Can the concentration of an allergen in a True Test (patch test) induce anaphylaxis and angioedema in a previously sensitized patient to the same allergen?

From the Guidelines

Patch testing with allergens in the TRUE test is generally safe and unlikely to cause anaphylaxis or angioedema, even in previously sensitized patients. The concentrations used in patch tests are specifically formulated to be low enough to detect allergic contact dermatitis (a delayed type IV hypersensitivity reaction) without triggering immediate type I hypersensitivity reactions like anaphylaxis 1. The allergens in patch tests are applied topically and remain localized on the skin surface with minimal systemic absorption. This limited exposure significantly reduces the risk of triggering severe systemic reactions.

However, while extremely rare, there have been isolated case reports of systemic reactions during patch testing. Patients with severe allergies, particularly those with a history of anaphylaxis, should inform their dermatologist before undergoing patch testing. Clinicians should always have emergency medications available, including epinephrine, antihistamines, and corticosteroids, as a precautionary measure 1. The benefit of patch testing in identifying specific allergens typically outweighs the minimal risk of severe reactions, making it a valuable diagnostic tool for contact dermatitis when performed under appropriate medical supervision.

Some key points to consider when performing patch testing include:

• Using standardized allergen extracts when available
• Selecting the appropriate skin testing device
• Interpreting and documenting results accurately
• Having quality assurance procedures in place
• Being prepared for potential adverse reactions, including anaphylaxis and angioedema 1.

It's also important to note that the sensitivity and specificity of patch testing are between 70% and 80% 1, making it a reliable diagnostic tool for contact dermatitis. Overall, the risk of anaphylaxis or angioedema from patch testing is extremely low, and the benefits of patch testing in identifying specific allergens outweigh the minimal risk of severe reactions.

From the Research

Anaphylaxis and Angioedema in Patch Testing

• The concentration of an allergen in a patch test can potentially induce anaphylaxis and angioedema in previously sensitized patients 2, 3, 4.
• Anaphylaxis is a life-threatening systemic reaction that can occur within one to two hours of exposure to an allergen, and its incidence is estimated to be 2.1 per 1,000 person-years in the United States 3.
• The management of anaphylaxis involves removal of the trigger, early administration of intramuscular epinephrine, and supportive care for the patient's airway, breathing, and circulation 3, 4.
• Patch testing can be used to diagnose allergic contact dermatitis, but it is not commonly associated with anaphylaxis or angioedema 5.
• However, it is possible that a high concentration of an allergen in a patch test could induce a systemic reaction, including anaphylaxis or angioedema, in a previously sensitized patient 6.

Risk Factors for Anaphylaxis and Angioedema

• Coexisting asthma, mast cell disorders, older age, underlying cardiovascular disease, peanut and tree nut allergy, and drug-induced reactions are associated with severe or fatal anaphylactic reactions 3.
• Patients with a history of anaphylaxis or angioedema are at increased risk of developing these conditions again in response to a patch test 2, 4.
• The use of epinephrine, antihistamines, and corticosteroids can help manage anaphylaxis and angioedema, but the effectiveness of these treatments is not well established 2, 3, 4.

Prevention and Management

• Patients undergoing patch testing should be monitored closely for signs of anaphylaxis or angioedema, and emergency equipment and personnel should be available in case of a reaction 3, 4.
• The concentration of the allergen in the patch test should be carefully controlled to minimize the risk of a systemic reaction 5.
• Patients with a history of anaphylaxis or angioedema should be advised to carry an epinephrine auto-injector with them at all times, and to seek medical attention immediately if they experience any symptoms of anaphylaxis or angioedema 3, 6.