FEV1Q Minimal Clinical Important Difference in the COPDGene Study

Abstract Rationale The European Respiratory Society (ERS) and the American Thoracic Society (ATS) suggested the use of FEV1Q, defined as the ratio between the raw measurement and the sex-specific first percentile (0.5L for males and 0.4L for females) of forced expiratory volume in 1 second (FEV1), as a possible endpoint to express natural changes in lung function over time in adults. However, only limited evidence supports this proposal. Methods In the COPDGene Study, we aimed to evaluate the role of FEV1Q in assessing lung function changes from baseline (Phase 1) to the five year visit (Phase 2). Our goal was now to define the minimal clinical important differences (MCIDs) for FEV1Q that correlated with clinically meaningful end-points in all subjects and in different subgroups (Pre-COPD, COPD GOLD 1-4, COPD GOLD 2-4, and PRISm).For this purpose, we combined two different approaches, the average change (AC) and the change difference (CD) methods, to anchor variations in FEV1Q to multiple well-established clinical outcome measures, including St. George Respiratory Questionnaire (SGRQ), Modified Medical Research Council Dyspnea Scale (mMRC), and six-minute walk test (6MWT) distance. The primary analysis was performed on annualized FEV1Q changes, testing the hypothesis that differences greater than the MCID could predict all-cause mortality over a five-year interval (Phase 1-2). Results Phase 2 data was available for 5580 participants. In this group, FEV1Q MCIDs were relatively consistent among different subgroups, with the notable exception of PRISm, and converged towards 0.06 units/year, which correspond to a 24 and a 30mL/year decline in FEV1 in females and males, respectively. In Cox Proportional Hazard models adjusted for age, race, height, BMI, smoking status, and baseline FEV1, the MCIDs discriminated survival in the whole cohort (HR 1.53, 95%CI 1.35-1.73), in subgroups with COPD GOLD 1-4 (HR 1.64, 95%CI 1.39-1.93), COPD GOLD 2-4 (HR 1.62, 95%CI 1.37-1.92) and PRISm (HR 1.51, 95%CI 1.06-2.16), with model concordance (from 0 to 1) ranging from 0.67 to 0.72. Conclusions We defined an anchor-based MCID for FEV1Q decline of 0.06 units/year, corresponding to 24mL/year in women and 30mL/year in men. This extent of variation provided discrimination for all-cause mortality at five years. To our knowledge, no study has explored the prospective value of FEV1Q decline over time. Further investigations will be anyway needed to confirm our findings in different cohorts.

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