Food Allergy Symptoms and Diagnosis
Most food allergy symptoms are mild, but in the United States there are approximately 30,000 episodes of food-induced life-threatening anaphylaxis, associated with 150 to 200 deaths annually. Symptoms usually appear within minutes of eating the food, though they can sometimes occur hours later.
Common symptoms include
a tingling sensation in the mouth
skin problems such as generalized hives or itching and flushing
stomach discomfort such as abdominal cramps; diarrhea, or vomiting
swelling of the tongue and throat
a drop in blood pressure, dizziness or loss of consciousness
Diagnosing Food Allergy
Studies show that more than half of presumed food allergies are not actually allergies.
It takes more than a couple of tests to know for sure. Board-certified allergists have special training and experience in putting together all the pieces of your personal history, your medical history and physical exams to come up with a diagnosis. In addition, we now have Guidelines for the Diagnosis and Management of Food Allergy in the U.S. (National Institutes for Allergy and Infectious Diseases, December 2010) that provide in-depth information on what works and doesn’t work when it comes to food allergy.
The first thing a doctor looks at when diagnosing food allergy is your history of symptoms. If you think you might have a food allergy, keep a written diary with the following information:
What symptoms did you notice?
How long after eating did you notice symptoms?
How long did the symptoms last and how severe were they?
Did you do anything to help ease the symptoms (such as take prescription or over-the-counter medications)?
What exactly did you eat and how much?
Where and how was the food processed? Was it at home? A restaurant?
How was the food prepared: raw? boiled? roasted?
Were you doing anything else during or just after your meal, like exercising?
Show your diary to your health care provider. Sometimes the food allergy is obvious, but follow-up testing is important to confirm the diagnosis.
Food Allergy Testing
The food allergy tests performed most often by allergists are skin prick tests. A diluted extract of the food is placed on your skin, then the skin is scratched with a needle. If you develop a raised skin reaction (called a wheal) at the place of the needle prick, that indicates possible allergy. If there is no reaction, you are unlikely to be allergic to the food.
Skin prick tests are quite accurate for foods with stable proteins, including peanut, milk, egg, tree nuts, fish and shellfish – some of the most common food allergens in the United States. They are less reliable for fruits and vegetables, which have proteins that break down quickly.
Blood tests that look for IgE antibodies (Immunoglobulin E, particles in the blood that indicate allergy) are also useful for identifying food allergies. They are particularly helpful for people whose allergy history puts them at high risk of serious reaction to a skin prick test; whose skin problems make skin-prick uncomfortable or dangerous; or who take certain medications that interfere with skin prick test results.
No test is perfect. A positive skin or blood test response does not necessarily mean you would have an allergic reaction from eating the food.
Food allergy guidelines say the diagnostic tests to evaluate food allergy should be based on the patient’s medical history and not be comprised of general large panels of food allergens. Patients who test allergic to numerous foods might choose to eat very restrictive diets, which can be unhealthy and difficult to follow. That’s why seeing an allergist trained to put all the evidence together for a diagnosis is important.
When tests are inconclusive, NIH Food Allergy Guidelines recommend your allergist may use an oral food challenge. Because this test always carries a risk, it must be performed by a health care provider trained in how to conduct this test and at a medical facility that has appropriate medicines and devices to treat potentially severe allergic reactions.
Treatment — Be Prepared
If you or your child has been diagnosed with a food allergy, talk with your health care provider about how to avoid reactions. Ask for a written Anaphylaxis Emergency Action Plan. For children with food allergies, give a copy of the action plan to the school and all caregivers.
Early recognition and treatment of symptoms is critical.
Most often, you will need to completely avoid eating the food you are allergic to. If you have a life-threatening food allergy, your health care provider will prescribe epinephrine auto-injectors to use in anaphylactic emergency situations. Be sure you carry two auto-injectors with you at all times and know how to use them. Make sure school, family, friends and other caregivers are also trained on how and when to use epinephrine. Consider wearing a medical alert bracelet that lists foods you are allergic to and has instructions to give you epinephrine if you are unable to do so yourself.
For more information on anaphylaxis causes, treatment and prevention, order a free copy of Allergy & Asthma Network’s Understanding Anaphylaxis: How to prevent, treat and manage life-threatening allergies.