Comparison of the TDx-FLM II and lecithin to sphingomyelin ratio assays in predicting fetal lung maturity

Objective We evaluated the usefulness of the TDx-FLM II and lecithin to sphingomyelin (L/S) ratio assays in predicting fetal lung maturity. Study design We retrospectively reviewed 218 consecutive paired TDx-FLM II and L/S ratio results. Women who delivered viable infants within 72 hours of amniotic fluid collection (n = 109) were included in the analysis of sensitivity and specificity. Concordance between tests was determined for all women tested during the study period, and in the subset of women who delivered viable infants within 72 hours of amniotic fluid collection. Results There were 9 respiratory distress syndrome (RDS)-affected infants born during the study period. Both the TDx-FLM II and L/S ratios had 100% sensitivity in detecting RDS at their best apparent cut-offs. There was a trend towards increased specificity of the L/S ratio compared with the TDx-FLM II (80% for L/S vs 73% for FLM II). The overall concordance between the TDx-FLM II and L/S ratio was approximately 75%. Conclusion The TDx-FLM II and L/S ratios are both sensitive tests for RDS; however, there is not good concordance between the two. The results provide new insight into the optimal use, in sequential or reflex cascade testing, of the TDx-FLM II and L/S ratio.