FEV6 is an acceptable surrogate for FVC in the spirometric diagnosis of airway obstruction and restriction

We analyzed the FEV1/FEV6 and FEV1/FVC results of 502 consecutive patients in the spirometric diagnosis of airway obstruction. We also examined the agreement between FEV6 and FVC in the spirometric diagnosis of restriction. Technically acceptable test results were obtained from 337 subjects (67%). The sensitivity of FEV1/FEV6 for diagnosing airway obstruction as defined by FEV1/FVC was 95.0%; the specificity was 97.4%. When interpretations differed, the measured values were all close to the lower limits of the reference ranges. When analysis included +/- 100-ml variability in FEV1 and FEV6, the sensitivity increased to 99.5% and the specificity to 100%. The reproducibility of FEV6 was superior to that of FVC. These results suggest that FEV6 is an accurate, reliable alternative to FVC for diagnosing airway obstruction and that FEV6 is reasonably comparable to FVC for the spirometric diagnosis of restriction. FEV6 is more reproducible and less physically demanding for patients.