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Single items on the COPD Assessment Test were associated with different outcomes for smokers versus nonsmokers, which could offer more granular insight.

The COPD Assessment Test (CAT), widely recognized as a reliable tool for assessing COPD symptoms and guiding treatment strategies, comprises eight items scored on a scale of 0 to 5. It provides a total score ranging from 0 to 40 that reflects the overall impact of COPD on patients’ lives.

“Although this summation has been validated, a later analysis suggested that the first two questions (cough and phlegm) could be considered statistically independent from the last six questions. Since these two symptoms are likely to be related to active smoking, and given the high number of patients with COPD who still smoke, the question arises as to whether the results of CAT depend on smoking status,” wrote Peter Alter, MD, and colleagues, in a study published in the International Journal of Chronic Obstructive Pulmonary Disease.

“In addition, analyses of the single CAT items have already indicated that they carry a different amount of information with regard to different outcomes; for specific purposes, single questions might even be superior to the sum score.”

Dr. Alter and colleagues used data from the German COSYCONET cohort to explore how single items in the CAT correlate with clinical outcomes, particularly in relation to smoking status, comorbidities, and mortality risk.

Study Population & Methods

The authors analyzed data from 2,509 patients with COPD, including current smokers (n=625) and nonsmokers (n=1,884, comprising ex-smokers and never-smokers).

The researchers assessed comorbidities such as asthma, emphysema, cardiac diseases, and osteoporosis alongside standard lung function measures, including FEV1, FVC, and the transfer coefficient for carbon monoxide (KCO). Mortality was tracked over a six-year follow-up period. For statistical analysis, the investigators used Cox proportional hazard regression and logistic regression to evaluate relationships between CAT scores and clinical parameters.

Smoking Status, Risks, & Comorbidities

Current smokers differed from nonsmokers in several clinical characteristics, including less severe spirometric obstruction but greater reductions in KCO. Smokers scored higher on CAT items related to cough and phlegm but lower on dyspnea and activity limitations.

In nonsmokers, CAT items 4 (dyspnea) and 6 (confidence leaving home) were significantly associated with mortality risk, as was the total CAT score (all P<0.01). These associations were absent in smokers, likely due to variability in smoking-related symptoms, the researchers said.

Both groups demonstrated significant associations between the CAT total score and exacerbation risk. CAT items 2 (phlegm), 5 (activity limitations), 6 (confidence leaving home), and 7 (sleep disturbances) predicted COPD exacerbations in nonsmokers, as did the total score (all P<0.05). Among current smokers, items 2, 5, and 7 and the total score were linked to exacerbation risk (all P<0.05); however, item 1 (cough) was negatively associated with exacerbation risk.

Emphysema, indicated by a KCO less than 55%, was positively associated with items 4 (dyspnea) and 5 (activity limitations) in both groups but showed distinct patterns for other items between smokers and nonsmokers. The CAT total score and select items were significantly associated with asthma, cardiac disease, and osteoporosis, particularly in nonsmokers.

Clinical Implications

The authors concluded that analyzing single CAT items alongside the total score can provide a more nuanced understanding of COPD-related outcomes. For instance, item-specific responses may help identify comorbidities such as asthma or emphysema and stratify patients by exacerbation risk. In addition, the total score performed well as a general predictor of exacerbation risk in both smokers and nonsmokers, supporting its continued use in clinical practice.

The researchers added that their study’s cross-sectional design limits insights into causal relationships, and reliance on patient-reported comorbidities may introduce bias. Additionally, the surrogate marker for emphysema (KCO less than 55%) was validated only in a subset of patients.

“These findings might be of value in order to extract as much information as possible from a questionnaire that is well known and in widespread use,” Dr. Alter and colleagues concluded.