The St. George's Respiratory Questionnaire Definition of Chronic Bronchitis May Be a Better Predictor of COPD Exacerbations Compared With the Classic Definition

Abstract

Background: Chronic bronchitis (CB) increases risk of COPD exacerbations. We have shown that the St. George's Respiratory Questionnaire (SGRQ) CB definition identifies patients with a similar clinical phenotype as classically defined CB. Whether the SGRQ CB definition is a predictor of future COPD exacerbations is unknown.

Methods: We analyzed 7,557 smokers with normal spirometry and Global Initiative for Chronic Obstructive Lung Disease stage 1-4 COPD in the Genetic Epidemiology of COPD study with longitudinal follow-up data on exacerbations. Subjects were divided into classic CB⁺ or classic CB^-, using the classic definition. In addition, subjects were divided into SGRQ CB⁺ or SGRQ CB^-. Exacerbation frequency and severe exacerbation frequency were determined in each group. Multivariable linear regressions were performed for exacerbation frequency with either classic CB or SGRQ CB and relevant covariates.

Results: There were 1,434 classic CB⁺ subjects and 2,290 SGRQ CB⁺ subjects. The classic CB⁺ group had a greater exacerbation frequency compared with the classic CB^- group (0.69 ± 1.26 vs 0.36 ± 0.90 exacerbations per patient per year; P < .0001) and a greater severe exacerbation frequency (0.26 ± 0.74 vs 0.13 ± 0.46 severe exacerbations per patient per year; P < .0001). There were similar differences between the SGRQ CB⁺ and SGRQ CB^- groups. In multivariable analysis, both SGRQ CB and classic CB were independent predictors of exacerbation frequency, but SGRQ CB had a higher regression coefficient. In addition, SGRQ CB was an independent predictor of severe exacerbation frequency whereas classic CB was not.

Conclusions: The SGRQ CB definition identified more subjects at risk for future exacerbations than the classic CB definition. SGRQ CB was at least a similar if not better predictor of future exacerbations than classic CB.

Trial registration: ClinicalTrials.gov NCT00608764.

Keywords: COPD; chronic bronchitis; cough; exacerbations.

Figure 1

Percent breakdown of each of the four chronic bronchitis groups. SGRQ = St. George’s Respiratory Questionnaire.

Figure 2

Differences in exacerbation frequency across GOLD stages. Red, classic CB⁺ vs classic CB^–; blue, SGRQ CB⁺ vs SGRQ CB^–. Circles represent mean difference and error bars represent 95% CI. *P < .05 and †P < .0001 compared with classic CB^– or SGRQ CB^–, respectively, on multivariable linear regression. CB = chronic bronchitis; GOLD = Global Initiative for Chronic Obstructive Lung Disease. See Figure 1 legend for expansion of other abbreviation.

Figure 3

Differences in severe exacerbation frequency across GOLD stages. Red, classic CB⁺ vs classic CB^–; blue, SGRQ CB⁺ vs SGRQ CB^–. Circles represent mean difference and error bars represent 95% CI. *P < .05 and †P < .0001 compared with classic CB^– or SGRQ CB^–, respectively, on multivariable linear regression. See Figure 1 and 2 legends for expansion of abbreviations.

Figure 4

OR for exacerbation frequency ≥ 2/y. See Figure 1 legend for expansion of abbreviation.

Figure 5

OR for severe exacerbation frequency ≥ 1/y. See Figure 1 legend for expansion of abbreviation.