Automated Rapid Assessment of Surfactant and Fetal Lung Maturity

Abstract

This study reports predictions for clinical respiratory distress syndrome (RDS) by means of a rapid test for fetal lung maturity based on fluorescence polarization of a dye (PCI 6) that partitions between surfactant and albumin in amniotic fluid. The test is completed in approximately 30 minutes and requires collection of a specimen volume of only 0.5 mL amniotic fluid. Results are reported as mg surfactantlg albumin (SIA value) equivalence. Ninety-three infants were delivered within 2 days of a collection of amniotic fluid and were followed up for the presence or absence of symptoms consistent with RDS. Ten infants, two of whom had anomalies, developed RDS. With a threshold of <50 mg/g equivalence to indicate probable occurrence of symptoms consistent with RDS, the SI A value had a sensitivity of 90% for predicting RDS, with a specificity of 87%, a positive predictive value of 45%, and a negative predictive value of 99%. This was comparable to using the lecithin-tosphingomyelin ratio of <2.0, which had a sensitivity of 80%, a specificity of 93%, and positive and negative predictive values of 57% and 98%, respectively. The clinical predictions based on the absence of phosphatidylglycerol were 90% sensitivity, 79% specificity, and 35% and 98% positive and negative predictive values, respectively. SI A values obtained for specimens that were frozen and thawed correlated well with results from nonfrozen specimens. Satisfactory S/A values were obtained with specimens of amniotic fluid that were collected from vaginal pools. Loss of fluorescence polarization because of partition of PCI 6 between albumin and surfactants represents an integrated effect of the surfactants and provides an additional assessment of lung maturity comparable to currently accepted tests. The ligand-based assay requires only a small volume of specimen, is rapid, and can be standardized between institutions. These features indicate that the PCI 6-based assay provides an alternative assessment of lung maturity to currently existing methodologies, or when little specimen is available or there is an urgent need for results.