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A recent study showed that the COPD assessment test was reliable and responsive for assessing health status in fibrotic interstitial lung disease.

The COPD assessment test (CAT) is “a reliable, responsive and clinically relevant instrument for assessing health status” in patients with fibrotic interstitial lung disease (FILD), according to the authors of a study published in Respiratory Investigation.

Idiopathic pulmonary fibrosis (IPF) is a progressive FILD associated with a poor prognosis, typically resulting in a median survival of 2 to 4 years. Other forms of FILD share similar clinical trajectories, making HRQOL a key focus of management.

While the St. George’s Respiratory Questionnaire (SGRQ) is commonly utilized, its complexity limits routine use. The CAT offers a simpler alternative and has shown validity in IPF and connective tissue disease-associated ILD (CTD-ILD). However, data on its responsiveness and minimal clinically important difference (MCID) in these conditions were previously limited.

Toshiaki Matsuda and colleagues conducted a retrospective chart review of 358 patients to evaluate the reliability, validity, and MCID of the CAT across various FILD types, including IPF and CTD-ILD.

The initial sample included 501 patients with FILD, of which 382 underwent follow-up evaluation at 6 to 12 months from study baseline. Additional patients with pneumomediastinum and pneumothorax, respiratory tract infection, malignancy, and those who had undergone lung transplantation were excluded.

The final cohort included 358 patients, including 131 patients with IPF and 227 with non-IPF (119 with UC-ILD, 75 without, and 44 with surgical lung biopsy), 88 with CTD-ILD, 12 with NSIP, and 8 with CHP). Patients had an average age of 66.8 ±8.7 years and were primarily male (63.1%). At baseline, the mean CAT score was 12.1 ±8.3 points.

The CAT demonstrated excellent internal consistency (Cronbach’sα=0.898) and acceptable test-retest reliability (ICC=0.865) in stable patients. Construct validity was confirmed by significant associations between CAT scores and clinical variables, consistent across both IPF and non-IPF groups.

Responsiveness analysis showed moderate correlations between changes in CAT scores and changes in key clinical anchors (FVC, mMRC, and 6MWD), with no interaction effect based on IPF diagnosis. The CAT was sensitive to changes in health status, with greater CAT score changes corresponding to more significant shifts in clinical measures.

Construct validity and reliability were confirmed even 2 years after the initial assessment, with consistent results across both patients with or without IPF. The study also found moderate correlations between CAT scores and physiological measures, though the correlation with DLCO was weak, limiting its use as an anchor in this context.

The study highlights that responsiveness—CAT’s ability to detect changes in health status—is crucial, especially given the progressive nature of both IPF and non-IPF FILD.

“This is the first paper to evaluate the reliability, responsiveness, and MCID of CAT in patients with FILD using clinical practice setting data,” the authors said. “These results suggest that CAT could be a useful tool to help clinicians and other health care providers more fully understand the health status of patients with FILD at the time of clinical evaluation.”

However, this research revealed limited data on patients showing improvement, as most had stable or worsening health over the study period. While CAT shows promise, limitations include the retrospective, single-center design and the lack of standardization in treatment.

The authors cautioned that results may not generalize to other populations due to possible ethnic differences in health perception, and prospective studies are needed. Despite these limitations, CAT’s simplicity makes it a strong candidate for routine use, particularly compared with more complex tools like the SGRQ and K-BILD.