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

¹ Yale University School of Medicine, Department of Internal Medicine, New Haven, Connecticut; and ² Veterans Affairs Clinical Epidemiology Research Center, West Haven, Connecticut

Correspondence and requests for reprints should be addressed to Carlos A. Vaz Fragoso, M.D., Clinical Epidemiology Research Center, VA Connecticut Healthcare System, Mailcode 151B, West Haven, CT 06516. E-mail: carlos.fragoso{at}yale.edu

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.

Key Words: chronic obstructive pulmonary disease • FEV₁/FVC • lower limit of normal • mortality • respiratory symptoms

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject 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 (COPD) is unknown. What This Study Adds to the Field In persons aged 40–80 years, an FEV1/FVC less than LMS-LLN at the fifth percentile (LMS-LLN5) identifies those with an increased risk of death and prevalence of respiratory symptoms.