Clinical Significance of Bronchial Hyperresponsiveness to Adenosine 5-monophosphate in Bronchial Asthma

Abstract

Background and Objective: Airway hyperresponsiveness is a key feature of asthma and may be measured by the methacholine bronchoprovocation test (BPT) as a direct method, and adenosine monophosphate (AMP) BPT as an indirect method. The aim of this study was to evaluate the clinical significance of AMP BPT in the diagnosis of asthma compared to methacholine BPT. Method: Thirty-nine patients diagnosed as having bronchial asthma were enrolled. PC20 methacholine, PC20 AMP, and the pulmonary function test as well as the sputum induction test, blood sampling, and the allergic skin test were performed. Methacholine and AMP were prepared in a 0.9% sodium chloride solution to produce a range of doubling concentration of 0.075 to 50 and 0.4 to 400 mg/mL, respectively. Methacholine and AMP BPT were performed until FEV1 level had dropped by more 20% from the baseline or the maximum concentration of 50 and 400 mg/mL respectively. A cut-off value for PC20 of 25 mg/mL for methacholine and 400 mg/mL for AMP was used in our study for defining significant ronchial hyperresponsiveness to methacholine and AMP. Results: Methacholine BPT had a sensitivity of 79.5% and AMP BPT had a sensitivity of 48.7%. Only one subject among 8 patients with negative response to methacholine BPT showed positive response to AMP BPT. Thirteen (33%) among 20 patients with negative results on AMP BPT showed positive responses to methacholine BPT. PC20 methacholine level was significantly correlated with PC20 AMP level (r=0.48, P<0.05). There was an inverse correlation between the number of eosinophils in blood and PC20 methacholine as well as PC20 AMP (r=-0.42, P<0.05, and r=-0.42, P<0.05 respectively). Conclusion: AMP-BPT is less sensitive than methacholine BPT in the diagnosis of bronchial asthma, but may be a useful marker of airway inflammation in asthmatic patients.