AHR in asthma

Peat et al have previously shown that exercise and histamine challenges may define different groups of children, 2 and we have shown that longer term repeatability of a free running exercise provocation test is poor within a childhood population. 3 In adults quite considerable within subject variability in PD20 to methacholine has been observed during a 1 year period, 4 and a childhood population study found that methacholine PD20 varied by >4 doubling doses within the course of a year in 33% of the subjects. 5 We would suggest that more care should be taken to define the precise measure of AHR used before comments can be made about its sensitivity and specificity in an epidemiological survey.