A negative skin test would be helpful in the evaluation of an immediate hypersensitivity reaction to insulin. Unfortunately, a positive skin test is not helpful because approximately 40% of patients on insulin therapy can have a positive response in the absence of clinical allergy.
IgE and IgG to insulin also play a diagnostic role in various protocols but have no definitive diagnostic significance.
This is a desensitization protocol for insulin allergy from the textbook, "Patterson's Allergic Disease," edition 6, 2002, edited by Grammer and Greenberger, pages 360-2:
Possible insulin allergy as manifested by pruritus only. AAAAI.