LBC and SMT on gastric aspirates from preterm infants for the diagnosis of RDS

The use of some rapid tests on amniotic fluid and on tracheal/gastric aspirates may help estimating lung maturity in preterm infants and deciding whether to provide prophylactic or very early surfactant therapy. The lamellar body count (LBC) test is routinely used in obstetric clinical practice for the assessment of fetal lung maturity, as it is accurate and can be performed quickly at low cost. Quite recently, attempts have been made to assess LBC also in the gastric aspirate of newborn infants. The advantages of using gastric fluid instead of amniotic fluid to count lamellar bodies resides in its easiness of collection after birth and in the lack of blood contamination as opposed to amniotic fluid. However, the performance of LBC in gastric fluid has not yet been consistently determined.
On this basis, a Brazilian group has conducted a study to assess LBC in the gastric aspirate of newborn infants with and without respiratory distress syndrome (RDS) with the aim to evaluate its predictive power. The stable microbubble test (SMT) was also performed in the same samples as a comparison. Gastric aspirates are difficult to process because of their thickness and non-homogeneity. For this reason, the authors used DTT (dithiothreitol) as a diluent to liquefy samples efficiently avoiding centrifugation and reduction in LBC.
In total, 34 preterm infants with RDS and 29 without RDS, with a gestational age between 24 and 34 weeks, were included in the study. Gastric fluid was collected in the delivery room.
Overall, the best cut-off value for LBC to predict RDS was <42,000 lamellar bodies/µl, with a sensitivity of 92% (95% confidence interval, 95% CI, 73–100%) and specificity of 86% (95% CI 77–95%). The area under the receiver-operating characteristic curve was 0.928 (95% CI 0.86–0.99). Results observed with SMT were comparable to those reported with LBC. Of note, the application of both LBC and SMT in series, with the result considered as positive only if both tests were positive, showed a sensitivity of 100% and a specificity of 86%.
Overall, these findings suggest that LBC and SMT in gastric aspirates of newborn infants are comparable tests for the diagnosis of lung immaturity. Therefore, the decision to perform either LBC or SMT may depend upon the familiarity of each staff with these tests. The good sensitivity and specificity of both tests, associated to their simplicity and low cost, suggest that they may play a role in helping the neonatologist to decide for the administration of prophylactic surfactant to very immature infants, as well as for its very early administration to premature infants with respiratory symptoms suspicious of RDS. Moreover, even if this study has not the statistical power to reach definite conclusions, it might be possible that the association of LBC and SMT would improve the accuracy of the evaluation.

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