Lamellar body count and stable microbubble test on tracheal aspirates from infants for the diagnosis of respiratory distress syndrome.

Objectives: To evaluate the performance of lamellar body count in tracheal aspirates from intubated preterm babies to predict respiratory distress syndrome.

Design: Case-control study.

Setting: Three neonatal intensive care units.

Patients: Seventy-two patients not older than 3 days were included in the study, 38 preterm infants with respiratory distress syndrome, 16 preterms without respiratory distress syndrome, and 18 term infants. All required mechanical ventilation.

Interventions: Lamellar body count was performed in an automated cell counter. Tracheal samples were diluted in dithiothreitol without centrifugation and kept frozen at -20°C until use. Samples were placed in a dithiothreitol-containing test tube at a ratio of one part tracheal aspirate to six parts dithiothreitol solution, vortexed for 10 secs, and aspirated by the cell counter. Lamellar body count was performed using the platelet channel. All results were multiplied by seven. The stable microbubble test was done for comparison.

Measurements: Lamellar body count and stable microbubble test.

Main Results: Lamellar body count was significantly lower in the respiratory distress syndrome group compared with the non respiratory distress syndrome preterm group and also with the term group. The median and interquartile range obtained for lamellar body count were 38,500/μL (14,000-112,000) for the respiratory distress syndrome group, 822,500/μL (442,000-962,500) for the non respiratory distress syndrome preterm group, and 633,000/μL (322,000-1,608,000) for the term group (p < .001). The sensitivity and specificity of lamellar body count and stable microbubble test for the diagnosis of respiratory distress syndrome were calculated, taking into consideration the respiratory distress syndrome and the non respiratory distress syndrome preterm groups. Considering a cutoff point of 200,000 lamellar bodies/μL, lamellar body count sensitivity was 92.1% (95% confidence interval 78.6-98.3) and lamellar body count specificity was 93.8% (95% confidence interval 69.8-99.8). The area under the curve was 0.94 (95% confidence interval 0.84-1.00).

Conclusions: Lamellar body count and stable microbubble test can be rapidly and easily performed on tracheal aspirates and they seem to have very good performance for diagnosing respiratory distress syndrome in intubated patients.