Histamine challenge testing: comparison of three methods.
Non-specific bronchial reactivity is related to the severity of clinical asthma. Histamine challenge testing is increasingly used in association with questionnaires in epidemiological studies of the prevalence and morbidity of asthma in the community. The histamine challenge method described by Cockcroft et al is widely used and well standardised but it has disadvantages for epidemiological studies, being relatively slow and dependent on a supply of pressurised air. In this study we have assessed two simpler methods, one described by Yan et al and one by Mortagy, and compared these with the Cockcroft method. Twenty four adults with asthma were tested with each method in set order in a balanced design, and retested with each method in the same order. The Mortagy and Yan methods recorded PC20 or PD20 values on both occasions in all 24 subjects, but the Cockcroft method only 16 subjects. Repeatability, assessed as the 95% range for a single measurement, did not differ significantly, being +/- 1.94, 2.11, and 2.40 doubling concentrations for the Mortagy, Yan, and Cockcroft methods respectively. The Mortagy and Yan methods required less cumbersome equipment and took under 15 minutes to complete, compared with up to 45 minutes for the Cockcroft technique. The similar repeatability of all three methods in these subjects suggests that the two faster techniques are viable alternatives. The technical problems of standardising the Mortagy method lead us to conclude that, of the three methods compared, the Yan technique offers the greatest advantages for epidemiological studies.