METHODOLOGY: Tracheal aspirates were obtained from neonates on ventilatory support. The SM test was carried out on specimens of tracheal aspirate immediately after collection. Levels of SP-A in tracheal aspirates were determined by enzyme-linked immunosorbent assay (ELISA) method. The results of the SM test and SP-A level of the tracheal aspirates were compared against the clinical diagnosis of RDS based on clinical, radiological and bacteriological findings.

RESULTS: Both the median microbubble counts (6 microbubbles/mm2, range = 0-90) and median SP-A levels (100 micrograms/L, range = 0-67447) of infants with RDS were significantly lower than those of infants with no obvious lung pathology (P < 0.0001), and pneumonia (P < 0.0001). The SM test of tracheal aspirates had higher overall accuracy for the diagnosis of RDS than measurement of SP-A levels (94.6% vs 82.4%). When the receiver operating characteristic (ROC) curves of both tests for RDS were compared, the area under the ROC curve of the SM test was larger (0.9689) than that of the SP-A method (0.8965).