"Click test": rapid diagnosis of the respiratory distress syndrome

Appropriate and early treatment with exogenous surfactant has clinical and economic benefits for neonates with pulmonary surfactant deficiency. In order to rapidly and reliably identify such neonates, we have evaluated the shake and click tests, biophysical tests of surfactant function, using 0.2 mL samples of tracheal (TA) and gastric aspirates (GA). Samples from 181 neonates with a gestational age range of 24-40 weeks were shaken with 95% ethanol. If bubbles formed (positive shake test) they were examined in air-free water under a microscope. In a positive shake or click test, the bubbles rhythmically increase and then decrease in size, denoting the presence of active surfactant. The probability of the tests to predict clinical surfactant deficiency was analyzed. The latter was defined as respiratory distress syndrome or transient tachypnea of the newborn diagnosed by chest radiography and clinical criteria. The click test on TA from preterm infants was most accurate, with a 100% positive predictive value and specificity, and a 93% and 94% negative predictive value and sensitivity respectively. These values for GA were 73%, 84%, 97%, and 95%, respectively. The test is quick, simple, inexpensive, reproducible, and unaffected by contamination with blood. The accuracy of this test on TA in diagnosing surfactant deficiency in neonates would permit early and optimal treatment with exogenous surfactant. When performed on GA, the test could aid decisions regarding transfer of neonates to tertiary level care.