Clinical features of subjects with an isolated FEV1 reduction

BACKGROUND: The clinical significance of an isolated reduction in forced expiratory volume in 1 second (FEV1; i.e., low FEV1, but normal forced vital capacity [FVC] and FEV1/FVC) has not been established. OBJECTIVE: To examine the clinical features of subjects with an isolated FEV1 reduction. METHODS: Clinical, spirometry and radiological data were retrospectively collected from 15 192 subjects attending a medical check-up at the Health Promotion Center of the Asan Medical Center, Korea. Predicted spirometry values were calculated from the Korean reference equations, and the lower limit of normal was set at the 5th percentile. Subjects were divided into four groups: isolated FEV1 reduction, normal (normal FVC, FEV1 and FEV1/FVC), obstructive (low FEV1/FVC) and restrictive (low FVC and normal FEV1/FVC). The groups were compared in terms of clinical characteristics. RESULTS: Of the 15 192 subjects, 323 (2.1%) had an isolated FEV1 reduction, 10 591 (69.7%) were normal, 951 obstructive (6.3%) and 3327 (22.0%) restrictive. The isolated FEV1 reduction group had a higher proportion of subjects with smoking history (63.2% vs. 45.7%), radiology abnormalities (15.5% vs. 4.3%) and history of respiratory disease (8.4% vs. 3.0%) than the normal group (all P < 0.001). CONCLUSION: An isolated FEV1 reduction suggests abnormal spirometry, and further study is needed to evaluate whether these cases belong to the obstructive or restrictive group.