[Airflow limitation in Brazilian Caucasians: FEV1/FEV6 vs. FEV1/FVC].

OBJECTIVE To evaluate the use of the forced expiratory volume in one second/forced expiratory volume in six seconds (FEV1/FEV6) ratio as an alternative to the FEV1/forced vital capacity (FVC) ratio in the detection of mild airway obstruction. METHODS Reference equations for the Brazilian population in 2006 were used in order to determine the lower limits of normality for the FEV1/FEV6 and FEV1/FVC ratios. The spirometry findings of 155 patients from 20 to 84 years of age were analyzed. All of the patients presented the following: a < 15% difference between predicted and observed FEV1/FVC ratio; an FEV1 > 60% of predicted; and an exhalation time of at least 6 s. The Brazilian Thoracic Society criteria for acceptability and reproducibility in spirometry were met. RESULTS Mean values (+/- SD) for FEV1/FEV6 and FEV1/FVC were 73 +/- 4% and 75 +/- 3%, respectively. Using the FEV1/FVC ratio, we identified airflow obstruction in 61 patients, compared with only 46 patients when we used the FEV1/FEV6 ratio, showing a sensitivity of 75% (p < 0.001). CONCLUSIONS The FEV1/FEV6 ratio has poor sensitivity and should not be used to replace the FEV1/FVC ratio in the diagnosis of mild airway obstruction.