Interobserver reliability of the click test: A rapid bedside test to determine surfactant function

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Abstract
To determine the interobserver reliability of the click test, a rapid bedside test of surfactant function. One hundred samples (48 amniotic fluid, 28 gastric aspirates, 24 tracheal aspirates) were obtained from pregnant women, term and preterm infants managed at two perinatal centres. Gestational ages of the pregnancies or infants at time of sampling ranged from 24 to 40 weeks (mean±sd: 31±5). The click test was performed independently by two observers, with differing levels of experience, and blinded to each other’s results. Interobserver reliability was determined for samples classified as negative (no clicking bubbles), equivocal (a few clicking bubbles seen after 2 min of looking), and positive (clicking bubbles seen easily on first look). As negative and equivocal test results suggest surfactant dysfunction, these results were also combined to provide a dichotomised result. For samples classified as negative, equivocal and positive the interobserver agreement was 0.83, with agreement beyond chance shown by a quadratic weighted Kappa of 0.74 (95% CI=0.62–0.86). When negative and equivocal results were combined, the simple Kappa was 0.73 (95% CI=0.59–0.87). The click test has a high level of interobserver reliability. It is rapid, simple, accurate and able to be taught to medical and nursing staff with appropriate training. It has many potential applications including the prediction of fetal lung maturity in women with premature rupture of membranes, and in term and preterm infants who require the bedside testing of surfactant function.