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Diagnosing a Food Allergy | Allergy Shmallergy


Anyone can develop a food allergy at any age to any food.

So when someone experience symptoms of an allergic reaction after eating, it is CRITICAL that they see a doctor to explore the possibility of a food allergy.

Symptoms of a food allergy vary not only from person to person, but from reaction to reaction. Some reactions are mild, while others (even to the same allergen) can be very severe.

When someone makes an appointment with a healthcare provider to discuss a reaction, there are several ways their doctor may go about diagnosing a food allergy. First, doctors will take a detailed medical history. It helps to bring a food journal of everything you have eaten prior to a reaction for the doctor to review. Only one test definitively determines a food allergy (the Oral Food Challenge). All others offer a picture of how the body is reacting to food and the likelihood it will experience severe symptoms after ingesting that food again.

Oral Food Challenge

This test is considered the gold standard for diagnosing food allergies. This test measures how much of an allergen a patient can tolerate without reacting. If a patient can ingest a certain challenge level of allergen without reacting, they are considered not allergic to that allergen. During an oral food challenge, a patient is giving an increasing amount of an allergen beginning with the smallest dose. Oral food challenges are ONLY performed in a medically supervised setting where healthcare professionals monitor the patient for signs of an allergic reaction. These tests last several hours – so come prepared with books, devices, toys, etc.

Oral food challenges are also used to test whether a patient has outgrown a particular allergy. [See What is an Oral Food Challenge and How to Prepare for additional information.]

Blood Test

Blood tests measure a specific antibody in the blood called IgE. IgE, or immunoglobulin E, is the antibody that causes your immune system to react abnormally to certain food resulting in food allergy. A doctor will take a blood sample and test it against certain allergens. This gives the doctor a picture of how the body is responding to that food. There are also related blood tests called component tests. These helps narrow down true allergies (which can cause reactions) to false positives (or allergies to harmless protein in food). A patient can typically expect results in several days to weeks and will need to discuss the results with their doctor. The results of a blood test DO NOT PREDICT SEVERITY of a food allergy – they only predict the probability of a food allergy.

Skin Testing

Skin testing or skin prick tests are an in-office procedure that can provide results in 15-30 minutes. During this test, a small amount of allergen is applied to the skin (typically on a patients forearm or back). If a wheal (much like a bug bite) appears, the site is measured and considered positive. This relatively short test is not painful, but can be itchy or uncomfortable.

Blood and skin tests sometimes yield false positive results for a variety of reasons. Therefore, it is important you work with an allergist trained at interpreting the results and offering practical guidance for next steps.

Food Elimination Diet

Food elimination diets are just as their names suggest: a strict diet to be followed that does not contain a certain allergen (or several allergens), generally for up to four weeks. Following the elimination period of the diet, allergens are gradually added back in one by one to identify which one(s) a patient is reacting to. It helps to keep a food journal during this process to record what you eat and identify any other reactions you might have. This process can be tricky at first as most people are not well-practiced in reading ingredient lists and eliminating allergens when they hide in tricky places.

It is CRITICAL to see a doctor when you suspect you have a food allergy. Studies show that the difference between a food allergy and a food intolerance isn’t well understood by most patients. That difference can be crucial: A patient does not want to take on the tremendous stress and burden of avoiding a food unnecessarily. Nor do patients want to be caught having a severe reaction without life-saving epinephrine and a plan of action.

Under the supervision of a trained medical professional, diagnosing (or ruling out!) a food allergy can be done simply and send you on your way to better health quickly.

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