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Assessment of Fetal Lung Maturity by Lamellar Body Count (LBC) in Comparison to the Fluorescence Polarization TDx FLM-II and L/S Ratio Methods

Christopher Williams, Pascale Akl and Kenneth E. Blick

Respiratory distress syndrome causes morbidity and mortality of the newborn and is most often associated with premature birth. Laboratory testing can be helpful in establishing fetal lung maturity (FLM) status in situations when premature delivery may be necessary. In addition, the rising incidence of late-preterm births at >34 and <38 weeks gestation and the associated increases in cost of preterm infant care indicate a need for better preterm delivery FLM assessment. Over the years, the laboratory's primary amniotic fluid FLM screening method included lung surfactant 1) using the lecithin/sphingomyelin ratio (L/S ratio) by thin layer chromatography and 2) the TDx FLM-II method, the latter method being automated and hence available in a timely manner on a 24/7 basis. The lamellar body count (LBC) on amniotic fluid has been shown in studies to be an alternative for FLM assessment however the level of agreement and associated diagnostic cutoffs with LBC with these other classic lung surfactant methods have not been firmly established on our hematology analyzer. We found our LBC method compared favourably with the TDx FLM-II method (LBC =0.990*TDx FLM-II – 3.01; R2 = 0.501) as well as with the classic "gold standard" L/S ratio (LBC =15.2*L/S - 3.36; R2=0.762) leading us to conclude that our LBC was an acceptable surrogate for the well-established and no longer available fluorescent polarization TDx FLM-II method for rapid FLM screening. In addition, based on these comparison studies, LBC cutoffs were as follows: Immature, <=20 k/mm3; Indeterminate, 21 to 49 k/mm3; and mature, >=50 k/mm3.