[Utility of normality low limit of spirometry in diagnosed COPD patients]

To evaluate the differences in COPD patients below the lower limit of normal (LLN) of the fixed ratio FEV1/FVC < 0.70 and those above this limit.

Cross-sectional study. COPD patients between 40 and 85 years old included in primary care clinical record database were randomly selected. Baseline and postbronchodilator spirometries were performed. Two groups of patients were established: FEV1/FVC<0.70 and ≤LIN (group1) and FEV/FVC<0.70 and >LIN (group 2). Sociodemographic, clinical, pulmonary obstruction, quality of life and attendance to health services variables were measured. The results of both groups were compared.

22.3% of the subjects were misdiagnosed FEV1/FVC < 0,70. Patients in group 2 (FEV1/FVC<0.70 y > LLN) are diagnosed at an older age, they have a lower exposure to tobacco and better pulmonary function (FEV1: 74.9% vs 54.6%). 35.5% of those patients belong to stage i of GOLD, vs 8.5%, this patients have an increased comorbidity. Patients in group 1 have more COPD exacerbations, worse quality of life, a higher BODEx index 2,3 (1.8) vs 1.1 (1.5); 55.1% of those patients were high risk patients (GoldC or Gold D). Diagnose before being 56 years old, an increased exposure to tobacco, the FEV>50%, and a lower comorbidity are associated with a greater chance of suffering COPD with LLN criteria.

We obtain two groups of patients with differentiated clinical characteristics if we use LLN. Subjects with FEV1/FVC<0.7 and >LLN have less obstruction, less severity and more comorbidity, suggesting the possibility of overdiagnosis or misdiagnosis. On the other hand, younger age at the time of diagnosis, higher tobacco consumption and more severe obstruction are related with FEV1/FVC >0.70 and