Allergy to heparin: a new in vitro diagnostic technique.

Few descriptions of allergic reactions to heparin have been published, because these reactions are not well known, their prevalence is low and they are difficult to diagnose due to the lack of an in vitro test until now. We propose a new technique, the basophil activation test (BAT) for the diagnosis of these reactions. We performed in vivo and in vitro studies with heparin and its derivatives in two patients with heparin-induced acute urticaria. In both patients the results of prick tests with sodium and calcium heparin, enoxaparin and nadroparin with immediate reading were negative. Intradermal skin tests with immediate reading and reading at 48 and at 96 hours with calcium heparin, enoxaparin and nadroparin were positive in the immediate reading and after 48 hours in the first patient. The second patient showed positivity to nadroparin in the immediate reading. The same drugs were also tested using patch tests, with reading after 48 and 72 hours. The second patient showed positivity to nadroparin after 48 hours. The BAT was positive to enoxaparin in the first patient and revealed showed slight positivity to sodium heparin in the second patient. We consider the BAT to be a useful, safe and reliable test for the in vitro diagnosis of heparin allergy. This test avoids the use of provocation tests, which present a risk to the patient.