From the Guidelines
The recommended protocol for allergy testing in a laboratory setting involves a systematic approach beginning with skin tests, followed by blood tests when necessary, as this approach balances diagnostic accuracy with patient safety, according to the most recent and highest quality study 1. This protocol is based on the latest clinical practice guideline for allergic rhinitis, which recommends performing and interpreting specific IgE (skin or blood) allergy testing for patients with a clinical diagnosis of allergic rhinitis who do not respond to empiric treatment, or when the diagnosis is uncertain, or when knowledge of the specific causative allergen is needed to target therapy 1.
Key Steps in the Protocol
- Skin prick tests (SPT) should be performed first, where small amounts of suspected allergens are placed on the skin and the area is pricked to allow allergen penetration, as they are highly sensitive and specific, typically over 80% for both, and are considered more sensitive than blood testing 1.
- Results are typically read after 15-20 minutes, with a wheal diameter of 3mm or greater indicating a positive reaction.
- Intradermal tests may follow for increased sensitivity, injecting 0.02-0.05mL of allergen solution into the dermis, particularly when the prick test is negative and there is a high clinical suspicion for allergic sensitization to a particular allergen or if increased sensitivity is required 1.
- For patients unable to undergo skin testing due to skin conditions or medication interference, specific IgE blood tests (formerly called RAST) should be used, as they can provide useful information about the appropriate starting dose of selected allergens and can be used to define the allergens that should be used in allergen immunotherapy 1.
Precautions and Considerations
- Prior to testing, antihistamines should be discontinued for 3-7 days (depending on the specific medication), and certain antidepressants and corticosteroids may need adjustment, to minimize potential interference with test results.
- Emergency medications including epinephrine (0.3mg for adults, 0.15mg for children, via auto-injector), antihistamines, and corticosteroids must be readily available during testing to manage potential anaphylactic reactions, as serious adverse events such as anaphylaxis and death are extremely rare but can occur 1.
- The use of standardized allergens has greatly increased the consistency of skin test results for these antigens, and controlled studies have demonstrated the efficacy of immunotherapy for relevant allergens 1.
Benefits of the Protocol
- This protocol allows for direct observation of the body’s reaction to a specific antigen, is not affected by patient’s medications, and can be used for patients with skin conditions such as dermatographism or severe eczema, and for patients on β-blockers or with comorbid medical conditions that preclude skin testing 1.
- It also provides useful information about the appropriate starting dose of selected allergens and can be used to define the allergens that should be used in allergen immunotherapy, which can help to improve patient outcomes and quality of life 1.
From the Research
Allergy Testing Laboratory Protocol
The recommended protocol for allergy testing in a laboratory setting involves a combination of methods, including:
- Skin testing, which is used to exclude or confirm immunoglobulin E (IgE) mediated diseases, such as allergic rhinitis, asthma, and anaphylaxis, to aeroallergens, foods, insect venoms, and certain drugs 2, 3
- Two types of skin testing are used in clinical practice: percutaneous testing (prick or puncture) and intracutaneous testing (intradermal) 2, 3, 4
- Prick testing involves introducing a needle into the upper layers of the skin through a drop of allergen extract and gently lifting the epidermis up, while intracutaneous testing involves injecting a small amount of allergen into the dermis 2, 3
Skin Testing Methods
Different forms of skin testing are available, including:
- Individual prick testing
- Multiple prick testing
- Single intradermal testing
- Intradermal dilutional testing
- Blended techniques 4
- Each method has its own benefits and limitations, and the choice of method depends on the specific clinical situation 4
Safety Precautions
Skin testing can cause systemic allergic reactions, including anaphylaxis, and should only be performed by physicians with proper training in allergy and experience in treating anaphylaxis 5
- Caution should be taken to avoid creating a serious systemic reaction by injecting an injudicious amount of antigen into the skin, or in skin testing a patient whose medication profile puts them at increased risk 4
Diagnostic Value
Skin testing remains a valid and in some cases superior means of identifying inhalant allergy 4