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