Thank you for your recent inquiry.
Unfortunately there is no available test for serum specific IgE to fentanyl of which I am aware. In addition, a literature search failed to turn up any lab offering this test. Therefore I am afraid the only testing procedure you can pursue is skin testing.
Fentanyl, as you know, has been reported to cause anaphylactic episodes, and skin tests have been used on several occasions to detect fentanyl allergy. Fentanyl, unlike other opiates, does not cause primary non-IgE-mediated release of histamine, and therefore skin testing to fentanyl is probably a valid way to detect IgE to this drug.
Several protocols have been used. I have copied below the most recent reference that I could find related to skin testing to fentanyl. If you do wish to proceed with skin tests, it would give you not only the concentration to use, but should refer you to a bibliography with other related studies using skin tests to identify IgE to fentanyl.
Thank you again for your inquiry and we hope this response is helpful to you.
Milojevic I et al
Anaphylactic reaction during general anaesthesia associated with positive skin test to fentanyl.
Anaesth Intensive Care. 2009 May;37(3):502-3.
Phil Lieberman, M.D.