The Ratio of FEV1 to FVC as a Basis for Establishing Chronic Obstructive Pulmonary Disease

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Abstract
Rationale: The lambda-mu-sigma (LMS) method is a novel approach that defines the lower limit of normal (LLN) for the ratio of FEV1/FVC as the fifth percentile of the distribution of Z scores. The clinical validity of this threshold as a basis for establishing chronic obstructive pulmonary disease is unknown. Objective: To evaluate the association between the LMS method of determining the LLN for the FEV1/FVC, set at successively higher thresholds, and clinically meaningful outcomes. Methods: Using data from a nationally representative sample of 3,502 white Americans aged 40–80 years, we stratified the FEV1/FVC according to the LMS-LLN, with thresholds set at the 5th, 10th, 15th, 20th, and 25th percentiles (i.e., LMS-LLN5, LMS-LLN10, etc.). We then evaluated whether these thresholds were associated with an increased risk of death or prevalence of respiratory symptoms. Spirometry was not specifically completed after a bronchodilator. Measurements and Main Results: Relative to an FEV1/FVC greater than or equal to LMS-LLN25 (reference group), the risk of death and the odds of having respiratory symptoms were elevated only in participants who had an FEV1/FVC less than LMS-LLN5, with an adjusted hazard ratio of 1.68 (95% confidence interval, 1.34–2.12) and an adjusted odds ratio of 2.46 (95% confidence interval, 2.01–3.02), respectively, representing 13.8% of the cohort. Results were similar for persons aged 40–64 years and those aged 65–80 years. Conclusions: In white persons aged 40–80 years, an FEV1/FVC less than LMS-LLN5 identifies persons with an increased risk of death and prevalence of respiratory symptoms. These results support the use of the LMS-LLN5 threshold for establishing chronic obstructive pulmonary disease.

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