Consensus on how best to express bronchodilator reversibility (BDR) is lacking. We tested different BDR criteria against the null hypotheses that BDR should show no sex or size bias. To determine the best criterion for defining BDR, we hypothesized that clinically important BDR should be associated with better survival in respiratory patients compared with that of patients without BDR.
We used the first BDR test of 4,231 patients who had known subsequent survival status (50.8% male sex; mean age, 60.9 years; mean survival, 5.2 years [range, 0.1-16.5 years]). BDR for FEV1 was expressed as absolute change, % baseline change, and change as % predicted FEV1.
Having BDR defined from absolute change was biased toward men (male to female ratio, 2.70) and toward those with larger baseline FEV1. BDR defined by % change from baseline was biased toward those with lower baseline values. BDR defined by % predicted had no sex or size bias. Multivariate Cox regression found those with FEV1 BDR > 8% predicted (33% of the subjects) had an optimal survival advantage (hazard ratio, 0.56; 95% CI, 0.45-0.69) compared with those with FEV1 BDR ≤ 8% predicted. The survival of those with FEV1 BDR > 8% predicted was not significantly different from that of those with FEV1 BDR > 14% predicted but was significantly better than that of those with FEV1 BDR < 0.
We have shown that expressing FEV1 BDR as % predicted avoids sex and size bias. FEV1 BDR > 8% predicted showed optimal survival advantage and may be the most appropriate criterion to define clinically important reversibility.