Serum bilirubin is associated with a reduced risk of subsequent recurrent wheezing following acute respiratory syncytial virus bronchiolitis

Background: Bilirubin is a potent antioxidant and anti-inflammatory molecule that has been shown to ameliorate airway inflammation. We aimed to study whether serum bilirubin is protective and can predict the development of subsequent recurrent wheezing in infants with severe respiratory syncytial virus (RSV) bronchiolitis. Methods: The medical records of 188 infants who were hospitalized during an initial episode of severe RSV bronchiolitis at 6 months of age or less were retrospectively reviewed. Our main outcome of interest was the development of subsequent recurrent wheezing by the age of 3 years. Each infant's serum bilirubin concentration was extracted from their blood biochemical results. Results: Seventy-one (37.8%) infants developed recurrent wheezing by the age of 3 and 117 (62.2%) did not. The serum total bilirubin, unconjugated bilirubin, and conjugated bilirubin levels at hospital admission were lower in infants who developed recurrent wheezing as compared to those who did not (p < 0.001). The area under the receiver-operating characteristic curve of serum total bilirubin, unconjugated bilirubin, and conjugated bilirubin for the prediction of subsequent recurrent wheezing were 0.71 (95% confidence interval [CI], 0.64-0.78), 0.70 (95% CI, 0.63-0.78), and 0.67 (95% CI, 0.59-0.75), respectively. Higher admission serum total bilirubin levels were independently associated with a lower risk of development of subsequent recurrent wheezing (adjusted OR 0.17, p < 0.001). Conclusion: During the first episode of severe RSV bronchiolitis in infants <6 months of age, moderately higher levels of serum bilirubin are associated with a reduced risk of developing subsequent recurrent wheezing by 3 years of age.