There is controversy regarding the diagnostic importance of the FEV1/FEV6. This study examined the FEV1/FEV6 and FEV1/FVC ratios and their relationship to other lung measurements to explain discrepancies.
First test spirometry (n=22,837) and concomitant lung volumes (n=12,040), and diffusion (n=14,154), were studied in adults. Four groups were examined. Group-I = reduced FEV1/FEV6 + normal FEV1/FVC (n=302). Group-II = normal FEV1/FEV6 + reduced FEV1/FVC (n=1,158). Group-III = both ratios reduced (n=6,593). Group-IV = both ratios normal (n=14,784). Of particular interest was the relationship of Groups I-II to each other, and to Group-III.
Although the agreement of the FEV1/FEV6 and FEV1/FVC (kappa=0.85) was good, 3.8% of obstructed patients only had a reduced FEV1/FEV6 (Group-I) while 14.4% only had a reduced FEV1/FVC (Group-II). These two groups of only one ratio reduced, when compared to the group with both ratios reduced (Group-III), clearly had milder abnormalities based on FEV1/FVC, FEV1, RV/TLC, TLC, and DLCO. The pair wise comparisons of these Group-I and II measurements to Group-III were significant (p<0.0001). Group-I when compared to Group-II, had a lower %predicted FEV1 (−5.2%, p<0.0001), %predicted FVC (−10.7%, p<0.0001), Expiratory Time (−6.7s, p<0.0001), %predicted IC (−13.1%, p<0.0001), and %predicted DLCO (−4.5%, p=.005), but higher FEV1/FVC (3.6%, p<0.0001) and %predicted RV/TLC (8.5%, p<0.0001). One hundred group-I patients had subsequent spirometry. 60% showed a reduced FEV1/FVC and compared to individuals with a normal FEV1/FVC ratio, they had longer expiratory times (3.5s vs. 1s, p<0.0001).
Overall, the FEV1/FEV6 is not as sensitive as the FEV1/FVC in diagnosing airways obstruction, but it identifies patients with true obstruction, rather than a false positive test. As an isolated abnormality, it identifies a group of milder obstruction whose condition is masked by greater air trapping and diffusing impairment with relatively shorter expiratory times.
The FEV1/FVC ratio should not be replaced as the standard for measuring airways obstruction. There is however additional benefit to inclusion of the FEV1/FEV6 ratio for diagnosing obstructive airways disease.
Zachary Morris, No Financial Disclosure Information; No Product/Research Disclosure Information