Amniotic Fluid Lamellar Body Count: Cost-effective Screening for Fetal Lung Maturity PAMELA S. LEWIS, MD, MICHELE R. LAURIA, MD, JEFFERY DZIECZKOWSKI, MD, GREGORY O. UTTER, MD, AND MITCHELL P. DOMBROWSKI, MD Objective: To create a highly specific cascade testing scheme for fetal lung maturity using the lamellar body count, lecithin/sphingomyelin ratio (L/S), and phosphatidylglyc- erol. Methods: A nondedicated hematology analyzer (Sysmex NE 1500, Toa Medical Electronics, Los Angeles, CA) was used to determine the lamellar body counts of 209 unspun amniotic fluid specimens. Maximally specific lamellar body count cutoffs for biochemical maturity and immaturity were determined using receiver operating characteristic curves. Biochemical lung maturity was defined as either a mature L/S ratio or phosphatidylglycerol. Biochemical lung imma- turity was defined as both an immature L/S ratio and an immature phosphatidylglycerol. Results: A lamellar body count of less than 8000 (n  17) was 100% specific for biochemical lung immaturity (positive predictive value  100%, negative predictive value  86%). A lamellar body count of greater than 32,000 was 98% specific for biochemical lung maturity (positive predictive value  99%, negative predictive value  63%). Conclusion: Testing only specimens where the lamellar body count was greater than 8000 and less than or equal to 32,000 for the L/S ratio and phosphatidylglycerol would preclude the need for 76% of all L/S and phosphatidylglyc- erol assays. Because the lamellar body count is quick, simple, and universally available, it could serve as an extremely cost-effective screening test for fetal lung matu- rity. (Obstet Gynecol 1999;93:387–91 © 1999 by The Amer- ican College of Obstetricians and Gynecologists.) The lecithin/sphingomyelin ratio (L/S) as developed by Gluck et al is one of the most widely used assays for the assessment of fetal lung maturity. 1 While it is a reliable test, it is expensive, time-consuming, and not universally available. Many institutions also incorpo- rate a phosphatidylglycerol assay to complete the fetal lung maturity profile. This test is also expensive, requir- ing time and trained laboratory personnel. The lamellar body count, also known as the lamellar body number density, was first described by Dubin in 1989. 2 The lamellar body is a surfactant-containing lamellated structure that is secreted by the type II pneumocyte (Figure 1). 3 Because lamellar body diame- ter is between 1–5 m, lamellar body counts can be determined using the platelet channel of a commercial cell counter. Therefore, it is a very quick, simple, and inexpensive test. The unit of measurement is number of lamellar bodies counted per microliter of amniotic fluid. As with platelets, it is reported as a value in the thousands. Several studies have shown lamellar body counts to be accurate predictors of fetal lung maturi- ty. 2,4 –11 Most of these studies have used spun fluid measured on an automated hematology analyzer and report a variety of values as indicative of maturity. Performing easy and inexpensive tests for lung ma- turity first, and more expensive tests only if initial tests are indeterminant has been advocated as a cost-effective method of screening for fetal lung maturity. 3,12,13 Our purpose was to determine if the lamellar body count is a reliable predictor of biochemical lung maturity. In addition, the utility of a cascade testing regime using lamellar body count as an initial step is examined. Materials and Methods Amniotic fluid specimens were obtained between Jan- uary and November 1996 by transabdominal amniocen- tesis on patients undergoing fetal lung maturity evalu- ation. All specimens received having more fluid than for our standard analysis were included. Only one spec- imen per subject was included. Lecithin/sphingo- myelin ratios and phosphatidylglycerol concentrations were determined using a modification of Gluck’s tech- nique that eliminates the steps of routine centrifugation, filtration, and acetone precipitation. 14 Studies done at From the Departments of Obstetrics and Gynecology, Pathology, and Internal Medicine, Wayne State University, Hutzel Hospital, and the Department of Obstetrics and Gynecology, Grace Hospital, and St. John Hospital and Medical Center, Detroit, Michigan. 387 VOL. 93, NO. 3, MARCH 1999 0029-7844/99/$20.00 PII S0029-7844(98)00416-5