Prediction of respiratory distress syndrome using the Abbott FLM-II amniotic fluid assay

Most laboratories using the Abbott FLM-II assay for assessing fetal lung maturity follow the manufacturer's recommendations for interpreting the surfactant to albumin ratio (S/A). Thus, values >55 mg/g are considered mature and values <40 mg/g, immature-leaving a wide range of indeterminate values. Little data is available to assist the clinician in interpreting values between 40 and 55 mg/g. The goal of this study was to determine decision levels that would more clearly identify risk for RDS based on S/A results.

Respiratory distress syndrome was identified based on medical record review in 46 infants (born at six hospitals), who had S/A measurements on amniotic fluid within 72 h of delivery. An additional 257 women, who had had the S/A test requested but had non-RDS infants, were also identified for this study. The probability of RDS was calculated based on S/A values and on gestational age. Odds ratios were computed for different S/A ratios and different gestational ages.

Probability of RDS increased with decreasing S/A and decreasing gestational age. At gestational age >36 weeks, the probability of developing RDS ranged from 1% at S/A>44 mg/g to 39% at S/A44 mg/g to 92% at S/A

We report a risk-based approach for the clinical interpretation of the results of Abbott FLM-II assays based on a broad range of S/A values and gestational ages.