Clinical Chemistry
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Clinical Chemistry 19: 967-972, 1973;
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Clinical Chemistry, Vol 19, 967-972, Copyright © 1973 by the American Association for Clinical Chemistry

A Modified Procedure for Evaluation of the Lecithin/Sphingomyelin Ratio in Amniotic Fluid

Emily Coch 1, John S. Meyer 1, Gordon Goldman 1, and Gerald Kessler 1

1 Department of Pathology and Laboratory Medicine and the Department of Obstetrics and Gynecology of the Jewish Hospital of St. Louis, St. Louis, Mo. 63110.

We describe several modifications of the procedure originated by Gluck et al. [ Amer. J. Obstet. Gynecol. 109, 440 (1971)] for evaluation of amniotic fluid lecithin/sphingomyelin (L/S) ratios. The acetone-precipitation step is eliminated, resulting in a faster extraction procedure and higher concentrations of phospholipids. For faster thin-layer chromatography, we use silica gel-impregnated sheets of glass-fiber and a modified solvent system. For spot detection we use a noncorrosive bismuth subnitrate reagent that is specific for lecithin and sphingomyelin, and an iodine vapor method to confirm the L/S ratio. The bismuth spray also detects significant specimen contamination by phospholipids from plasma or erythrocytes. The L/S ratio is evaluated by visually comparing the relative size and color intensity of the lecithin and sphingomyelin TLC spots. An L/S ratio of 5 or more is consistent with mature pulmonary function and an L/S ratio of less than 2 suggests fetal pulmonary immaturity.


Key Words: choline-specific spray • clinical findings for L/S ratio • fetal pulmonary immaturity

Submitted on December 12, 1972
Accepted on May 26, 1973






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Copyright © 1973 by the American Association for Clinical Chemistry.