (IE) measurements of antithrombin III heparin
cofactor (AT III) were made in groups of well and sick newborn infants classified
by gestational age. Collection methods (venous vs. capillary) did not influence the
results; serum IE measurements were comparable to AT III activity by a clotting method.
AT III is gestational age-dependent, increasing from 28.7% of normal adult values
at 28-32 weeks to 50.9% at 37-40 weeks, and shows a gradual increase to term infant
levels (57.4%) by 3-4 weeks of age. Infants with the respiratory distress syndrome
(RDS) show lower levels of AT III in the 33-36 week group, 22% vs. 44% and in the
37-40 week group, 33.6% vs. 50.9%, than prematures without RDS. Infants of 28-32 week
gestational age had only slight differences, RDS = 24%, non-RDS = 28.7%. The lowest
levels of AT III were seen in patients with RDS complicated by disseminated intravascular
coagulation and those with necrotizing enterocolitis. Crossed IE on representative
infants displayed a consistent pattern which was identical to adult controls except
for appropriate decreases in the amplitude of the peaks. The thrombotic complications
seen in the sick preterm infant may be related to the low levels of AT III.
