| Skin allergy test | |
|---|---|
 An array of chemical allergens to be used in testing | |
| Synonyms | Skin prick test |
| Purpose | Diagnosis of skin allergies |
Skin allergy testing comprises a range of methods for medical diagnosis of allergies that attempts to provoke a small, controlled, allergic response.
A microscopic amount of an allergen is introduced to a patient's skin by various means: [1]
If an immuno-response is seen in the form of a rash, urticaria (hives), or anaphylaxis it can be concluded that the patient has a hypersensitivity (or allergy) to that allergen. Further testing can be done to identify the particular allergen.[ citation needed ]
The "skin scratch test" as it is called, is not very commonly used due to the increased likelihood of infection. On the other hand, the "skin scrape test" is painless, does not leave residual pigmentation, and does not have a risk of infection, since it is limited to the superficial layer of the skin.[ citation needed ]
Some allergies are identified in a few minutes but others may take several days. In all cases where the test is positive, the skin will become raised, red, and appear itchy. The results are recorded - larger wheals indicating that the subject is more sensitive to that particular allergen. A negative test does not conclusively rule out an allergy; occasionally, the concentration needs to be adjusted, or the body fails to elicit a response.[ citation needed ]
In the prick, scratch and scrape tests, a few drops of the purified allergen are gently pricked on to the skin surface, usually the forearm. This test is usually done in order to identify allergies to pet dander, dust, pollen, foods or dust mites. Intradermal injections are done by injecting a small amount of allergen just beneath the skin surface. The test is done to assess allergies to drugs like penicillin [5] or bee venom.
To ensure that the skin is reacting in the way it is supposed to, all skin allergy tests are also performed with proven allergens like histamine, and non-allergens like glycerin. The majority of people do react to histamine and do not react to glycerin. If the skin does not react appropriately to these allergens then it most likely will not react to the other allergens. These results are interpreted as falsely negative. [6]
The patch test uses rectangles of special hypoallergenic adhesive tape with different allergens on them. The patch is applied to the skin, usually on the back. The allergens on the patch include latex, medications, preservatives, hair dyes, fragrances, resins, and various metals. [7] Patch testing is used to detect allergic contact dermatitis but does not test for hives or food allergy. [8]
Also called an intradermal test, this skin end point titration (SET) uses an intradermal injection of allergens at increasing concentrations to measure allergic response. [9] To prevent a severe allergic reaction, the test is started with a very dilute solution. After 10 minutes, the injection site is measured to look for growth of wheal, a small swelling of the skin. Two millimeters of growth in 10 minutes is considered positive. If 2 mm of growth is noted, then a second injection at a higher concentration is given to confirm the response. The end point is the concentration of antigen that causes an increase in the size of the wheal followed by confirmatory whealing. If the wheal grows larger than 13 mm, then no further injections are given since this is considered a major reaction.[ citation needed ]
There are no major preparations required for skin testing. At the first consult, the subject's medical history is obtained and physical examination is performed. All patients should bring a list of their medications because some may interfere with the testing. Other medications may increase the chance of a severe allergic reaction. Medications that commonly interfere with skin testing include the following:
Patients who undergo skin testing should know that anaphylaxis can occur anytime. So if any of the following symptoms are experienced, a physician consultation is recommended immediately:
Even though skin testing may seem to be a benign procedure, it does have some risks, including swollen red bumps (hives) which may occur after the test. The hives usually disappear in a few hours after the test. In rare cases they can persist for a day or two. These hives may be itchy and are best treated by applying an over the counter hydrocortisone cream. [11] In very rare cases one may develop a full blown allergic reaction. Physicians who perform skin test always have equipment and medications available in case an anaphylaxis reaction occurs. This is the main reason why people should not get skin testing performed at corner stores or by people who have no medical training.[ citation needed ]
Antihistamines, which are commonly used to treat allergy symptoms, interfere with skin tests, as they can prevent the skin from reacting to the allergens being tested. People who take an antihistamine need either to choose a different form of allergy test or to stop taking the antihistamine temporarily before the test. The period of time needed can range from a day or two to 10 days or longer, depending on the specific medication. Some medications not primarily used as antihistamines, including tricyclic antidepressants, phenothiazine-based antipsychotics, and several kinds of medications used for gastrointestinal disorders, can similarly interfere with skin tests. [12]
People who have severe, generalized skin disease or an acute skin infection should not undergo skin testing, as one needs uninvolved skin for testing. Also, skin testing should be avoided for people at a heightened risk of anaphylactic shock, including people who are known to be highly sensitive to even the smallest amount of allergen. [13]
Besides skin tests, there are blood tests which measure a specific antibody in the blood. The IgE antibody plays a vital role in allergies but its levels in blood do not always correlate with the allergic reaction. [14]
There are many alternative health care practitioners who perform a variety of provocation neutralization tests, but the vast majority of these tests have no validity and have never been proven to work scientifically.
Allergies, also known as allergic diseases, are various conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis. Symptoms may include red eyes, an itchy rash, sneezing, coughing, a runny nose, shortness of breath, or swelling. Note that food intolerances and food poisoning are separate conditions.
An allergen is a type of antigen that produces an abnormally vigorous immune response in which the immune system fights off a perceived threat that would otherwise be harmless to the body. Such reactions are called allergies.
Anaphylaxis is a serious, potentially fatal allergic reaction and medical emergency that is rapid in onset and requires immediate medical attention regardless of use of emergency medication on site. It typically causes more than one of the following: an itchy rash, throat closing due to swelling that can obstruct or stop breathing; severe tongue swelling that can also interfere with or stop breathing; shortness of breath, vomiting, lightheadedness, loss of consciousness, low blood pressure, and medical shock. These symptoms typically start in minutes to hours and then increase very rapidly to life-threatening levels. Urgent medical treatment is required to prevent serious harm and death, even if the patient has used an epipen or has taken other medications in response, and even if symptoms appear to be improving.
