Fixed ratio or lower limit of normal as cut-off value for FEV1/VC: an outcome study

Abstract

There is no consensus on the appropriate cut-off level for the ratio between forced expiratory volume and vital capacity (FEV(1)/VC) for the diagnosis of chronic obstructive pulmonary disease (COPD). Application of a fixed ratio of 0.7 carries the risk of false positive diagnoses in elderly subjects and false negative diagnoses in younger subjects. The use of the lower limit of normal (LLN) of an individually predicted value should eliminate this problem. There is insufficient information about the outcome of elderly subjects with an FEV(1)/VC < 0.7 but above the LLN. We report lung function (spirometry and lung clearance index, LCI), mortality and risk of cardiac events in relation to FEV(1)/VC in a population-based sample of men examined at age 55 years. We stratified subjects as having FEV(1)/VC ≥ 0.7 (N), <0.7 but > LLN (FR+) and <0.7 and <LLN (FR+LLN+). Hazard ratio for death was 1, 1.33 (0.94-1.9) and 1.71 (1.3-2.2), respectively, when adjusted for smoking and a number of cardiovascular risk factors. In contrast, there was no increase in the corrected hazard ratio for cardiac events. FEV(1) progressively declined and LCI increased from N to FR+ and FR+LLN+. Subjects with FEV(1)/VC ratio below 0.7 but above the lower limit of normal form an intermediate group with respect to lung function impairment and mortality rates. Careful evaluation of patient history and extended lung function testing may be warranted in subjects with FEV(1)/VC < 0.7 but above the lower limit of normal.

Keywords: Airflow obstruction; Chronic obstructive pulmonary disease; Diagnosis; Forced expiratory volume; Spirometry; Vital capacity.