An allergy is an abnormal reaction to an ordinarily harmless substance called an allergen. When an allergen (such as pollen) is absorbed into the body of an allergic individual that individual's immune system views the allergen as an invader and a chain reaction is initiated. White blood cells of the immune system produce IgE antibodies. These antibodies attach themselves to special mast cells causing a release of potent chemicals such as histamine. These chemicals cause generalized symptoms as well as localized reactions in any organ system of the body. The reactions may be acute, subacute, chronic, immediate or delayed, and may be caused by numerous offending agents, such as pollen, molds, dust, mites, animal dander, stinging insect venoms, foods, and drugs.
Allergy Testing: The optimum management of the allergic patient should include a careful history and physical examination and confirmation of the cause of the allergic reaction obtained from some of the testing methods.
Direct Skin Testing is used to identify offending allergens. These tests include, but are not limited to:
- Percutaneous (scratch, prick, or puncture): This test consists of placing a drop of allergen on the skin making a needle scratch, prick, or puncture through the drop and into the underlying epidermis. The number of tests required may vary widely dependent on the patient's age and degree of hypersensitivity. Rarely are more than 40 percutaneous tests required.
- Intracutaneous (intradermal): This test involves the injection of a small amount of one or more allergic substances (within a solution) between the epidermal and dermal layers of the skin. Intradermal testing is considered to be more sensitive but less specific than percutaneous testing for the detection of IgE antibodies. Testing for drug and insect sting sensitivity should always be done using intradermal testing. The number of intracutaneous tests may also vary from patient to patient. Rarely are more than 20 intracutaneous tests required. Intradermal testing from delayed hypersensitivity of the tuberculin type should not exceed six to eight tests.
- Patch (Application) Testing: This test involves application of the suspected allergen(s) to the patient's back, which are covered with dressings and allowed to remain in contact with the skin for 48 hours. The area is then examined for evidence of delayed hypersensitivity reactions. Patch testing with 20 to 30 allergens using a screening patch test will detect as many as 70% of all cases of allergies causing contact dermatitis.
- Photo Patch Test: This test uses ultraviolet light the suspected allergen is applied to a patch of skin and left on for 48 hours. If no reaction occurs, the area is exposed to a dose of ultraviolet light sufficient to produce inflammatory redness of the skin. If the test is positive, a more severe reaction develops at the patch site than on the surrounding skin.
Serum Allergy Testing (IgE) (RAST, MAST, FAST, ELISA, PRIST): These tests are essential alternatives for patients in whom skin testing is contraindicated or unacceptable. This includes, but is not limited to those individuals in whom direct skin testing:
1. May be impossible due to extensive dermatitis or marked dermatographism,
2. May be impossible as the patient may be unable to cooperate or stop using antihistamines,
3. May be impossible in children less than four years of age,
4. Has not been conclusive, and further diagnostic testing is necessary, or
5. Has been refused by the patient.
Specific IgE In Vitro Testing / IgE Concentration Food-specific Testing:
This test detects antigen-specific IgE antibodies in the patient’s serum. These tests are considered equivalent to percutaneous skin testing for inhalant allergens (pollens, molds, dust, mites, and animal danders), foods and other allergens.
Total Serum IgE Concentration: This testing modality is not indicated in most allergic patients, but may be indicated for those patients suspected of having allergic bronchopulmonary aspergillosis, immune deficiency disease characterized by increased IgE levels (e.g., Wiskott-Aldrich syndrome, hyper-IgE staphylococcal abscess syndrome), IgE myeloma, or pemphigoid. In addition, a total IgE level is indicated in the evaluation of asthmatic patients being considered for therapy with monoclonal antibody to IgE.
Serial dilution end point titration (SDET), Serial endpoint testing (SET), sequential incremental testing also known as Rinkel/Rinkel method: This test is a form of intradermal skin testing that uses increasing doses of antigen to determine the concentration at which the reaction changes from negative to positive (the “endpoint”). The test has been used for diagnosing allergic disorders, and is a potential alternative to other diagnostic tests such as skin prick testing or in vitro testing for this purpose. In addition, SET has been used to guide the initiation of immunotherapy, by using the endpoint dilution as the starting antigen dose.
Nasal cytogram is the microscopic study of nasal secretions used to determine whether a patient has an allergy to inhalants or food, or if an acute or chronic viral infection is present, resulting in rhinitis or otitis.
Bronchial Challenge Test: Histamine or methacholine is used to perform this test when it is necessary to determine if the patient has hyper-responsive airways. Volatile chemicals are used to perform this test when the allergy is encountered in an occupational setting.
Double Blind Food Challenge Test: With this test, the patient ingests the food to which sensitivity is suspected. Both the patient and the physician are "blinded." This is usually done at home, but in some instances of suspected extreme hypersensitivity, it may be performed in the office setting.
Sublingual provocation food testing dates back to 1944. The test consists of placing three drops of an allergenic extract under a patient's tongue and waiting 10 minutes for any symptoms to appear. When the physician is satisfied he has determined the cause of the symptoms, he administers a "neutralizing" dose, which is usually three drops of a diluted solution of the same allergenic extract. The symptoms are then expected to disappear in the same sequence in which they appeared. Advocates claim that if the neutralizing dose is given before a challenge test (for instance, eating a meal containing the offending food), the person will not have symptoms.
Nasal Challenge Test (Also called nasal mucous membrane test; nasal challenge/provocation test): This test has been proposed as a tool in the diagnosis of allergic rhinitis. It is performed to duplicate the patient’s main symptoms or signs by controlled exposure to a suspected antigen and is delivered by direct application to the nasal mucous membranes. Evaluation of the patient’s response to the allergen is recorded.
