Positive skin tests to Hymenoptera venom extracts confirm immediate hypersensitivity in the context of a positive sting reaction history and help identify specific insects to which a patient is allergic.
Venom protein extracts are used for diagnostic testing. Hymenoptera venom testing is usually performed with each of the five commercial venom extracts (i.e. bees, wasps, yellow jacket, yellow hornet and white faced hornet) available in the United States, because patients are often inaccurate with regard to identification of the “culprit” stinging insect.
Venom testing is usually performed initially with prick tests. If results are negative, intradermal (where a small amount of the allergen is injected under the skin of the arm) skin tests are performed beginning with a venom concentration around 0.001 μg/mL. If the skin tests at this concentration are still negative, the venom concentration is increased by 10-fold increments until a positive skin test occurs, up to a maximum concentration of 1.0 μg/mL.
Skin tests are often positive to several venoms even when there has been a reaction to only a single insect sting. This is because of the known cross-reactivities among the vespid venoms.
Skin tests can be negative, even in patients with convincing histories of sting reactions. Skin test findings may be negative during the first 6 weeks after a sting because of a refractory period. Skin testing should be repeated after 1 or 2 months in these patients.
Some patients with a positive history and a negative skin test do have venom-specific IgE antibodies in the serum that can be detected by serologic testing using a radioallergosorbent test.
The board-certified allergists follow the updated AAAAI allergy practice parameter for stinging insect hypersensitivity. It recommends that for patients who have had a severe systemic reaction to an insect sting and who have negative venom skin test, repeat skin testing or in vitro testing for venom-specific IgE antibodies should be performed before concluding that venom immunotherapy is not necessary.