To determine whether an FEF25-75 from a good flow-volume loop contour provides any additional information.
The total number of tests performed in 2004 by a University Hospital Pulmonary Function Laboratory were retrospectively analyzed. We discarded tests that did not meet ATS standards, duplicate tests, tests from races other than Caucasian or African-American, or age > 80 years. The remaining 871 tests were categorized according to obstruction or non-obstruction and the FEF25-75 defined as normal or low according to the NHANES III predictive equations (age ≤ 80 years).
The Table shows the results. Of the 303 tests defined as obstructed by ratio of FEV1 to FVC, SVC (if available) or FEV6, 31% had a normal FEF25-75. Of the 568 non-obstructed tests, 7% had an abnormal FEF25-75. However, only 15 of these tests, or approximately 3%, had flow-volume loop contours that provided a reliable FEF25-75.
Only 3% of the FEF25-75 provided potentially new information. However, this is the expected value for false positives. The FEF25-75 was normal in 31% of the obstructed tests where it would be expected to be abnormal.
Obstruction is generally detected by using the FEV1/FVC, FEV1/SVC, or the newer FEV1/FEV6 ratio. Analyzing the FEF25-75 does not provide any additional useful information.
Numbers (%)ObstructedNon-ObstructedFEF Normal93 (31%)531 (93%)FEF Low210 (69%)37 (7%)
Jason Williams, None.