Conjunctival Challenge Testing (ophthalmic mucous membrane test): Allergenic extract is placed into the conjunctival sac of the eye, followed by observation for redness, itchiness, tearing of the eye, and other similar symptoms.
Cytotoxic Food Testing (Leukocytotoxic Test): This test involves the response of specially collected white blood cells to the presence of food extracts to which the patient is allergic.
Leukocyte Histamine Release Test (LHRT): Measures the amount of histamine released from the white blood cells in response to exposure to an allergen.
Rebuck Skin Window Test: A test of the inflammatory process in which the skin is abraded and a cover slip is applied to the abraded area. The cover slips are removed and replaced at intervals and examined for the presence of cells involved in the immune response.
Passive Transfer of P-X (Prausnitz-Kustner Test): Performed by injecting serum intradermally from a suspect allergic patient into a nonallergic patient and later challenging the injection site with antigens.
Antigen leukocyte cellular antibody test (ALCAT): A test that is purported to measure a patient’s food intolerances, e.g., through proprietary technology, an evaluation of the patient’s white blood cells response when exposed to a variety of different foods.
IgG Food and Environmental Testing IgG4 Antigen Levels: These tests are a subclass of immunoglobulin G. Selective deficiencies in one or more of the four IgG subclasses are seen in some patients with repeated infections. Measurements of IgG4 antibodies have been used in research settings to determine response to allergy treatments.
Mediator Release Test® (MRT®) involves the measurement of the aggregate release of inflammatory mediators from an individual's immunocytes after exposure to various food extracts and chemicals (e.g., food additives). A determination is made of the difference in volume of circulating immunocytes and plasma before and after an in vitro antigen challenge. For the Mediator Release Test®, portions of an individual's blood sample is incubated with various food extracts and food additives (typically 150 different substances). The degree of reactivity is determined by the degree of mediator release from the cells. A response, change in cellular and plasma volume, is thought to indicate a hypersensitivity reaction and results are used as a basis for modifying an individuals diet. The MRT® is one component of the Lifestyle Eating and Performance (LEAP®) Program of oligoantigenic dieting. This type of testing has been promoted for individuals with, among other conditions, irritable bowel syndrome, chronic fatigue syndrome, migraine headaches, and dermatologic conditions (e.g., eczema, dermatitis).
Allergy Therapy: Once the offending agent has been identified, treatment is managed by avoidance, medication, or immunotherapy.
Avoidance is the preferred treatment to eliminate the allergen, requiring a change of diet, occupation, or residence; discontinuance of a drug; or removal of a household pet. However, complete avoidance may be impossible.
Medication may provide symptomatic relief for the patient but, does not address the cause of the problem. Medications may include steroids, antihistamines, or decongestants.
Immunity has been defined as freedom from or protection against certain diseases. Conventional or traditional immunotherapy, desensitization, or allergy shots, are recommended for patients with moderate to severe symptoms throughout most of the year who do not respond adequately to medications, and whose symptoms are triggered by an allergen that is not easily avoided (such as pollens or house dust mites). Immunotherapy involves the repeated injections of allergenic extracts (tiny amounts of allergen) that are given over a period of three to five years. By gradually increasing the amount of extract, tolerance to the offending allergen will increase, and the patient's symptoms will be relieved. Gradual injections may begin once or twice weekly over a period of four to six months. After the maintenance dose is achieved, the interval between injections may range between two and six weeks. Immunotherapy may be administered continuously for several years. Suspensions for injection of airborne or insect venom allergens should be prepared for the patient individually and under physician supervision.
Rapid Immunotherapy: Drug, pollen, or venom Rush or Rapid Immunotherapy (RIT) is done if sensitivity has been established by history, anaphylactic shock, positive challenge testing, and/or positive skin testing. In cases where drug administration for treatment is essential and no alternative exists, RIT desensitization is done by increasing dosages of allergen through intravenous access or injections. In some situations, the patient is hospitalized to provide oxygen, epinephrine, and resuscitation equipment to promptly treat the patient for any life-threatening reaction; and, the allergen doses are increased over a one to three day period. RIT can be done in the office setting for a period of less than 8 (eight) hours, which includes an observation period following the last injection. Premedication of antihistamines and steroids are given the day before and the morning of RIT. Baseline spirometry may be performed in asthmatic patients. An example of RIT is when penicillin desensitization is used as an emergent need to prepare an allergic patient for treatment of bacterial endocarditis.
Provocative and Neutralization Therapy: This method has been purported as a test for allergies, foods, and environmental chemicals. Patients are exposed to test doses of substances, and observed for the presence of symptoms. Then a diluted version of the offending substance is given to relieve symptoms.
Sublingual immunotherapy (SLIT) targets absorption to the sublingual and buccal mucosa. Allergen preparations used for SLIT are held under the tongue for one to several minutes and then swallowed or spit out.
No allergy extracts for sublingual immunotherapy are currently cleared or approved by the U.S. Food and Drug Administration (FDA).
Topical: localized application of an allergen directly to the organ creating the allergy response, such as the nose for allergic rhinitis.
Urine auto-injections (autogenous urine immunization): In this treatment, a patient’s urine is collected and sterilized. It is injected into the donating patient and presumed to provide relief from allergy symptoms.
Repository emulsion therapy: This technique uses mineral oil and antigenic material. The water in oil emulsion provides a slower release of these materials providing protection for a prolonged period of time.