Relationship between atopy and bronchial responsiveness to histamine in a random population

Although there are theoretical reasons to suggest that atopy might predispose to non-allergic bronchial hyperresponsiveness, previous studies have yielded conflicting results. We assessed this by determining the atopic status and bronchial responsiveness to inhaled histamine in 400 randomly selected college students. An atopy score was determined as the number of "+"s from a standard battery of seven allergy prick skin tests each graded from + to +, and the atopic status was graded as non-atopic (no +'s) mildly atopic (1 to 4 +'s), moderately atopic (5 to 8 +'s), or markedly atopic (greater than 8 +'s). Non-allergic bronchial responsiveness to inhaled histamine was measured with a standardized histamine inhalation test from which the histamine provocation concentration producing a 20% FEV1 fall (PC20) was calculated. The prevalence of bronchial hyperresponsiveness to histamine (PC20 less than or equal to 8 mg/ml) was 10.3% in the entire population. There was a progressive increase from 6.1% in the non-atopic group to 33% in the markedly atopic group (p less than 0.001). In 43 subjects with both measurable atopy score (greater than or equal to 1) and PC20 (less than or equal to 16 mg/ml), a regression of atopy score vs. log PC20 produced a small (r = -0.36) but significant (p less than 0.02) correlation. These data indicate a significant relationship exists between atopic status and increased non-allergic bronchial responsiveness to histamine. Although cause and effect cannot be inferred from this study, it is hypothesized that atopy is one factor, among others, which predisposes to non-allergic bronchial hyperresponsiveness.