Background
Chronic obstructive pulmonary disease (COPD), characterized by persistent and progressive airflow limitation, is one of the major causes of morbidity and mortality worldwide, and its prevalence is increasing. COPD was previously regarded as a disease mainly characterized by breathlessness, but recently it has been reported that COPD has multiple symptomatic effects on health-related quality of life (HRQOL) [
1]. The severity of airflow limitation alone is not strongly correlated with HRQOL in COPD patients [
2]; therefore, comprehensive methods to evaluate the COPD-specific health status are needed.
Since 2011, Global Initiative for Chronic Obstructive Lung Disease (GOLD) adopted St. George’s Respiratory Questionnaire (SGRQ) as a new assessment tool for COPD patients considering their current respiratory symptoms and future risk of exacerbation. Currently, GOLD emphasizes HRQOL more than dyspnea alone and divides patients into more symptomatic (SGRQ ≥25) and less symptomatic (SGRQ < 25) patients based on previous clinical trials of long-acting bronchodilators [
3‐
5].
SGRQ is the most widely used and valid tool to evaluate the health status of COPD patients [
6] and is composed of 50 items with 76 weighted responses. The SGRQ scoring method is a bit difficult considering the amount of items and weighted responses required, and many COPD patients may find it difficult to complete without any help [
7]. Thus, the COPD Assessment Test (CAT) was developed to compensate for the complexity of SGRQ [
8,
9], and many studies which have evaluated the distribution of patients of GOLD grading classification according to the tool used to assess symptoms, found a different proportion of patients in each category using CAT score ≥ 10. With this background, GOLD recommended that the equivalent point of CAT for SGRQ of 25 is 10 [
8‐
12].
Clinical COPD Questionnaire (CCQ), which has a good correlation with SGRQ [
13,
14], is also thought to be a good instrument for assessing health status in COPD patients and is simple to use [
13]. However, although studies have reported that a CCQ score range of 1.0–1.5 is consistent with an SGRQ score of 25 [
14], until now, a clear CCQ cutoff point that is equivalent to an SGRQ score of 25 has not been determined. Furthermore, to date, the CCQ has not been sufficiently validated for evaluating health status in COPD patients in Asia [
15].
Therefore, the present study aimed (i) to assess whether the CCQ correlates well with other health status measures, lung function, and exercise capacity in Korean COPD patients, and (ii) to determine the CCQ cutoff point that corresponds well with the SGRQ cutoff point of 25, considered the standard representing more symptomatic patients.
Discussion
This study demonstrated that the CCQ is well correlated with other health status measurements including SGRQ, pulmonary function, and exercise capacity in Korean COPD patients. In our study, based on AUROC and CART analyses, the CCQ cutoff point that best corresponds to an SGRQ score of 25 was 1.4, which showed a better agreement rate and a higher classification power compared with other cutoff points.
GOLD recommends a comprehensive approach to assess and adequately manage symptoms in COPD patients and proposes the mMRC, CAT, and CCQ as interchangeable instruments for evaluation of health status. However, despite the potential clinical importance, the CCQ has not been widely used in clinical practice because there is no known precise CCQ cutoff point that correlates with an SGRQ cutoff point of 25 (considered the standard marker of more symptomatic patients) and also CAT has been preferred than CCQ because CAT is more widely implemented and recommended by GOLD. GOLD guidelines recently set a CCQ score range of 1.0–1.5 as being equivalent to an SGRQ score of 25 [
23], and recent studies suggest that the MCID value for the CCQ is approximately 0.4 [
28,
29]. However, this wide range seems to be impractical for use in the clinical setting. In addition, GOLD tends to focus more on the CAT rather than the CCQ.
Based on the findings of the present study, we suggest that a CCQ cutoff point of 1.4 is appropriate for dividing COPD patients into more symptomatic and less symptomatic patients. This was based on two analyses. First, the AUROC value for a CCQ cutoff point of 1.4 was the highest for agreement with an SGRQ score of 25. Second, a CCQ cutoff point of 1.4 was the best value to distinguish between an SGRQ score ≥ 25 and < 25 in the CART analysis. Consequently, a CCQ cutoff point of 1.4 was more concordant with an SGRQ cutoff point of 25, when compared to a CCQ cutoff point of 1.0. A low agreement was found with the SGRQ score of 25, when analysis was performed based on the CCQ cutoff point of 0.7, which corresponds to the CAT score of 10, based on CAT instead of SGRQ. This is in line with our previous report, which states that scores higher than a CAT score of 10, say 15, are more useful for assessment of the severity of symptoms [
30].
SGRQ is the most comprehensive disease-specific health status measure for COPD patients. However, because it is composed of 50 items, it is complicated for older COPD patients to answer without any help, and it takes a relatively long time to complete [
7]. The CCQ is thought to be an alternative to SGRQ and consists of only 10 questions assessed by a seven-point scale from 0 to 6. Because the CCQ is a simple tool, it takes about 2 min to complete, and subjects require no specific help to complete it [
13]. Along with its simplicity, the CCQ is a comprehensive tool to evaluate the health status in COPD patients because it has three domains (symptoms, functional state, and mental state), which means that the CCQ has psychometric properties that make it more useful [
13]. CAT, one of the symptom and HRQOL measurement proposed by GOLD, is one-dimensional tool, while CCQ is similar to SGRQ, which is the most comprehensive tool. Further, CCQ is more simple and easy to use than SGRQ. Since it contains the description for each score, patients can sassily respond to the questions by themselves. In this aspect, the present study is focused on CCQ.
This study confirmed the clinical efficacy of the CCQ for evaluating the health status of COPD patients. The CCQ correlates well with other health status measures, lung function, and exercise capacity. In addition, recent studies have suggested that an upward revised CAT as a symptom threshold could reflect health status more accurately than the existing CAT cutoff point (≥10), which was previously regarded as a surrogate of the SGRQ [
30‐
32]. Furthermore, our study determined a new and clear CCQ threshold for categorizing COPD patients as more or less symptomatic.
The present study has several limitations to consider. First, we conducted a cross-sectional analysis and did not investigate the predictive value of CCQ for lung function decline or future exacerbation risk. Second, although the CCQ consists of three domains (symptoms, functional state, and mental state), we did not record the three subcategories separately, but rather evaluated the CCQ as a whole. Third, only small number of women were included because of the low prevalence of female smokers, therefore there may be a limitations in external validity. Fourth, the gold standard of cutoff points to measure symptoms in COPD remained open for discussion. Thus, we also showed results of applying the CAT score of 10 as a standard for the symptom criteria. Lastly, the suggested CCQ cutoff point of 1.4 needs to be externally validated.