Study Supports Optimal Threshold for Diagnosing COPD

James P. Kiley, PhD

A new study provides evidence to support the use of a simple measurement for diagnosing clinically significant airflow obstruction, the key characteristic of of chronic obstructive pulmonary disease (COPD). 

The study, funded by the National Heart, Lung, and Blood Institute (NHLBI), part of the National Institutes of Health, was published online in the Journal of the American Medical Association. 

Approximately 16 million Americans have COPD, and it is estimated that millions more have the disease and do not know it.

In order to provide scientific evidence for the best threshold to diagnose COPD, researchers compared how well various FEV1/FVC ratio thresholds predict hospitalizations and deaths from COPD among 24,207 adults in the NHLBI Pooled Cohorts Study, which combined existing cohort studies supporting large-scale studies of COPD.

The NHLBI Pooled Cohorts Study harmonized and pooled data from four U.S. general population–based cohorts (Atherosclerosis Risk in Communities Study; Cardiovascular Health Study; Health, Aging, and Body Composition Study; and Multi-Ethnic Study of Atherosclerosis). Participants aged 45 to 102 years were enrolled from 1987 to 2000 and received follow-up longitudinally through 2016. These four cohorts collected spirometry and follow-up data for COPD-related clinical events.

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The diagnosis of COPD is based on a simple breathing test called spirometry. Spirometry measures the amount of air you can force out of your lungs in one second (forced expiratory volume in one second, FEV1) compared to the total amount of air you can force out of your lungs (forced vital capacity, FVC).

“A lower FEV1/FVC ratio indicates obstruction of airflow, but where to ‘draw the line’ between normal and abnormal levels to define and diagnose COPD is debated,” says James Kiley, PhD, director of the NHLBI Division of Lung Diseases. “Current recommendations define COPD by a FEV1/FVC ratio less than 70%; however, this cut-off or ‘threshold’ is based on the opinion of some experts rather than scientific evidence, and other experts have argued for a different threshold; this has led to controversy, inconsistent scientific reports, and confusion in clinical practice. These results provide evidence for the continued use of a less than 70% FEV1/FVC to define COPD and to identify adults at elevated risk of COPD-related morbidity and mortality, which simplifies diagnosis, clinical care, and future clinical trials for this under-recognized serious chronic lung disease.”

This validation of a fixed threshold confirms the usefulness of a simple approach for assessment of the disease, according to Kiley.

The researchers said establishing a diagnostic threshold that is easy to use not only is critical to improving the adoption of spirometry in primary care; it may also result in earlier detection and treatment of patients.