Background Pyrazolones are a major cause of immediate IgE-mediated reactions to drugs in many countries.
Objective The aim of the study was to evaluate a group of patients with this type of reaction by basophil activation test (BAT), focusing on the influence of the time since the reaction on the rate of positive results.
Methods The study included 51 patients with selective immediate allergic reactions to pyrazolones and 56 controls. Patients were defined by skin testing or a drug provocation test and BATs with pyrazolones were carried out in all cases. Patients who were BAT positive were followed-up for 30 months to establish the rate of decline in positive tests.
Results BAT was positive in 28 (54.9%) cases. BAT sensitivity was higher in those who were skin-test positive (85.7%) compared with those who were skin-test negative (33.3%). The time between the initial reaction and this study was significantly shorter in those who were skin-test positive (P=0.005) and those who were BAT positive (P=0.017). Follow-up of the BAT-positive patients showed a decrease over time, with 60% of these patients becoming negative after 6 months.
Conclusions BAT is a useful complement to skin testing for the evaluation of immediate allergic reactions to pyrazolones. Although not optimal, BAT sensitivity was also positive in patients with a negative skin test and it is a reasonable alternative in patients with severe reactions who may develop symptoms after skin testing. The time of performance of the test is critical to obtain a positive response.