Is an Acceptable Surrogate for FVC in the Spirometric Diagnosis of Airway Obstruction and Restriction

We analyzed the FEV 1 /FEV 6 and FEV 1 /FVC results of 502 consecutive patients in the spirometric diagnosis of airway obstruction. We also examined the agreement between FEV 6 and FVC in the spirometric diagnosis of restriction. Technically acceptable test results were obtained from 337 subjects (67%). The sensitivity of FEV 1 /FEV 6 for diagnosing airway obstruction as defined by FEV 1 / 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 6 100-ml variability in FEV 1 and FEV 6 , the sensitivity increased to 99.5% and the specificity to 100%. The reproducibility of FEV 6 was superior to that of FVC. These results suggest that FEV 6 is an accurate, reliable alternative to FVC for diagnosing airway obstruction and that FEV 6 is reasonably comparable to FVC for the spirometric diagnosis of restriction. FEV 6 is more reproducible and less physically demanding for patients.