When diagnosing a food allergy, 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.
Food Allergy Reactions
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.
Testing for a Food Allergy
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.
Other 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 professionally 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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