Food allergies – The often long path to diagnosis

Food allergies can only be diagnosed by a doctor and the path to diagnosing a food allergy can be complicated. It begins with a patient recounting their medical history. The physician will ask for relevant information, such as what symptoms of a food allergy have occurred for the first time, and whether other family members suffer from allergies. A diary of the foods consumed and symptoms experienced by the patient can be helpful.

Additional steps to diagnosing food allergies

Blood and / or skin tests are the next steps. In the blood of a food-allergy sufferer, the number of certain antibodies is elevated. This so-called specific IgE antibody value can be determined very well. However, a blood test alone does not provide a reliable result. Only through the results of the blood tests (i.e. the IgE antibodies) and the patient's data on symptoms and the intake of certain foodstuffs can a food allergy be diagnosed or ruled out.

The standard skin test for food allergies is the prick test

For the prick test, the allergist marks spots on the skin on the inside of the forearm. There, he places a drop of solutions containing the allergens to be tested. Then, the allergist sticks through the liquid into the skin, which absorbs the allergens. Under the surface, the allergens are in contact with so-called mast cells. If an allergy is present, the mast cells emit messenger substances such as histamine, causing the skin to redden, the tissue fluid to eventually blow out, the skin to swell and a wheal (hives) to occur, and the patient to experience some itching.

False positives from the prick test

Test reactions can only provide clues and do not reflect the true extent of an allergy. Drugs such as antihistamines, sleeping pills or cortisone can dampen the reaction. Irritated skin, on the other hand, can cause a particularly strong test result even if the allergic reaction is only weak in everyday life. In addition, fever, infections, and alcohol consumption can falsify test results.

This testing is further complicated by the fact that a prick test does not exist for all food allergens. If, for example, a pepper allergy is suspected, no such testing liquid is available. In this case, the allergist could carry out a prick-to-prick test. He first pricks the food which is suspected of triggering the allergy (for example, into a pepper) and then into the skin of the patient.

Only half of all positive test results match the symptoms

As with the positive blood test, a food allergy is only present when the test results match the patient's symptoms. As a rule of thumb, the medical guideline for food allergies states that only half of all positive test results on allergies really come with symptoms.

The next step for diagnosing a food allergy: diet

If blood and skin tests are positive, the next step can be a diagnostic diet. This is selected according to the test results. If there is a reasonable suspicion of individual allergy triggers - such as chicken eggs or soy - the diet will consist of removing these allergens from the diet. For a certain period of time, the patient has to abstain from these foods completely.

After four weeks at the latest, the patient’s symptoms should improve significantly. If the improvement fails to materialize, there is probably no connection between the symptoms and the particular food. Then there is no reason to stick to the diet.

When a provocation test is useful - and when it isn’t

If, however, the dietary change leads to an improvement, the doctor and the patient decide whether a provocation test is necessary to confirm the diagnosis. The potentially allergen is administered and an allergic reaction is maintained. Only the provocation can confirm or exclude the connection between symptoms and nutrition with certainty. In individual cases - if the results so far are clear - the doctor and the patient can also decide against a provocation test.

Please see also:

Food allergies and their symptoms

Causes of food allergies

Preventing food allergies

Therapy for food allergies