Background: Response-dose ratio (RDR) and cumulative provocative dosage (PD) are useful indices reflecting airway responsiveness in asthma.
Objectives: To compare the diagnostic value of RDR and PD, by conducting leukotriene D4 (LTD4-BPT) and methacholine bronchial provocation test (MCh-BPT), in different asthma control levels.
Methods: Healthy subjects and asthmatic patients underwent LTD4-BPT and MCh-BPT, at 2-14-day interval. This entailed assessment of the distribution characteristics, correlation, and diagnostic value of PD inducing 20% fall in forced expiratory volume in one second (PD20FEV1) and the RDR, defined as FEV1 fall (%) at the final step divided by the corresponding provocative dosage.
Results: Twenty uncontrolled, 22 partly controlled, 20 controlled asthmatics, and 21 healthy subjects were enrolled. Log10RDR was positively correlated with log10PD20FEV1 in both BPTs (all P < 0.05). Poorer asthma control was associated with significantly lower PD20FEV1 and higher RDR (both P < 0.05). The differences in PD20FEV1 and RDR between partly controlled and controlled asthma were unremarkable (both P > 0.05). Compared with log10PD20FEV1, the log10RDR yielded similar diagnostic values in both BPTs. A lower percentile of RDR (≤ 25th percentile) was associated with higher baseline FEV1 (P < 0.05) and an increased proportion of well-controlled asthmatic patients. The combination of RDR and PD20FEV1 led to an increased diagnostic value compared with either parameter alone.
Conclusions: RDR is a surrogate of PD20FEV1 for BPTs in asthma. This finding was not modified by different asthma control levels or the types of bronchoprovocants.