High resolution CT and bronchial reversibility test for diagnosing COPD

COPD is defined by airflow limitation that is not fully reversible and is associated with relevant risk factors. The diagnosis requires that other causes of chronic airflow limitation (CAL) be excluded. We assessed the diagnostic utility of high resolution thoracic CT (HRCT) and bronchodilator reversibility to assist in making a diagnosis of COPD.

We investigated 516 consecutive patients whose FEV1/FVC was less than 70% after inhalation of bronchodilator. HRCT was performed on all subjects and a final diagnosis was made only after 3 months of treatment and repeated spirometry.

Of 516 cases, 54.3% had COPD, 19.8% had asthma plus emphysema, and 13.2% had chronic asthma. The remaining 12.7% of patients with CAL had diffuse panbronchiolitis, bronchiectasis, bronchiolitis obliterans, or other miscellaneous diseases. In these minor diseases HRCT was essential in making a definitive diagnosis. The sensitivities of emphysema on HRCT and of absence of bronchodilator response for the diagnosis of COPD were 81% and 90%, respectively, and the specificities of the tests were 57% and 37%, respectively. In addition, HRCT revealed considerable heterogeneity of COPD. Emphysema was not recognized on HRCT in 18.6% of COPD patients. HRCT also revealed that 17.5% of COPD patients had other pulmonary complications including lung fibrosis compatible with usual interstitial pneumonia in the lung bases.

HRCT and the bronchial reversibility test had reasonable sensitivities but low specificities for diagnosing COPD. HRCT has some additional advantages in detecting heterogeneity and concomitant lung diseases in COPD.