Usefulness of stable microbubble test of tracheal aspirate for the diagnosis of neonatal respiratory distress syndrome

Objectives: To compare the overall accuracy of the stable microbubble test (SM test) with measurement of level of surfactant protein A (SP-A) of tracheal aspirate for the diagnosis of respiratory distress syndrome (RDS). 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/mm,(2) range = 0-90) and median SP-A levels (100 mu g/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:he SP-A method (0.8965), Conclusions: This study showed that the SM test of tracheal aspirate was a useful bedside diagnostic test for RDS, It could be carried out at any time after birth on infants requiring ventilatory support.