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Lecithin/Sphingomyelin Ratio, Amniotic Fluid

Methodology

Thin-Layer Chromatography (TLC)

Includes phosphatidylglycerol.

Performing Laboratory

Quest Diagnostics

Specimen Requirements

Container/Tube:  Screw-capped, plastic amniotic fluid container

Specimen:  6 mL of amniotic fluid

Transport Temperature:  Frozen

Collection Instructions:

Note:  If red blood cells are present, do not freeze before centrifuging at 140 x g for 10 minutes. Submit 4 mL supernatant fluid for analysis.

Reference Values

An L/S/ ratio of <2 suggests pulmonary immaturity. A ratio of 2-3 probably represents maturity, but an L/S ratio ≥3 is more reassuring.

Although PG may be detectable, pulmonary immaturity may be present if the L/S ratio is <2.

If the L/S ratio is ≥2 and PG is detectable, then pulmonary maturity is almost assuredly present.

Day(s) Test Set Up

Monday through Sunday

Test Classification and CPT Coding

83661 - fetal lung maturity assessment; lecithin sphingomyelin (L/S) ratio

84081 - phosphatidylglycerol