Prevalence of asthma-COPD overlap syndrome among primary care asthmatics with a smoking history: a cross-sectional study.

BACKGROUND

The overlap between asthma and chronic obstructive pulmonary disease (COPD) is an important clinical phenomenon. However, the prevalence of asthma-COPD overlap syndrome (ACOS) is not known.

AIMS: To investigate the prevalence of ACOS among asthmatic patients with a smoking history, and evaluate the factors predicting ACOS in this patient group.

METHODS

We investigated 190 primary care asthma patients with no previous diagnosis of COPD, but who were either current or ex-smokers, with a smoking history of at least 10 pack-years. Spirometry was performed on all the patients while they were taking their normal asthma medication. Patients were considered to have ACOS if their postbronchodilator forced expiratory volume in 1 s/forced vital capacity was < 0.70.

RESULTS

Fifty-two (27.4%) of the patients were found to have ACOS. Age ⩾ 60 years and smoking for ⩾ 20 pack-years were the best predictors of ACOS. If both of these criteria were met, the odds ratio (95% confidence interval) for ACOS was 6.08 (2.11-17.49), compared with the situation where neither of these criteria were fulfilled.

CONCLUSIONS

There is a high prevalence of ACOS among primary health care asthmatics with a positive smoking history but no previous diagnosis of COPD. In this population, age over 60 years and a smoking history of more than 20 pack-years were the best predictors of ACOS.