Study objectives: To evaluate the use of the FEV1/forced expiratory volume at 6 s of exhalation (FEV6) ratio and FEV6 as an alternative for FEV1/FVC and FVC in the detection of airway obstruction and lung restriction, respectively.
Setting: Pulmonary function laboratory of the Academic Hospital of the Free University of Brussels.
Participants: A total of 11,676 spirometric examinations were analyzed on subjects with the following characteristics: white race; 20 to 80 years of age; 7,010 men and 4,666 women; and able to exhale for at least 6 s.
Methods: Published reference equations were used to determine lower limits of normal (LLN) for FEV6, FVC, FEV1/FEV6, and FEV1/FVC. We considered a subject to have obstruction if FEV1/FVC was below its LLN. A restrictive spirometric pattern was defined as FVC below its LLN, in the absence of obstruction. From these data, sensitivity and specificity of FEV1/FEV6 and FEV6 were calculated.
Results: For the spirometric diagnosis of airway obstruction, FEV1/FEV6 sensitivity was 94.0% and specificity was 93.1%; the positive predictive value (PPV) and negative predictive value (NPV) were 89.8% and 96.0%, respectively. The prevalence of obstruction in the entire study population was 39.5%. For the spirometric detection of a restrictive pattern, FEV6 sensitivity was 83.2% and specificity was 99.6%; the PPVs and NPVs were 97.4% and 96.9%, respectively. The prevalence of a restrictive pattern was 15.7%. Similar results were obtained for male and female subjects. When diagnostic interpretation differed between the two indexes, measured values were close to the LLN.
Conclusions: The FEV1/FEV6 ratio can be used as a valid alternative for FEV1/FVC in the diagnosis of airway obstruction, especially for screening purposes in high-risk populations for COPD in primary care. In addition, FEV6 is an acceptable surrogate for FVC in the detection of a spirometric restrictive pattern. Using FEV6 instead of FVC has the advantage that the end of a spirometric examination is more explicitly defined and is easier to achieve.