Is an abbreviated bronchial challenge with histamine valid?

Investigators have validated an abbreviated protocol for testing nonspecific bronchial reactivity with methacholine. We performed a similar validation study with histamine, another bronchoprovocative agent known to induce airflow obstruction. Histamine is pharmacologically distinct from methacholine and, under some circumstances, may provide specific clinical and investigative advantages to methacholine. Twenty-four patients with a clinical history of asthma underwent bronchoprovocative testing using the standard histamine airway protocol recommended by the American Academy of Allergy, Committee on Standardization of Bronchoprovocation. In addition, two abbreviated histamine challenge protocols were tested using the same administration and testing equipment. The abbreviated protocols involved fewer dilutions and dosages of histamine than the standard histamine protocol but covered the same range of cumulative doses. The two abbreviated protocols differed only in the intervals for determination of FEV1 between doses of histamine (30 s vs 3 min). The sequence of these three protocols was randomized for each study subject and each airway challenge was separated by one week. The two abbreviated protocols took significantly less time to administer than the standard protocol--18 min vs 30 min vs 44 min. Both the provocative dose to cause a 20 percent decline in the FEV1 (PD20 FEV1) and the slope of the dose-response curve were not significantly different between the standard protocol and either of the two abbreviated protocols. Moreover, a high degree of agreement was observed between the two abbreviated protocols and the standard histamine protocol for both the PD20 FEV1 and the slope of the dose-response curve. These findings indicate that similar estimates of bronchial reactivity are obtained from either of the abbreviated protocols when compared with the standard histamine protocol.