PURPOSE: Recent literature sites the use of Forced Expiratory Volume in 1 second/Forced Expiratory Volume in 6 seconds (FEV1/FEV6)as a surrogate for FEV1/Forced Vital Capacity(FVC) in diagnosing obstruction, with an average sensitivity of 94%. The aforementioned studies were predominantly on white patient populations. It is the objective of this group to evaluate the same indices in an inner city black patient population.
METHODS: A total of 380 studies were obtained that met acceptability criteria as defined by the American Thoracic Society. Prediction equations for FEV1, FEV1/FVC and FEV1/FEV6 as established by Hankinson et al, were used for Predicted Normals as well as Lower Limits of Normal (LLN). Obstruction was diagnosed by ratios below the predicted LLN. Sensitivity, specificity, positive and negative predictive values (PPV and NPV) were calculated for the FEV1/FEV6 vs. the FEV1/FVC.
RESULTS: The FEV1/FEV6 showed a sensitivity of 92% and a specificity of 97% compared to the FEV1/FVC. It had a PPV of 93% and its NPV was 97%. On examination of the discordant results (There were 8 false positives and 9 false negatives), majority fell close to the lower limits of normal, and when obstruction was stratified for severity according to the ATS guidelines they fell under mild obstruction.
CONCLUSION: Our population shows good correlation between the FEV1/FEV6 and the FEV1/FVC in identifying obstruction. It becomes apparent however that the discordant results identified may pose a problem to subgroups of patients with mild obstruction or ratios close to the lower limit of normal, such as smokers 45 years old and above for whom office spirometry which relies on FEV1/FEV6 is a recommended screening tool.
CLINICAL IMPLICATIONS: Although the utility of FEV1/FEV6 as a surrogate for FEV1/FVC to identify obstruction in patients who might have difficulty meeting standard end of test criteria is supported by our data, the utility of FEV1/FEV6 as a screening tool where the primary population will be at or near normal, needs to be evaluated further.
DISCLOSURE: Roberto Dos Remedios, None.