PURPOSE: LLN values for the ratio of forced expiratory volume in 1 seconds to that in 6 seconds (FEV1/FEV6) are not available for European patients. Because the fixed cut-off ratio currently used present severe methodological limitations we propose a substitute equation taking into account variations of cut-off with age and sex.
METHODS: We computed the best cut-off value distribution equation instead of the single best ratio. In order to validate this methodology, we first showed that the cut-off distribution equation approach could work for the standard FEV1/FVC data for which ERS LLN data are available. We made the hypothesis that the methodology could be extended to the FEV1/FEV6 data. We studied prospectively 4713 controls (2427 males, 2286 females) and 1484 obstructive patients ( 941 males, 543 females) routinely refered to the PFT laboratory for testing, aged 20 to 95 . The best cut-off value distribution equation for FEV1/FVC (FEV1/FVCct) was compared to the FEV1/FVC ERS LLN equation by ROC curve analysis in function of age and sex. Analysis was performed on 10 years age intervals. As we found no significant difference we computed by the same methodology the relationship between the FEV1/FEV6 individual ratios and detection of obstruction according to individual FEV1/FVC ratios compared to their LLN.
RESULTS: The regression equations for FEV1/FVCct were not significantly different from the FEV1/FVC lln equations given by ERS . The best FEV1/FEV6 cut-off value distribution according to age was not sex dependent. A single regression equation was therefore computed: FEV1/FEV6ct = 78.5-0.1 × age. Sensitivity was 0.99, specificity 0.91. All discordant false negatives and positives were within 2% of the LLN reference value in terms of FEV1/FVC ratio.
CONCLUSION: An equation derived from the diagnostic of obstruction obtained from FEV1/FVC data, for which LLN are available, could be obtained for FEV1/FEV6 data, with a high level of confidence .
CLINICAL IMPLICATIONS: Routine FEV1/FEV6 data analysis can now take into account sex and age variations in a European population.
DISCLOSURE: Andre Capderou, No Financial Disclosure Information; No Product/Research Disclosure Information