PC20 adenosine 5 '-monophosphate is more closely associated with airway inflammation in asthma than PC20 methacholine

Inhalation of a direct stimulus such as histamine or methacholine is genera lly used to measure bronchial hyperresponsiveness (BHR). Provocation with a denosine 5'-monophosphate (AMP), an indirect airway challenge, has been sug gested to be a better marker of airway inflammation than direct challenges. However, so far little information on this subject is available. The aim o f our study was to assess whether the concentration of AMP causing the FEV1 to drop by 20% (PC20) is more closely associated with inflammatory paramet ers in asthma than PC20 methacholine. In 120 patients with atopic asthma (m edian FEV1 81% predicted [pred], median age 27 yr), PC20 methacholine and P C20 AMP as well as sputum induction, blood sampling, and measurement of nit ric oxide in exhaled air were performed. PC20 methacholine was predominantl y predicted by FEV1 %pred (explained variance [ev] = 18%) with the percenta ge of peripheral blood monocytes being a weak additional independent predic tor (total ev = 23%). By contrast, PC20 AMP was predominantly predicted by the percentage of eosinophils in sputum (ev = 25%), while FEV1 %pred was on ly an additional independent predictor (total ev = 36%). PC20 AMP reflects more closely the extent of airway inflammation due to asthma than PC20 meth acholine.