Regular smokers are as much at risk of developing, and of dying from, chronic obstructive pulmonary disease (COPD) as they are from lung cancer. Chronic obstructive pulmonary disease, a narrowing of the airways in the lungs caused by chronic bronchitis, emphysema, or (very often) the co-occurrence of both conditions, is increasing in prevalence worldwide.

It is insidious in its early stages, and is often under-diagnosed; however, advanced COPD is a common cause of disability and premature death. Smoking cessation in the early stages of the disease can prevent its progression, and early diagnosis is important in encouraging patients to enrol on appropriate smoking cessation programmes.

Computed tomography (CT) scanning of the pulmonary system is being trialled for the early detection of lung cancer. It is known that the dysfunction of the small airways that is characteristic of COPD can often be detected from these scans.

A group of clinicians and researchers led by Onno Mets from the University Medical Centre Utrecht, Utrecht, The Netherlands has used an ongoing trial of low-dose chest CT screening for lung cancer to test whether this screening will also diagnose COPD in heavy smokers. In this study, which was ancillary to the Dutch and Belgian Lung Cancer Screening Trial, a sub-group of trial participants underwent lung function testing – the usual method of diagnosing COPD – on the same day as expiratory low-dose CT scanning along with the regular inspiratory CT scanning used to screen for lung cancer.

All participants were male, aged between 50 and 75, and current or former heavy smokers with no history of cancer. After excluding participants with CT errors or inadequate smoking history data, the study population consisted of 1140 men. CT images of the lungs were separated from the rest of the image data and filtered, and image attenuation measured in order to estimate the degree of air trapping, which is a measure of emphysema. Lung function tests included measures of forced expiratory volume in the first second (FEV1) and forced vital capacity (FVC), with the ratio FEV1/FVC expressed as a percentage; COPD was defined as a FEV1/FVC ratio less than 70%, with the severity of the condition indicated by FEV1.

Before screening, 3.6% of the sample participants had been diagnosed with emphysema and 8.2% with bronchitis; from the lung function tests alone, 437 (38%) of the participants met the criteria for a diagnosis of COPD. CT screening predicted 359 participants as positive for COPD, with 274 of these later found to have the condition. Of the 781 who were predicted as negative for COPD, 163 had positive diagnoses from the lung function tests. These results gave a sensitivity score of 63%; a specificity of 88%; a positive predictive value of 76% and a negative predictive value of 79%.

The AROC values, a measure of the predictive value of a test that takes both positive and negative prediction into account, were 0.87 (95% confidence interval 0.86-0.88) for participants who experienced symptoms of COPD at the time of testing and 0.78 (95% confidence interval 0.76-0.80) for those who did not, showing, not surprisingly, that the test was more accurate in symptomatic men.

The study authors concluded that low-dose chest CT scanning was not accurate enough in diagnosing COPD to justify introducing the test for detecting this disease alone. However, if the results of this fairly small study can be replicated, it will be useful to introduce an additional expiratory CT scan into any existing lung cancer screening programmes for heavy smokers. This would raise the radiation dose received by participants, but not significantly.

Reference

Mets, O.M., Buckens, C.F., Zanen, P and 11 others (2011). Identification of chronic obstructive pulmonary disease in lung cancer screening computed tomographic scans. JAMA 306(16), 1775-81 doi: 10.1001/jama.2011.1531