A comparison of the shake test, optical density, L/S ratio (planimetric and stechiometric) and PG for the assessment of fetal lung maturity

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Abstract
Our aim was to determine the diagnostic accuracy and reliability of four tests for the assessment of fetal lung maturity (FLM): shake test, optical density at 650 nm (OD650), lecithin to sphingomyelin ratio (L/S) by planimetry and stechiometry, and presence of phosphatydylglycerol. Amniotic fluid was obtained from 74 patients at various gestational ages. The shake test and the OD650 were performed according to published methods L/S was determined by TLC (thin-layer chromatography) and the ratio assessed by planimetry and stechiometrically by measurement of organic phosphorus from the chromatographic spots. PG was assessed similarly by TLC. When correlated with gestational age at amniocentesis, all tests correlated positively: shake test (r = 0.46, p < 0.005); OD650 (r = 0.31, p < 0.005); planimetric L/S (r = 0.77, p < 0.005); stechiometric L/S (r = 0.52, p < 0.005) and PG (r = 0.54, p < 0.005). The diagnostic accuracy of each test was as follows: the shake test and the OD650 had a sensitivity of 50%, while the steciometric L/S had a sensitivity of 75%, the planimetric L/S and the presence of PG were 100%. All four tests demonstrated a specificity greater than 64%, the highest for the PG presence being (83%) and the shake test (86%). Predictive negative values for lung maturity were > 93% for all tests, with the highest for the planimetric L/S and presence of PG being (100%). The study confirms that the determination of L/S ratio is still superior to other tests in terms of overall diagnostic accuracy. In addition, it was found that presence of PG was highly associated with the absence of respiratory complications in the newborn.

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