Home Spirometry as a Clinical Trial Endpoint in People with Cystic Fibrosis: Results of the OUTREACH Study

RATIONALE: Change from baseline in FEV1 is a primary endpoint for many traditional clinical trials in cystic fibrosis (CF). Home spirometry holds promise as an endpoint for decentralized clinical trials, yet its cross sectional and longitudinal accuracy compared to office spirometry has never been evaluated prospectively in the research setting. OBJECTIVES: The primary objective was to estimate the accuracy of FEV1 measured by home compared to office spirometry using a repeated measures model. METHODS: Prospective, multicenter study comparing FEV1 measured by office vs. home spirometry in people with CF age ≥ 6. Over 3 months, participants performed office spirometry and home coached spirometry 3 times and home uncoached spirometry weekly. MEASUREMENTS AND MAIN RESULTS: 115 participants were enrolled at 19 U.S. sites. Compared to office spirometry, estimated mean home coached percent predicted (pp) FEV1 at Visit 1 was 1.46% lower (95% CI -2.46. -0.37) and home uncoached slightly lower still (mean -3.31, 95% CI -4.54, -2.16). However, there was no significant difference in the estimated 3-month change in ppFEV1 between office and home coached or home uncoached spirometry: difference -0.22 (-1.54, 1.24) and 0.81 (-0.84, 2.57), respectively. CONCLUSIONS: Cross-sectionally, mean ppFEV1 by home spirometry is lower than office measurements, reinforcing that these measurements are not interchangeable. However, the change in ppFEV1 from baseline, which would be used to evaluate a treatment effect in a clinical trial, was not significantly different between home and office spirometry, suggesting that home spirometry may be a promising endpoint for decentralized trials in CF.