Threshold for positivity and optimal dipyrone concentration in flow cytometry-assisted basophil activation test

Basophil activation occurs both in patients with immediate hypersensitivity reactions to anti-inflammatory drugs and in healthy controls in a dose-dependent manner. Our aims were to define the optimal basophil activation test (BAT) concentration and the threshold for BAT positivity for dipyrone.

From 45 patients with a positive history of an immediate hypersensitivity reaction to dipyrone, we found 20 patients with dipyrone-induced anaphylaxis demonstrating positive skin tests. All selected patients, as well as 10 healthy controls, were tested in vivo and in vitro. BAT was performed using Flow 2CAST technique with three low dipyrone concentrations: 25 µg/mL (c1), 2.5 µg/mL (c2) and 0.25 µg/mL (c3). The threshold for BAT positivity was established using receiver operating characteristics (ROC) curve analysis.

Using ROC curve analysis the highest area under curve, 0.79 (0.63-0.95) (P<0.01), was found for c3. When the highest stimulation indexes from the three concentrations for each patient were used, ROC curve analysis revealed an area under curve of 0.81 (0.65-0.96) (P<0.01), sensitivity and specificity were 0.70 and 1 and the optimal threshold value for BAT positivity was 1.71. Thirteen patients had a positive BAT for at least one of the tested dipyrone concentrations. All healthy controls presented negative BAT.

BAT might be a useful technique to diagnose dipyrone allergy, provided all three low dipyrone concentrations are used together. With an assay-specific threshold of 1.71, ROC curve analysis yields 70% sensitivity and 100% specificity.