12.4B: Diagnosis and Treatment of Allergy
Allergy testing can help confirm or rule out allergies, reducing adverse reactions and limiting unnecessary avoidance and medications.
Learning Objectives
- Describe how the skin prick test and the allergy blood test work to assess the presence of allergen specific antibodies in an individual
Allergy testing can help confirm or rule out allergies, reducing adverse reactions and limiting unnecessary avoidance and medications. Correct diagnosis, counseling, and avoidance advice based on valid allergy test results will help reduce the incidence of symptoms and medications and will improve quality of life. Earlier and more accurate diagnoses save costs due to a reduction in consultations, referrals to secondary care, misdiagnoses, and emergency admissions.
For assessing the presence of allergen-specific IgE antibodies, you can use two different methods: a skin prick test or an allergy blood test. Both methods are recommended by the NIH guidelines, are equally cost-effective, and have similar diagnostic value in terms of sensitivity and specificity. A healthcare provider can use the test results to identify the specific allergic triggers that may be contributing to symptoms.
Allergies undergo dynamic changes over time. Regular allergy testing for relevant allergens provides information on if and how patient management can be changed in order to improve health and quality of life. Annual testing is often the practice for determining whether allergies to milk, eggs, soy, and wheat have been outgrown. The testing interval is extended to two to three years for allergies to peanuts, tree nuts, fish, and crustacean shellfish. Results of followup testing can guide decision-making regarding whether and when it is safe to introduce or re-introduce allergenic food into the diet.
Skin testing is also known as “puncture testing” and “prick testing” because of the series of tiny punctures or pricks made in the patient’s skin. Small amounts of suspected allergens or their extracts are introduced to sites on the skin marked with pen or dye (the dye should be carefully selected, lest it cause an allergic response itself). Sometimes, the allergens are injected “intradermally” into the patient’s skin with a needle and syringe. Common areas for testing include the inside forearm and the back. If the patient is allergic to the substance, then a visible inflammatory reaction will usually occur within 30 minutes. This response will range from a slight reddening of the skin to a full-blown hive (called “wheal and flare”) similar to a mosquito bite in more sensitive patients. Interpretation of the results of the skin-prick test is normally done by allergists on a scale of severity, with +/- meaning borderline reactivity and 4+ indicating a severe reaction.
In contrast, an allergy blood test is quick and simple and can be performed irrespective of age, skin condition, medication, symptom, disease activity, and pregnancy. In addition, multiple allergens can be detected with a single blood sample. Allergy blood tests are very safe, since the patient is not exposed to any allergens during the testing procedure. The test measures the concentration of specific IgE antibodies in the blood.
Challenge testing is when small amounts of a suspected allergen are introduced to the body orally, through inhalation, or via other routes. Challenge tests are utilized most often with foods or medicines. If the patient experiences significant improvement while avoiding a suspected allergen, she may then be “challenged” by reintroducing it to see if symptoms can be reproduced.
Patch testing is used to help ascertain the cause of skin contact allergy (contact dermatitis). Adhesive patches, usually treated with a number of different commonly allergenic chemicals or skin sensitizers, are applied to the back. The skin is then examined for possible local reactions at least twice, usually 48 hours after application and then again two or three days later.
Traditional treatment and management of allergies consisted of simply avoiding the allergen in question. However, while avoidance of allergens may reduce symptoms and avoid life-threatening anaphylaxis, it is difficult to do for those with allergies to pollen or other airborne allergens. Several antagonistic drugs are used to block the action of allergic mediators or to prevent activation of cells and degranulation processes. These include antihistamines, glucocorticoids, epinephrine (adrenaline), theophylline, and cromolyn sodium.
Desensitization or hyposensitization is a treatment in which the patient is gradually vaccinated with progressively larger doses of the allergen in question. This can either reduce the severity or eliminate hypersensitivity altogether. It relies on the progressive skewing of IgG antibody production to block excessive IgE production seen in atopys. In effect, the person builds up immunity to increasing amounts of the allergen. Studies have demonstrated the long-term efficacy and the preventive effect of immunotherapy in reducing the development of new allergies. A second form of immunotherapy involves the intravenous injection of monoclonal anti-IgE antibodies. These bind to free- and B cell-associated IgE, signaling their destruction.
Key Points
- To assess the presence of allergen -specific IgE antibodies, you can use one of two methods: a skin-prick test or an allergy blood test.
- Challenge testing is when small amounts of a suspected allergen are introduced to the body orally, through inhalation, or via other routes.
- Patch testing is used to help ascertain the cause of skin contact allergy (contact dermatitis).
- Traditional treatment and management of allergies consisted of simply avoiding the allergen in question.
- Several antagonistic drugs are used to block the action of allergic mediators or to prevent activation of cells and degranulation processes.
Key Terms
- allergen : a substance that causes an allergic reaction
- antihistamine : a drug or substance that counteracts the effects of a histamine. Commonly used to alleviate the symptoms of hay fever and other allergies
- skin prick test : Skin-prick testing is also known as “puncture testing” and “prick testing” because of the series of tiny punctures or pricks made in the patient’s skin. Small amounts of suspected allergens or their extracts (pollen, grass, mite proteins, peanut extract, etc.) are introduced to sites on the skin marked with pen or dye.