Antithrombin III levels in term and preterm infants measured by rate nephelometry

The plasma antithrombin III level was measured in term and premature newborns within the first 24 h of life; in addition to the authors', own immunological method utilizing rate nephelometry the assays of Laurell and Kabi Coatest were used. Antithrombin III concentration showed a linear correlation with the degree of maturity, in accordance with previous data. The lowest values were found in premature babies affected by idiopathic respiratory distress syndrome who later developed pulmonary haemorrhage. At all gestational ages the antithrombin III functional index was lower than 1.0, indicating antithrombin III consumption. Since both concentration and activity of antithrombin III are low in prematures, they are at an increased risk for coagulopathies, hence substitution therapy is indicated. Measurement of antithrombin III by rate nephelometry can also be used for following changes in inhibitor concentration.