Response–Dose Ratio is a Surrogate of Cumulative Provocative Dosage for Bronchial Provocation Tests in Asthma

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 D 4 (LTD 4 -BPT) and methacholine bronchial provocation test (MCh-BPT), in different asthma control levels. Methods Healthy subjects and asthmatic patients underwent LTD 4 -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 (PD 20 FEV 1 ) and the RDR, defined as FEV 1 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. Log 10 RDR was positively correlated with log 10 PD 20 FEV 1 in both BPTs (all P < 0.05). Poorer asthma control was associated with significantly lower PD 20 FEV 1 and higher RDR (both P < 0.05). The differences in PD 20 FEV 1 and RDR between partly controlled and controlled asthma were unremarkable (both P > 0.05). Compared with log 10 PD 20 FEV 1 , the log 10 RDR yielded similar diagnostic values in both BPTs. A lower percentile of RDR (≤25th percentile) was associated with higher baseline FEV 1 ( P < 0.05) and an increased proportion of well-controlled asthmatic patients. The combination of RDR and PD 20 FEV 1 led to an increased diagnostic value compared with either parameter alone. Conclusions RDR is a surrogate of PD 20 FEV 1 for BPTs in asthma. This finding was not modified by different asthma control levels or the types of bronchoprovocants.