Anaphylaxis due to patent blue dye during lymphography, with negative skin prick test

We report here a case of anaphylaxis due to patent blue dye, which was administered to an adult female during a lymphographic intraoperative procedure. The patient was not atopic, and other possible causes of anaphylaxis (anesthetics, latex) had been carefully excluded through routine tests. The skin-prick test and patch test carried out with patent blue (PB) dye were negative, but the intradermal test with 100 microliters of the dye showed a remarkable positivity. There was no available commercial, specific IgE assay for PB dye, but the negativity of prick tests would exclude the involvement of an IgE-mediated mechanism. We want to highlight the possible danger derived from a dye that is considered inert, and that is now increasingly being used in surgical procedures.