Skin testing on the arm is a common way for detecting an allergy, but it is not as effective as other tests. Patch test Diagnosis is usually based on a medical history, elimination diet, skin prick test, blood tests for<unk> -specific IgE antibodies, or oral<unk>  challenge. * For skin-prick tests, a tiny board with protruding needles is used. The allergens are placed either on the board or directly on the skin. The board is then placed on the skin, to puncture the skin and for the allergens to enter the body. If a hive appears, the person is considered positive for the allergy. This test only works for IgE antibodies. Allergic reactions caused by other antibodies cannot be detected through skin-prick tests. Skin-prick testing is easy to do and results are available in minutes. Different allergists may use different devices for testing. Some use a "bifurcated needle", which looks like a fork with two prongs. Others use a "multitest", which may look like a small board with several pins sticking out of it. In these tests, a tiny amount of the suspected allergen is put onto the skin or into a testing device, and the device is placed on the skin to prick, or break through, the top layer of skin. This puts a small amount of the allergen under the skin. A hive will form at any spot where the person is allergic. This test generally yields a positive or negative result. It is good for quickly learning if a person is allergic to a particular<unk>  or not because it detects IgE. Skin tests cannot predict if a reaction would occur or what kind of reaction might occur if a person ingests that particular allergen. They can, however, confirm an allergy in light of a patient's history of reactions to a particular<unk> . Non-IgE-mediated allergies cannot be detected by this method. * Patch testing is used to determine if a specific substance causes allergic inflammation of the skin. It tests for delayed<unk>  reactions. * Blood testing is another way to test for allergies; however, it poses the same disadvantage and only detects IgE allergens and does not work for every possible allergen. Radioallergosorbent testing (RAST) is used to detect IgE antibodies present to a certain allergen. The score taken from the RAST is compared to predictive values, taken from a specific type of RAST. If the score is higher than the predictive values, a great chance the allergy is present in the person exists. One advantage of this test is that it can test many allergens at one time. A CAP-RAST has greater specificity than RAST; it can show the amount of IgE present to each allergen. Researchers have been able to determine "predictive values" for certain<unk> s, which can be compared to the RAST results. If a person's RAST score is higher than the predictive value for that<unk> , over a 95% chance exists that patients will have an allergic reaction (limited to rash and anaphylaxis reactions) if they ingest that<unk> . Currently, predictive values are available for milk, egg, peanut, fish, soy, and wheat. Blood tests allow for hundreds of allergens to be screened from a single sample, and cover<unk> es as well as inhalants. However, non-IgE-mediated allergies cannot be detected by this method. Other widely promoted tests such as the antigen leukocyte cellular antibody test and the<unk>  profile are considered unproven methods, the use of which is not advised. *<unk>  challenges test for allergens other than those caused by IgE allergens. The allergen is given to the person in the form of a pill, so the person can ingest the allergen directly. The person is watched for signs and symptoms. The problem with<unk>  challenges is that they must be performed in the hospital under careful watch, due to the possibility of anaphylaxis.<unk>  challenges, especially double-blind, placebo-controlled<unk>  challenges, are the gold standard for diagnosis of<unk> es, including most non-IgE-mediated reactions, but is rarely done. Blind<unk>  challenges involve packaging the suspected allergen into a capsule, giving it to the patient, and observing the patient for signs or symptoms of an allergic reaction. The recommended method for diagnosing<unk>  is to be assessed by an allergist. The allergist will review the patient's history and the symptoms or reactions that have been noted after<unk>  ingestion. If the allergist feels the symptoms or reactions are consistent with<unk> , he/she will perform allergy tests. Additional diagnostic tools for evaluation of eosinophilic or non-IgE mediated reactions include endoscopy, colonoscopy, and biopsy. Differential diagnosis Important differential diagnoses are: * Lactose intolerance generally develops later in life, but can present in young patients in severe cases. It is not an immune reaction and is due to an enzyme deficiency (lactase). It is more common in many non-Western people. * Celiac disease. While it is caused by a permanent intolerance to gluten (present in wheat, rye, barley and oats), is not an allergy nor simply an intolerance, but a chronic, multiple-organ autoimmune disorder primarily affecting the small intestine. * Irritable bowel syndrome * C1 Esterase inhibitor deficiency (hereditary angioedema), a rare disease, generally causes attacks of angioedema, but can present solely with abdominal pain and occasional diarrhea, and thus may be confused with allergy-triggered angioedema.
Food allergy
Coeliac disease
Metal allergy
Foodborne illness
Nickel allergy
Food intolerance
Poultry allergy
Sesame allergy