Antithymocyte globulin hypersensitivity in bone marrow failure patients.

We evaluated the predictive value of immediate epicutaneous (prick) skin testing in 36 patients receiving a heterologous protein of equine origin, antithymocyte globulin (ATG), for bone marrow failure. Three of the 36 patients had positive epicutaneous test results. Two of these three received ATG treatment; one died of anaphylaxis while the other was desensitized successfully. Intradermal skin tests revealed positive wheal-flare reactions to progressively increasing dilutions of ATG in 96% of patients tested. None of these patients suffered any anaphylactic symptoms during treatment. Nine patients who had received ATG were evaluated subsequently for the possible development of immediate epicutaneous reactions three to 12 months after treatment; one of the nine patients developed a positive epicutaneous skin test reaction. We recommend that all patients who are to be treated or re-treated with heterologous antisera should be tested using the epicutaneous technique and that patients with positive reactions should be desensitized.