Symptoms of a food allergy vary significantly from person to person, as does the amount of food needed to trigger an allergic reaction. While most food-related symptoms occur within two hours of ingestion, in some rare cases, the reaction may be delayed by four to six hours or even longer. Common symptoms of a food-related allergic reaction include: digestive problems, hives or swollen airways. The most severe allergic reactions may result in anaphylaxis, which can impair breathing, cause a dramatic drop in blood pressure, and affect heart rate to a fatal degree.
Some patients may experience an itching and/or tingling feeling in their mouths after consuming certain fruits, which is referred to as pollen-food allergy syndrome or oral allergy syndrome. For example, patients allergic to birch pollen can have this reaction when eating an apple. In rare cases, pollen-food allergy syndrome can lead to anaphylaxis.
The diagnosis of a food allergy generally requires a thorough medical history of the patient including what and how much you ate, how long it took for symptoms to develop, what symptoms you experienced and how long it lasted. Your doctor may order skin and/or blood tests in making a diagnosis. However,a “positive” result on any one test is not an absolute indication of a food allergy. Allergists rely on their experience to properly interpret the results of tests within the overall context of the patient’s medical history and properly diagnose a food allergy. If you suspect you have a food allergy, talk to your Allergy Partners physician to determine what method of diagnosis is most suitable.
In this test, a tiny amount of liquid containing suspected food is placed on the skin of your arms or back. The skin is then pricked with a small sterile probe, allowing the liquid to seep under the skin. After about 20 minutes, a hive (a bump similar to a mosquito bite) may form and will be compared to the bump at the site of the control, where a liquid not containing any allergen is placed.
A blood test (commonly known as RAST or ImmunoCAP) detects the presence of allergen-specific antibodies known as immunoglobulin E (IgE) antibodies.Additionally, a relatively new test, called a “component test” can be ordered to gain more specific information and is mostly used for peanut allergies. Blood tests have been used extensively but often are not specifically based on patients’ detailed diet diary. When not properly utilized, the results of a blood test can be very confusing and may lead to unnecessary food restriction. Allergy Partners allergists use their experience to determine when a blood test may be helpful and to properly interpret the results of the blood test.
There are a number of non-standardized tests that are advertised as helping diagnose food allergy. These tests include allergen-specific IgG blood tests, antigen leukocyte cellular antibody tests, hair analysis, and applied kinesiology. Their use in the diagnosis of food allergy is not advised.
Oral Food Challenge
In an oral food challenge, small increment amounts of food are fed to the patient over a period of a few hours to determine if a reaction occurs. Due to the possibility of a severe reaction, it must be conducted under medical supervision by an experienced doctor and in a facility with emergency medication and equipment on hand. The gold standard for a food challenge is one that is double-blind and placebo-controlled, though it may still have very good diagnostic value when lacking these conditions.
Food allergies can be challenging and stressful, so knowing what you or your child is eating is an important first step. If you have doubts about a possible food allergy, err on the side of caution until you have a chance to speak with an Allergy Partners physician.