Effect of differences in saturation sensitivity of phospholipid stains on clinical predictivity of L/S ratios

Owing to the importance of the degree of fatty acid side chain saturation in the ability of lecithin molecules to function as surfactant, we assessed the clinical effectiveness of analytical methods which differ with respect to methodologic influences by saturated and unsaturated phospholipids. The lecithin/sphingomyelin ratios, determined with either cupric acetate or phosphomolybdate as the detection reagent, are compared for their abilities to predict respiratory distress syndrome (RDS), transient tachypnea (TTN), or the absence of respiratory difficulty in neonates. A group of 47 amniotic fluids were analyzed from 25 non-problem cases, 13 cases of TTN and 9 cases of RDS. Receiver operating characteristic analysis shows that in our sample population, the measurement of total lecithin for the prediction of neonatal respiratory distress failed to demonstrate an advantage over the measurement of unsaturated lecithin alone.