Comparison of histamine and methacholine for use in bronchial challenge tests in community studies

Measurement of bronchial reactivity is widely used in epidemiological surveys. Histamine has been compared with methacholine inhalation challenge in two samples of adults from a small town to determine which is the better agent for use in community studies. Increasing doses of histamine and methacholine were given, up to a maximum of 4 and 12 mumol respectively, according to the method of Yan et al, the provocative dose of agonist causing a 20% fall in FEV1 (PD20) being measured. More subjects had a measurable PD20 with methacholine than with histamine, both in a random sample of 108 subjects (25 v 11 subjects, p less than 0.01) and in an additional 95 subjects selected because of wheeze in the last 12 months (67 v 48 subjects, p less than 0.01). Side effects were mild with both agents but histamine caused voice change in more subjects (21% v 11%). Repeatability was assessed in a further group of subjects with wheeze in the last year. The 95% range for a single estimation of PD20 in subjects with a measured PD20 on at least one occasion was +/- 2.5 doubling doses for histamine (n = 25) and +/- 2.1 doubling doses for methacholine (n = 33). Thus methacholine has advantages over histamine for community studies of bronchial reactivity as it is possible to use doses that produce more PD20 measurements with fewer side effects.