Allergic rhinitis, of which the seasonal type is called hay fever, is a type of inflammation in the nose that occurs when the immune system overreacts to allergens in the air. Signs and symptoms include a runny or stuffy nose, sneezing, red, itchy, and watery eyes, and swelling around the eyes. The fluid from the nose is usually clear. Symptom onset is often within minutes following allergen exposure, and can affect sleep and the ability to work or study. Some people may develop symptoms only during specific times of the year, often as a result of pollen exposure. Many people with allergic rhinitis also have asthma, allergic conjunctivitis, or atopic dermatitis.
A food allergy is an abnormal immune response to food. The symptoms of the allergic reaction may range from mild to severe. They may include itchiness, swelling of the tongue, vomiting, diarrhea, hives, trouble breathing, or low blood pressure. This typically occurs within minutes to several hours of exposure. When the symptoms are severe, it is known as anaphylaxis. A food intolerance and food poisoning are separate conditions, not due to an immune response.
Contact dermatitis is a type of acute or chronic inflammation of the skin caused by exposure to chemical or physical agents. Symptoms of contact dermatitis can include itchy or dry skin, a red rash, bumps, blisters, or swelling. These rashes are not contagious or life-threatening, but can be very uncomfortable.
Hives, also known as urticaria, is a kind of skin rash with red, raised, itchy bumps. Hives may burn or sting. The patches of rash may appear on different body parts, with variable duration from minutes to days, and does not leave any long-lasting skin change. Fewer than 5% of cases last for more than six weeks. The condition frequently recurs.
Type I hypersensitivity, in the Gell and Coombs classification of allergic reactions, is an allergic reaction provoked by re-exposure to a specific type of antigen referred to as an allergen. Type I is distinct from type II, type III and type IV hypersensitivities. The relevance of the Gell and Coombs classification of allergic reactions has been questioned in the modern-day understanding of allergy, and it has limited utility in clinical practice.
Dermatographic urticaria is a skin disorder and one of the most common types of urticaria, affecting 2–5% of the population.
A patch test is a diagnostic method used to determine which specific substances cause allergic inflammation of a patient's skin.
Peanut allergy is a type of food allergy to peanuts. It is different from tree nut allergies, because peanuts are legumes and not true nuts. Physical symptoms of allergic reaction can include itchiness, hives, swelling, eczema, sneezing, asthma attack, abdominal pain, drop in blood pressure, diarrhea, and cardiac arrest. Anaphylaxis may occur. Those with a history of asthma are more likely to be severely affected.
Oral allergy syndrome (OAS) or pollen-food allergy is a type of food allergy classified by a cluster of allergic reactions in the mouth and throat in response to eating certain fruits, nuts, and vegetables. It typically develops in adults with hay fever.
Egg allergy is an immune hypersensitivity to proteins found in chicken eggs, and possibly goose, duck, or turkey eggs. Symptoms can be either rapid or gradual in onset. The latter can take hours to days to appear. The former may include anaphylaxis, a potentially life-threatening condition which requires treatment with epinephrine. Other presentations may include atopic dermatitis or inflammation of the esophagus.
A drug allergy is an allergy to a drug, most commonly a medication, and is a form of adverse drug reaction. Medical attention should be sought immediately if an allergic reaction is suspected.
An allergic response is a hypersensitive immune reaction to a substance that normally is harmless or would not cause an immune response in everyone. An allergic response may cause harmful symptoms such as itching or inflammation or tissue injury.
Allergy testing can help confirm or rule out allergies and consequently reduce adverse reactions and limit unnecessary avoidance and medications.
The Prausnitz–Küstner test is an immunologic test formerly used by physicians to determine if a patient has an allergic reaction to a specific antigen. The test has been replaced by the safer skin prick test. The PK test involves transferring serum from the test subject to another healthy person, essentially using the second person as a mixing vessel for antibodies and antigen. This is a pathway for transmission of blood-borne ailments like variant Creutzfeldt–Jakob disease, AIDS, and others, which is why the test is no longer recommended. Or in simple words, a test for the presence of immediate hypersensitivity in humans; test serum from an atopic individual is injected intradermally into a normal subject; the normal subject is challenged 24–48 hours later with the antigen suspected of causing the immediate hypersensitivity reaction in the atopic individual.
Allergies in children, an incidence which has increased over the last fifty years, are overreactions of the immune system often caused by foreign substances or genetics that may present themselves in different ways. There are multiple forms of testing, prevention, management, and treatment available if an allergy is present in a child. In some cases, it is possible for children to outgrow their allergies.
Fish allergy is an immune hypersensitivity to proteins found in fish. Symptoms can be either rapid or gradual in onset. The latter can take hours to days to appear. The former may include anaphylaxis, a potentially life-threatening condition which requires treatment with epinephrine. Other presentations may include atopic dermatitis or inflammation of the esophagus. Fish is one of the eight common food allergens which are responsible for 90% of allergic reactions to foods: cow's milk, eggs, wheat, shellfish, peanuts, tree nuts, fish, and soy beans.
A food allergy to sesame seeds has prevalence estimates in the range of 0.1–0.2% of the general population, and are higher in the Middle East and other countries where sesame seeds are used in traditional foods. Reporting of sesame seed allergy has increased in the 21st century, either due to a true increase from exposure to more sesame foods or due to an increase in awareness. Increasing sesame allergy rates have induced more countries to regulate food labels to identify sesame ingredients in products and the potential for allergy. In the United States, sesame became the ninth food allergen with mandatory labeling, effective 1 January 2023.
