Enzymic assay for lecithin in amniotic fluid.

We describe an enzymic method for determining lecithin in amniotic fluid. Phospholipase D from savoy cabbage is used to liberate choline from lecithin, and the liberated choline is oxidized to betaine and hydrogen peroxide by choline oxidase from Arthrobacter globiformis. The hydrogen peroxide forms a colored complex with phenol and 4-aminoantipyrene in the presence of horseradish peroxidase, and this color is measured spectrophotometrically. The method is relatively easy, precise, and accurate, requires less time and sample than other methods, and offers a reliable alternative to the lecithin/sphingomyelin ratio techniques for assessing fetal lung maturity.