Guidelines for diagnosis of COPD requiring a ratio of the FEV1 to the forced vital capacity of less than 0.70 are now better supported by evidence, thanks to US research.

The threshold for the ratio of FEV1 to the forced vital capacity (FEV1:FVC) has, until now, been based on expert opinion, the study team points out in a paper in the Journal of the American Medical Association.

Data pooled from more than 24,000 older adults from four US general population-based cohorts was used to determine which of various FEV1:FVC thresholds best predicted COPD-related hospitalisation and death.

Thresholds of 0.65 to 0.75 for FEV1:FVC were examined, as well as the lower limit of normal, defined as the lower 2.5th percentile of a healthy reference group adjusted for age, sex, race and height.