Improved fluorescence polarization assay for use in evaluating fetal lung maturity. I. Development of the assay procedure.

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We describe a fluorescence polarization assay for use in predicting fetal lung maturity, which is suitable for the TDx Analyzer (an automated fluorescence polarimeter). The assay requires 0.5 mL of amniotic fluid and approximately 30 min, and involves the fluorophore 1-palmitoyl-2(6-[(7-nitro-2, 1, 3-benzoxadiazol-4-yl)amino]caproyl) phosphatidylcholine. Reproducible polarization measurements depend on proper regulation of incubation time and temperature, but variations in the concentrations of fluorescent probe and amniotic fluid have little effect on measured polarization and therefore little effect on assay precision. Working solutions of the fluorescent probe are stable for at least nine months when stored at -20 degrees C and pH 5. Interferences include erythrocytes, serum, bilirubin, meconium, and lidocaine.