The high prevalence of COPD among smokers suggests other possible inclusion criteria for screening, particularly because methacholine reactivity was a strong predictor of decline in lung function in the Lung Health Study . A study by Oxman et al indicated that exposure to occupational dust is a significant risk factor for COPD. Environment may also play a role: a population study in southern California showed that chronic exposure to air pollution has an independent adverse effect on lung function in male smokers and possibly in female smokers, and that this effect is additive to that of smoking .
As discussed above, age is also a risk factor for airway obstruction and is probably the key reason for underdiagnosis. Physicians are trained to evaluate symptomatic disease, but the dyspnea associated with COPD may not become evident to the patient until 50 years of age or later, and acute exacerbations of bronchitis may not occur until the 40s. The challenge, then, is to identify a reasonable age for COPD screening.