To determine the diagnostic accuracy of the surfactant adsorption test (SAT) as a predictor for the need for surfactant replacement therapy in neonates with respiratory distress syndrome (RDS).

Amniotic fluid samples were collected from 41 preterm neonates with RDS treated with continuous positive airway pressure (CPAP) and 15 healthy control term neonates. Purified porcine surfactant served as a further control. Lamellar bodies and lung ultrasound score were also measured in a subset of the neonates treated with CPAP. Surfactant was administered according to the European guidelines, and clinical data were collected prospectively. Surfactant activity was measured as adsorption at the air/liquid interface and given in relative fluorescent units (RFU).

Surfactant activity differed among native porcine surfactant (median, 4863 RFU; IQR, 4405-5081 RFU), healthy term neonates (median, 2680 RFU; IQR, 2069-3050 RFU), and preterm neonates with RDS (median, 442 RFU; IQR, 92-920 RFU; P < .0001). The neonates who failed CPAP had lower surfactant activity compared with those who did not fail CPAP (median, 92 RFU; IQR, 0-315 RFU vs 749 RFU; IQR, 360-974 RFU; P = .0002). Differences between groups were more evident beyond 20-30 minutes of fluorescence; the 30-minute time point showed the highest area under the curve (0.84; P < .001) and the best cutoff level (170 RFU; specificity, 72%; sensitivity, 96%) for the prediction of CPAP failure. Surfactant activity at 30 minutes was significantly correlated with lamellar bodies (r = 0.51, P = .006) and lung ultrasound score (r = -0.39, P = .013).

This technique has the potential to be developed into a fast, simple-to-interpret clinical test. The SAT can reliably identify preterm infants with subsequent CPAP failure and shows promise as a screening test for surfactant replacement in preterm neonates.