The ratio of the forced expiratory volume in 1 second to the forced vital capacity (FEV1:FVC) at the recommended threshold of 0.70 effectively diagnosed individuals at risk for clinically significant COPD, a longitudinal study of more than 24,000 individuals has found.
Guidelines from respiratory societies have long recommended a diagnosis of airflow obstruction when the FEV1:FVC is less than 0.70, but no rigorous, population-based studies have been conducted to support this recommendation, wrote Surya P. Bhatt, MD, of the University of Alabama at Birmingham, and colleagues.
“The selection of a threshold for defining airflow obstruction has major implications for patient care and public health as the prevalence of airflow obstruction can vary by as much as 33% depending on which threshold is selected,” they said.
In a study published in JAMA, the researchers reviewed data from 24,207 participants in the National Heart, Lung, and Blood Institute Pooled Cohorts Study to assess the accuracy of different thresholds in predicting COPD events in a large, multiethnic, U.S. population. All participants underwent spirometry; the average age at spirometry was 63 years, and 54% of the patients were women. Patients were enrolled during 1987-2000 and received follow-up longitudinally through 2016.
Overall, 3,925 participants experienced COPD-related events during an average of 15 years of follow-up (more than 340,757 person-years). These events included 3,563 hospitalizations and 447 deaths related to COPD.
The researchers compared three thresholds for FEV1:FVC ratios: a fixed optimal threshold of 0.71, a lower limit of normal (LLN) defined as 0.034, and the currently recommended 0.70.
The optimal 0.71 was not significantly different from the recommended 0.70 but was significantly more accurate than the LLN of 0.034. In addition, the 0.70 value was the optimal predictor in a subgroup analysis of ever-smokers and in multivariate analysis.
The findings were limited by several factors including the use of prebronchodilator spirometry, lack of adjustment for medication use, and limitation of outcomes to COPD mortality or clinical events mainly caused by COPD, which might exclude patients with mild to moderate disease, the researchers noted.
However, ” to help clinicians identify patients at increased risk for significant COPD, they said.
Lead author Dr. Bhatt disclosed a National Institutes of Health grant, consulting fees from Sunovion and research funds from Proterix Bio. The study was supported by grants from multiple agencies of the National Institutes of Health, including the National Heart, Lung, and Blood Institute, the National Institute of Neurological Disorders and Stroke, and the National Institute on Aging.