ANALYTICAL AND CLINICAL-EVALUATION OF REFRACTIVE INDEX-MATCHED ANOMALOUS DIFFRACTION (RIMAD) FOR ASSESSMENT OF FETAL LUNG MATURATION

We have evaluated refractive index-matched anomalous defraction (RIMAD ) (Dubin SB, Clin Chem 1988;34:938-43) as a potential method for asses sment of fetal lung maturity (FLM). This method determines the total l ight scattered by the surfactant-containing lamellar bodies by subtrac tion of the A(650) from amniotic fluid diluted in glycerol from that o f amniotic fluid diluted in distilled water. It is not significantly a ffected by such contaminating chromogens as hemoglobin and bilirubin u p to 2.0 g/L and 11.0 mg/L, respectively. However, the addition of as little as 2.5 mu L of erythrocytes as whole blood resulted in signific ant interference. RIMADs for normal respiratory outcomes (n = 78) rang ed from 0.018 to 0.471, RIMADs for respiratory distress syndrome (RDS) outcomes (n = 8) ranged from 0.004 to 0.036. Use of a RIMAD referent value of >0.040 to indicate maturity yielded sensitivity, specificity, predictive value (PV)(RDS), and PVmaturity of 100%, 96.2%, 72.2%, and 100%, respectively. The areas under the receiver-operating characteri stic curves were 0.997 for the RIMAD assay, 0.993 (P = 0.3) for the TD x-FLM assay, 0.89 (P = 0.017) for the lecithin/sphingomyelin ratio, an d 0.87 (P = 0.023) for the foam stability index.