[Assessment of fetal lung maturity by immunological measurement of fetal pulmonary surfactant apoproteins in amniotic fluid (author's transl)].

The pulmonary surfactant consists of phospholipid and 10% apoprotein. The lipid fraction has been extensively studied. The protein fraction, however has not been completely dissolved. We isolated the surfactant from autopsy human lung washing fluid and amniotic fluid. By SDS-polyacrylamide gel electrophoresis, the molecular weights of the two surfactant apoproteins were estimated to be approximately 36,000 and 16,000. The identity of surfactant fractions from both lung washing and amniotic fluid was demonstrated by immunodiffusion and immunoelectrophoresis. The pulmonary surfactant apoproteins in amniotic fluid was measured by using Laurell rocket immunoelectrophoresis. The pulmonary surfactant became detected from 32 week gestation in amniotic fluid, and its concentration increased significantly at 36 week gestation. The coefficient of correlation between surfactant apoprotein and shake test was 0.76, and that of between apoprotein and disaturated lecithin (DSL) was 0.61. Amniotic fluid contaminated with blood or meconium are often false positive results in shake test or DSL concentration. On the other hand, the apoprotein determination by Laurell's method, which however was too complicated to perform clinically, gave reliability regardless of the contamination.