Detection of phosphatidylglycerol in frozen amniotic fluid by rapid assay of fetal lung maturity.

Objective: The study objective was to analyze the accuracy of the antibody-mediated rapid assay slide agglutination AmnioStat-FLM (Irvine Scientific, Santa Ana, CA) test in detecting the presence or absence of phosphatidylglycerol (PG) in amniotic fluid samples that have been frozen.

Study Design: A prospective blinded evaluation was performed in which fresh samples of amniotic fluid were initially analyzed for PG by the rapid assay (AmnioStat-FLM) test and the results reported for patient management. The specimens were then coded, patient identification was removed and specimens were then frozen. The samples were then thawed and the AmnioStat-FLM test was performed a second time with the laboratory technicians blinded to the original test result. Neonatal outcome and the source of the sample, including the presence of blood and meconium, were recorded.

Results: A total of 200 specimens were evaluated with 197 (98.5%) concordant between the initial test result and the result after the freeze-thaw process regarding the reporting results of either the presence or absence of PG (95% CI 94-99%). The result also was not affected by the source of the specimen or the presence of blood or meconium.

Conclusion: Freezing and thawing of amniotic fluid had minimal affect on the antibody-mediated rapid assay slide agglutination (AmnioStat-FLM) test result.