Bronchiolitis obliterans syndrome in heart-lung transplant recipients: Diagnosis with expiratory CT

PURPOSE: To determine the test performance and longitudinal evolution of ai r trapping for diagnosing bronchiolitis obliterans syndrome (BOS). MATERIALS AND METHODS: Over 7 years, 111 combined inspiratory and expirator y computed tomographic examinations were performed in eight healthy control subjects and 38 heart-lung transplant recipients. Functional impairment wa s assessed with the BOS classification. Receiver operating characteristic ( ROC) analysis was performed to determine the optimal threshold of air trapp ing to distinguish between patients with and those without BOS and to compu te sensitivity and specificity for diagnosing BOS. RESULTS: The extent of air trapping increased with BOS severity (P = .001). A threshold of 32% of air trapping is optimal for distinguishing between p atients with and those without BOS and provides a sensitivity of 83%, a spe cificity of 89%, and an accuracy of 88%. The prevalence of BOS and positive predictive value of air trapping increased with postoperative time, but th e negative predictive value of air trapping remained high throughout the st udy. Patients without BOS who had air trapping exceeding 32% of the parench yma were at significantly increased risk of developing BOS (P = .004). CONCLUSION: At the threshold of 32%, air trapping is sensitive, specific, a nd accurate for diagnosing BOS. Patients with air trapping below 32% are un likely to have BOS. Air trapping exceeding 32% may be an early indicator of future BOS.