A new method for measurement of surfactant specific apoprotein in amniotic fluid.

A simple and rapid method for the quantitative measurement of surfactant specific apoprotein concentration in amniotic fluid was developed using the measurement of immunological reactions by the nephelometric technique. Use of this method made it possible to measure 0.5-8.0 micrograms apoproteins per ml within approximately 70 min. Surfactant specific apoproteins in 54 samples of amniotic fluid were measured using the method. The surfactant specific apoprotein concentration in amniotic fluid increased from 1.03 +/- 0.51 micrograms/ml (mean +/- S.D.) at 26-30 weeks of gestation to 4.45 +/- 2.08 micrograms/ml at 36 weeks of gestation or more. Among premature infants, who were delivered within 24 h afer amniocentesis, surfactant specific apoprotein concentration was less than 1.5 micrograms/ml in three infants with respiratory distress syndrome (RDS), and more than 2.1 micrograms/ml in six without RDS. The results indicated that the quantitative measurement of surfactant specific apoprotein in amniotic fluid is effective in predicting the fetal lung maturity, and that simplicity and rapidity make our method useful for clinical application.