Study Supports Use of Practiced Threshold for Diagnosing COPD

New study findings are supporting the use of the ratio of forced expiratory volume in 1 second to forced vital capacity (FEV₁:FVC) less than 0.70 to identify people at risk of clinically significant chronic obstructive pulmonary disease (COPD).

The study, published in JAMA, found that the 70% ratio of the 2 measurements of lung function proved as or more accurate than other thresholds for predicting COPD-related hospitalizations and deaths. The findings can have important implications for patient care, as the prevalence of airflow obstruction, a key feature of COPD, can vary by as much as 33% depending on which threshold is used.

“Diagnosis of airflow obstruction remains a major hurdle to improving care for patients with COPD,” said James Kiley, PhD, director of the National Heart, Lung, and Blood Institute Division of Lung Diseases, in a statement. “This validation of a fixed threshold confirms the usefulness of a simple approach for assessment of the disease.”

The researchers relied on 4 US general population—based cohorts, examining data from 24,207 participants aged 45 to 102 years who were enrolled from 1987 to 2000 and received follow-up through 2016. Presence of airflow obstruction was defined by a baseline FEV₁:FVC ratio less than a range of 0.75 to 0.65 or less than the lower limit of normal as defined by Global Lung Initiative reference equations (LLN).

During a mean follow-up of 15 years, 3925 participants experienced COPD-related events, including 3563 COPD-related hospitalizations and 447 COPD-related deaths. The optimal fixed threshold for COPD-related events was 0.71, which was not statistically significant from the 0.70 threshold and was more accurate than the LLN threshold.

“Of particular clinical interest was a sub-group analysis in ever smokers, who constitute the majority but far from all of COPD cases,” wrote the researchers. “Among ever smokers, the optimal ratio threshold was 0.70. In never smokers, the optimal ratio threshold was 0.74, but event rates were low and 0.70 still offered more accurate prediction compared with the LLN.”

No thresholds were more accurate than 0.70 across strata of sex of in analyses adjusted for sociodemographic and anthropometric characteristics, suggesting that the 0.70 threshold may be applicable to all adults.

According to the LLN threshold, 3646 (15%) patients had airflow obstruction. Comparatively, a fixed threshold of less than 0.66 led to the most similar prevalence (3576 participants). However, 540 (15%) of these patients did not meet the LLN classification, and 610 (17%) of those meeting the LLN classification were excluded.

A total of 6261 (26%) patients had FEV₁:FVC ratios less than 0.70, including all but 19 of patients who met the LLN classification.

Reference

Bhatt S, Balte P, Schwartz P, et al. Discriminative accuracy of FEV₁:FVC thresholds for COPD-related hospitalization and mortality. JAMA. 2019;321(24):2438-2447. doi: 10.1001/jama.2019.7233.