CT Scans Might Help Detect COPD

by Bruce Sylvester – Computed tomography (CT) scanning for lung cancer of men who are current or former heavy smokers also identified a significant proportion with chronic obstructive pulmonary disease (COPD),  suggesting that CT scanning might help detect COPD in the wider population, researchers reported in JAMA.

Onno  Mets, M.D., of the University Medical Center Utrecht, the Netherlands, and colleagues conducted a study of whether low-dose lung cancer screening CT scans could identify subjects with COPD. The study, conducted within an ongoing lung cancer screening trial, included prebronchodilator pulmonary function testing with inspiratory and expiratory CT scans (same day) of 1,140 male participants between July 2007 and September 2008.

They used the  pulmonary function tests as the reference standard for the COPD diagnostic accuracy of the CT scans.

The average age of participants was 62.5 years. There was data for self-reported respiratory symptoms from 1,085 subjects. The researchers found that 566 of the subjects were symptomatic and 519 were asymptomatic. Forty-one participants (3.6 percent) reported physician-diagnosed emphysema and 93 (8.2 percent) reported physician-diagnosed bronchitis.

Based on pulmonary function testing, the investigators classified 437 participants (38 percent) as having COPD.

The final diagnostic model for the study included 5 factors independently associated with obstructive pulmonary disease: CT emphysema, CT air trapping (an abnormal retention of air in the lungs), body mass index, pack-years (the number of packs of cigarettes smoked per day multiplied by the number of years the person has smoked), and smoking status.

Using this model, the researchers identified 274 subjects with COPD with 85 false-positives, a sensitivity of 63 percent, a specificity of 88 percent, and a positive predictive value of 76 percent, which corresponds to 63 percent (274 of 437) of all participants with COPD. These 274 participants comprised 54 percent (150 of 277) of all participants with mild obstruction, 73 percent (99 of 135) of all participants with moderate obstruction, and 100 percent (25 of 25) of all participants with severe obstruction.

The authors concluded, “Our study findings suggest several practical considerations. If the results of this study are validated and confirmed and are found to be generalizable, it may be reasonable to consider adding an expiratory CT scan to the (baseline) inspiratory CT scan for additional evaluation of COPD because this would improve diagnostic accuracy. Although an additional ultralow-dose expiration CT scan increases the radiation dose, this exposure is limited. The additional scan can be obtained within the 5 minutes needed for lung cancer screening, so a substantial amount of extra scan time is not required…..A screening test should have a high sensitivity to identify most of the participants with unsuspected disease, and the performance of our strategy at optimal accuracy is not sufficient for CT to serve as a COPD screening test.”