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 patients history of reactions to a particular food. 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 food 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 foods, which can be compared to the RAST results. If a persons RAST score is higher than the predictive value for that food, over a 95% chance exists that patients will have an allergic reaction (limited to rash and anaphylaxis reactions) if they ingest that food. Currently, predictive values are available for milk, egg, peanut, fish, soy, and wheat.
Some types of food allergies among children resolve with age, including that to milk, eggs, and soy; while others such as to nuts and shellfish typically do not.In the developed world, about 4% to 8% of people have at least one food allergy. They are more common in children than adults and appear to be increasing in frequency. Male children appear to be more commonly affected than females. Some allergies more commonly develop early in life, while others typically develop in later life. In developed countries, more people believe they have food allergies when they actually do not have them. Signs and symptoms
Food allergy symptoms occur within minutes to hours after exposure and may include:
Rash
Hives
Itching of mouth, lips, tongue, throat, eyes, skin, or other areas
Swelling (angioedema) of lips, tongue, eyelids, or the whole face
Difficulty swallowing
Runny or congested nose
Hoarse voice
Wheezing and/or shortness of breath
Diarrhea, abdominal pain, and/or stomach cramps
Lightheadedness
Fainting
Nausea
VomitingIn some cases, however, onset of symptoms may be delayed for hours.Symptoms can vary. The amount of food needed to trigger a reaction also varies.Serious danger regarding allergies can begin when the respiratory tract or blood circulation is affected. The former can be indicated through wheezing and cyanosis. Poor blood circulation leads to a weak pulse, pale skin and fainting.A severe case of an allergic reaction, caused by symptoms affecting the respiratory tract and blood circulation, is called anaphylaxis. When symptoms are related to a drop in blood pressure, the person is said to be in anaphylactic shock.