A new method of evaluating fetal lung maturity: the enzymatic lecithin determination in amniotic fluid.

The concentration of phospholipids is well suited as indicator for the prognosis of a possibly postnatal respiratory distress syndrome. The method used most frequently up to now has been the determination of the lecithin/sphingomyelin ratio (L/S ratio) by thin layer chromatography. We have developed a specific assay for the quantitative determination of lecithin in amniotic fluid, which yields absolute concentration values and does not require the determination of a concentration ratio. Lecithin is hydrolized by phospholipase C and alkaline phosphatase. Choline is determined afterwards by a highly specific choline kinase from yeast. The total time required is less than 2 h. The usual lecithin concentration present in the 35th to 38th wk of gestation can be determined with a coefficient of variation of 2-3% (n=30). Fetal lung maturity can be expected at a lecithin concentration above 4.7-5.1 mg/100 ml. The method compares well with the L/S ratio. Detailed data about clinical significance will be presented. Good precision accuracy and simple handling make enzymatic lecithin determinations suitable for routine use.

[Enzymatic lecithin determination in amniotic fluid for antepartal diagnosis of lung maturity - a multi-center study (author's transl)]. / Enzymatishce Lezithinbestimmung in fruchtwasser zur antepartalen Lungenreifediagnostik - Eine multizentrische Studie.

A new test-combination for the enzymatic determination of lecithin in amniotic fluid for the assessment of fetal lung maturity has been developed by Boehringer Mannheim. This test was evaluated by 12 hospitals and has been compared with the L/S ratio, the foam-test or the densitometric determination of lecithin. The assay is based on the hydrolysis of lecithin by phospholipase C which starts an enzymatic chain reaction in which NADH consumption if measured photometrically. The intra- and interassay precision were characterized by CV values below 10%. Average recoveries of lecithin were 95-102%. It is recommended to centrifuge the samples (10 min, 700 g) and to start the analysis as soon as possible after receipt of the specimen. The total amount of time required is 2 hours for a single determination. Batches of up to 10 samples require little extra time. An opened test-combination can be used for a maximum of 30 single determinations. Comparison of the quantitative enzymatic lecithin determination with other methods showed that the critical value for lecithin is 5.0 mg/100 ml. Above 5.1 mg/100 ml no case respiratory distress syndrome was observed. The good precision accuracy and the simple handling make the enzymatic lecithin determination suitable for routine use.