Study supports current airflow-obstruction threshold for COPD diagnosis

By Megan Brooks

NEW YORK (Reuters Health) - 25/6/2019

A new study supports current guidelines stating that a diagnosis of chronic obstructive pulmonary disease (COPD) requires a ratio of the forced expiratory volume in the first second to the forced vital capacity (FEV1:FVC) of less than 0.70.

This fixed threshold is based on expert opinion and "remains controversial," the study team points out in a paper in JAMA today.

"For clinicians, our study supports the continued use of FEV1:FVC <0.70 for diagnosing airflow obstruction in COPD, and demonstrates the prognostic accuracy of this threshold for clinically significant COPD," first author Dr. Elizabeth Oelsner of Columbia University Medical Center in New York City told Reuters Health by email.

The researchers used pooled data from more than 24,000 older adults from four U.S. general population-based cohorts to determine the discriminative accuracy of various FEV1:FVC fixed thresholds for predicting COPD-related hospitalization and death.

The presence of airflow obstruction was defined by FEV1:FVC less than a range of fixed thresholds (0.75 to 0.65) or the lower limit of normal (LLN), defined as the lower 2.5th percentile of a healthy reference group adjusted for age, sex, race and height.

They found that the optimal fixed threshold for discriminating COPD-related events was 0.71 (C statistic for the optimal fixed threshold = 0.696). The discriminative accuracy of the 0.71 threshold was not significantly different than that of the 0.70 threshold (difference = 0.001), but it was more accurate than the LLN threshold (difference = 0.034).

"The 0.70 threshold provided optimal discrimination in a subgroup analysis of ever smokers and in adjusted models," the authors report.

"Uncertainty regarding how to diagnose COPD has posed significant problems for early detection and treatment. Simplifying and standardizing the diagnosis of COPD has the potential to improve diagnosis, clinical care, and clinical research for this common and under-diagnosed chronic lung disease," Dr. Oelsner told Reuters Health.

"We therefore aimed to provide robust evidence for the best threshold to diagnose COPD by comparing how well various thresholds predict hospitalizations and deaths from COPD. We found that the fixed threshold of 0.70, which is recommended by current guidelines, proved as accurate, or more accurate, than other thresholds," she said.

In a JAMA editorial, Dr. Joergen Vestbo of the University of Manchester in the U.K. and Dr. Peter Lange of Copenhagen University in Denmark note that like most other common chronic diseases, "COPD is heterogeneous with several different components and likely many different pathways leading to the disease, as illustrated by the different trajectories of FEV1 leading to COPD. In addition, although a better understanding is emerging of the genetics of COPD and the interactions of small airways disease and emphysema, further research is needed to define subsets of COPD based on mechanisms."

"While waiting," they add, "clinicians may be best advised to continue to use an old simple measurement, FEV1:FVC of less than 0.70, as an indicator of this complex disorder. Now, based on the findings reported in (this study), this simple measurement has better evidence backing its prognostic value."

SOURCE: http://bit.ly/2IJJy4I and http://bit.ly/2xcrYQb

JAMA 2019.

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