Allergen bronchial challenge tests: variability and reproducibility of the early response

We evaluated allergen bronchial challenge tests (ABCTs) variability and reproducibility during 2-week intervals, respectively, in 28 and 14 Dermatophagoides pteronyssinus-sensitized patients. Increasing doses of Dpt (1.25 to 160 X 10(-3) mg) of lyophilized Dpt extract were administered at 20-minute intervals by doubling the previous dose. Dose-response curves (D-RC) were constructed for each test with the logarithm (base 2) of the allergen dose and the FEV1 in milliliters as ordinate. We analyzed different indices: the allergen doses causing a 15% decrease in FEV1 (PD15) and a 20% decrease in FEV1 (PD20), the slope of the curve beyond PD15, the overall slope, and the area under the parabolic curve. We found considerable intersubject variability in early asthmatic responses to Dpt ABCTs. Bronchoconstriction induced by allergen produced a specific D-RC for each individual. PD20 was significantly correlated with all the indices representing the whole D-RC (i.e., overall slope and area); moreover, PD20 was found on the steepest portion of the curve in 24 of 28 D-RCs. With the methodology used, we obtained a satisfactory reproducibility in a 2-week interval: the linear slope obtained by log base 2 transformation of doses was highly reproducible (p less than 0.001), as was area p under the parabolic curve. PD20 is significantly reproducible in a range of one doubling dose (twofold variation). The reproducibility of ABCTs over a short period permits solid arguments for their use in the evaluation of prophylactic treatment and in clinical research.