Application of the COPD Assessment Test (CAT) to Patients with Interstitial Lung Disease

Abstract

The COPD Assessment Test was recently developed to assess health status in patients with COPD. However, little was known about its application to patients with interstitial lung disease, so we examined the relationship between the COPD Assessment Test score and respiratory impairment including the clinical picture in subjects with interstitial lung disease. Data were collected retrospectively from 52 consecutive subjects with interstitial lung disease on admission to our facility. All subjects completed the COPD Assessment Test, in which a higher score represented a worse health status. They were also assessed by pulmonary function test, SpO2 during 6-min walk test, and arterial blood gases. The COPD Assessment Test score was negatively correlated with the percentage of predicted forced vital capacity, forced expiratory volume in 1 second, total lung capacity, diffusion capacity of the lung for carbon monoxide, and PaO2 (p = 0.0005, 0.005, 0.0002, 0.0005, and 0.002, respectively). Breathlessness was detected as the high scoring item, while phlegm and sleep were the last affected items. The COPD Assessment Test score was higher in subjects with oxygen desaturation in SpO2 (≥4%) during 6-min walk test (p = 0.0001) and in subjects on home oxygen therapy (p = 0.0007). More than 75% of subjects with oxygen desaturation during walking were classified into a medium or severer impact level of the COPD Assessment Test score, and subjects on home oxygen therapy were classified into a high or severer impact level. PaCO2 in room air and SpO2 at rest did not correlate with the COPD Assessment Test score. The reliability of items in the COPD Assessment Test was 0.87 by Cronbach’s α coefficient. Our results suggest that the COPD Assessment Test may be a candidate for evaluating the health status and impact of disease on patients with interstitial lung disease.