RAPID FETAL LUNG MATURITY TESTING: COMMERCIAL VERSUS NBD-PHOSPHATIDYLCHOLINE ASSAY

We compared the TDx Fetal Lung Maturity test and the fluorescence polarization method using l-palmitoyl-2{6-[(7- nitro-2,l,3-benzoxadiazol-4-yl)amino]caproyl}phosphatidylcholine (NBD-phosphatidylcholine). Using 76 paired human amniotic fluid samples, the fluorescence polarization values of the two methods were found to have a strong nonlinear correlation (r2=0.946). Both assays can be completed in less than 1 hour, have excellent precision (between- day variation less than 2%), and indicate the amount of surfactant phospholipid relative to albumin. The FLM assay is calibrated with surfactant/albumin standards; therefore, the reported results (in mg/g) correlate inversely with polarization of NBD-phosphatidylcholine. Strong correlations were seen for both assays with the lecithinsphingomyelin ratio and phosphatidylglycerol. The correlations indicate that the recommended reference range for FLM will have more false predictions of immaturity than the NBD-phosphatidylcholine assay. (Obstet Gynecol 1992;801048-53)