What does the L/S ratio test determine?

The L/S ratio, or lecithin/sphingomyelin ratio, is a crucial assessment in neonatology, specifically used to evaluate lung maturity in infants. This test measures the presence of surfactant in the amniotic fluid. Surfactant is a substance that reduces surface tension in the alveoli, preventing collapse and facilitating proper lung function.

A higher L/S ratio indicates a greater amount of lecithin, which is a component of pulmonary surfactant; thus, it reflects better lung maturity. Infants born with a low L/S ratio are at a higher risk of developing hyaline membrane disease (HMD), also known as neonatal respiratory distress syndrome, due to insufficient surfactant production. Therefore, the L/S ratio test serves as a predictor for the likelihood of respiratory complications in newborns, particularly those delivered preterm.

In contrast, the other answer choices do not accurately reflect the purpose of the L/S ratio test. The test does not measure metabolic function, heart function, or overall growth parameters of the infant, which are assessed through different tests and clinical evaluations. Thus, the L/S ratio is specifically linked to lung maturity and the associated risk of respiratory distress in neonates.