Taking a good history is very helpful to determine if a person has a food allergy. Food allergy reactions that are life threatening will generally begin within minutes, but may present in a delayed fashion up to 90 minutes after eating the suspected food. A person who complains of a food allergy 12 hours after eating is most likely not describing a true food allergy.
A reaction can vary from itchy skin, hives or welts, lip swelling, throat and tongue swelling, vomiting, upset stomach, chest tightness and wheezing. Non-allergic food hypersensitivities can occur if you eat a food and suffer from a headache or flushing. These reactions are always less than what is seen for a food allergy. Many people complain of an upset stomach or diarrhea when in reality these foods may not agree with you and are not a food allergy. Seeing an allergist is very important, since an allergist is trained to diagnose food allergies and is well versed on treating food allergic reactions.
Skin testing with the offending food is the most common way to test for a food allergy. The doctor can do a skin test. The doctor will prick your skin with the suspected food and observe to see if a skin reaction appears. He or she may use fresh food or a prepared serum containing the food. At times a RAST for Immunoglobulin E (radio immunoassay test using a blood sample) will be ordered. This is a blood test measuring the antibody immunoglobulin E for the suspected food. This test costs more than skin testing, but can give the doctor a numerical value that can be followed from time to time, to see if the numbers are increasing or decreasing.
At times, a food challenge will de done. This may be blinded (the patient does not know what they are eating) or open (the patient is aware of what the food is). A food challenge should only be done by someone trained in this procedure and by someone with the ability to treat an anaphylactic (life threatening reaction). A food challenge is sometimes done to see if a person has definitely outgrown or lost their food allergy. If a reaction is going to occur, it will first occur in a controlled setting.
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