Development of a COPD severity score

ABSTRACT Objective: Treatment of chronic obstructive pulmonary disease (COPD) is based on symptom control. This suggests that COPD severity can be determined by analyzing treatment intensity. The objective of this analysis was to develop and validate a severity score for adult COPD based on treatments. Research design: Using principal components analysis, a COPD severity score was developed using data based on treatments extracted from an employer claims database (development group). Variables included were identified from literature review and clinical expert opinion. External validity was tested in a separate group of adult chronic bronchitis patients in whom principal components analysis was re-conducted and factor loadings were compared to the development group. Construct validity was tested by comparing the incidence of acute exacerbations of chronic bronchitis (AECB) in patients with high and lower severity scores. To illustrate the use of the COPD severity score, effectiveness of alternative AECB antibiotic treatments was compared in a separate patient sample categorized by severe versus mild/moderate COPD. Results: In the development group (n = 2068),principal components analysis produced a single main factor for severity scoring. Of the 12 variables contributing to this factor, the 6 with the highest factor loadings were treatment related. The factor performed similarly in the external validity group (n = 9127) as it did in the development group. In construct validity testing, severe COPD patients were 4 times more likely to have AECB episodes than mild/moderate patients. Patients with severe COPD and an AECB were more likely to fail treatment with antibiotics than those with mild/moderate COPD. Based on the COPD severity score developed, we found that treatment of patients with severe COPD and an AECB with fluoroquinolones was more likely to result in treatment failure than treatment with macrolides (OR = 2.01; p = 0.03). Conclusions: The analysis was successful in developing and validating a method to score COPD severity based on treatments. This method may prove useful in providing insights about the benefits of COPD treatments.