A Comparison of Clinic Versus Home Spirometry in the CAPTAIN Study

Abstract

Rationale: Many respiratory consultations are currently taking place virtually due to the ongoing SARS-CoV-2 pandemic, while traditional lung function testing in clinic is difficult to perform. Therefore, there is increasing interest in whether home measurements of lung function could be used in place of clinic testing. However, little is known as to whether home spirometry accurately reflects clinic measurements, and whether it provides sufficient precision to inform treatment decisions. Therefore, we evaluated the agreement between home and clinic measurements of trough FEV1 using data from the CAPTAIN study. Methods: This Phase IIIA, double-blind, 24-52- week, parallel-group study randomized adults with uncontrolled asthma despite inhaled corticosteroid/long-acting β2-agonist therapy. Treatment: once-daily FF/VI (100/25, 200/25mcg) or FF/UMEC/VI (100/31.25/25, 100/62.5/25, 200/31.25/25, 200/62.5/25mcg) (ELLIPTA inhaler). Trough FEV1 and other spirometry measurements were taken in clinic at approximately the same time in the morning using a MasterScope device. Patients also measured trough FEV1 each morning at home using a peak flow meter (AM3 device);three measurements were performed at each time point, with the highest measurement recorded. We used the Bland-Altman method to assess agreement between clinic trough FEV1 and the average of the home trough FEV1 measurements collected on the same day and 2 days prior to the clinic measurement, at baseline and at Week 24 (post hoc analyses). Only patients with a value for both clinic and home trough FEV1 were included (baseline: n=2434, Week 24: n=2261). Results: Agreement between clinic and home trough FEV1 measurements was poor (Figure). At baseline, the lower and upper limits of agreement were -812 mL and 943 mL, respectively, while at Week 24 these were -771 mL and 980 mL, respectively. In total, 6% of patients were outside the limits of agreement at baseline (n=151) and Week 24 (n=143) (Figure). Conclusions: This comparison of home and clinic spirometry in the CAPTAIN study suggests that home spirometry performed with the AM3 device cannot be used as an alternative to clinic spirometry, and that caution should be exercised when using home spirometry data in research or clinical care. The reason for the lack of agreement between home and clinic trough FEV1 measurements is not clear. Possible explanations include the different devices and methodologies, and lack of supervision and coaching for home measurements. However, it is possible that home spirometry may provide different and potentially complementary information to clinic measurements. Further investigation is warranted.