It has long been believed that COPD is underdiagnosed; several factors contribute to this. COPD is often clinically indistinguishable from chronic asthma. The symptoms are similar: many asthmatics smoke or have smoked but are not necessarily smoke susceptible, and many patients with COPD have hyperreactive airways but are not necessarily asthmatic. Several studies have also shown that asthma, like COPD, is associated with an accelerated decline in lung function irrespective of smoking status .
The most likely reason for underdiagnosis, however, is that disabling COPD symptoms do not appear until the disease is well advanced and pulmonary function is significantly impaired. Wolkove and co-workers have shown that statistically significant changes in forced expiratory volume in 1 s (FEVi) do not necessarily represent important differences in patients’ symptoms. The same authors also demonstrated that the correlation between acute changes in spirometry values and dyspnea is weak . Thus, patients with an FEV1 that is significantly lower than the predicted normal value may not perceive symptoms related to airway limitation .