Racial differences in predictive value of the lecithin/sphingomyelin ratio.

OBJECTIVE: Blacks are known to have lower rates of respiratory distress syndrome when rates are adjusted for gestational age and to be more responsive to antenatal glucocorticoid administration compared with nonblacks. These observations have been attributed to acceleration of the timing of lung maturation. An alternative hypothesis is that there are qualitative differences in the surfactants between races. STUDY
DESIGN: We reviewed the medical records of a cohort of 702 nonblack and 135 black infants delivered within 72 hours of lecithin/sphingomyelin ratio testing from the presurfactant era and compared respiratory outcome stratified by lecithin/sphingomyelin ratio.
RESULTS: Black newborns had less than one third the rate of respiratory distress syndrome (2.2% vs 8.0%, p < 0.01). To adjust for possible differences in maturational timing between races, the results were stratified by lecithin/sphingomyelin ratio. There were no cases of respiratory distress syndrome among black infants with a lecithin/sphingomyelin ratio > 1.2. The protective effect was evident across all strata of lecithin/sphingomyelin ratios (odds ratio 0.25, p = 0.04). Parallel, highly significant reductions in non-respiratory distress syndrome pulmonary morbidity were also noted across all strata of lecithin/sphingomyelin ratios (odds ratio 0.35, p = 0.02).
CONCLUSIONS: These differences in the predictive value of the lecithin/sphingomyelin ratio suggest that protection from respiratory distress syndrome must depend on factors independent of the ratio and that these factors differ between races. They also suggest that clinical interpretation of test results may be different between races.