Skin Prick Tests Reveal Food Allergies Better than Commercial Allergens


15. 01. 2018

Food intolerance is often incorrectly labeled or referred to as an allergy. In reality however, only a very small fraction of these reactions are caused by true, immunologically induced allergies. Often, the significance of food intolerance is exaggerated. In many cases however, a true and potentially dangerous allergy is not properly identified or discovered with considerable delay.

The diagnosis of food allergies is determined on the basis of clinical symptoms and the results of accompanying detailed examinations. Whether the allergy is confirmed or ruled out often has considerable effect on the quality of the patient's life. Canadian Medical's allergists try to prevent unnecessary food elimination diets as these can sometimes even lead to endangering the health state of a patient.

The first step in the diagnostic process is a thorough interview with the patient or the parents of the child. Our specialists need to understand the reactions and circumstances which occurred prior to the reaction taking place. They need to identify the symptoms, its severity and understand what the interval was between the consumption of the food and the onset of the symptoms. They need to understand whether the food was consumed raw, cooked or prepared otherwise. A very important piece of information is whether the patient suffers from any other allergies, mainly allergens such as pollen, mites, latex etc.

Food allergies are usually carried out using skin prick tests to determine the presence of specific IgE antibodies in the serum. Positive results from these tests prove the presence of IgE specific antibodies to food. However, these results alone are not sufficient. The positive results only prove that the patient is more sensitive, yet the sensitivity may not result in any manifestations. In fact, patients that are exposed to the allergen may not experience any symptoms and have tolerance to the food throughout their entire life. On the other hand some patients may suffer from allergies from childhood, but then become used to the allergen and no longer suffer from reactions to it. However, their skin prick tests would continue revealing increased sensitivity to the particular agent.

The most effective way of confirming or ruling out a diagnosis is by introducing a provocative test with the actual food under medical supervision. The goal of this is to induce the symptoms connected with consuming the particular food. These particular tests are done and evaluated in line with international recommendations and criteria.

Skin prick tests

Prior to running the skin prick test, it is necessary to stop taking antihistamines for at least a week. These tests are entirely safe. In fact, there is no age limit and it can be used on infants as well. The test itself is carried out either on the forearm or on the back. Droplets of an allergen solution are applied and then, these are pierced gently with a lancet which looks like a plastic pin with a very thin tip. After 15 minutes have passed, the various degrees of reaction are evaluated. If the individual has a higher level of antibodies to specific allergens, then the reaction is visible in the form of raised irritation surrounded by redness. This could be best compared to what a mosquito bite looks like.  The reaction to the test (if any), disappears within two hours.

The test also checks for the most common airborne allergens such as mites, mold, animal allergens and pollen from trees, grasses and weeds. For these tests, an extract produced by pharmaceutical companies is administered to the patient.

Skin prick tests with fresh food

In the case of foods, the use of commercially available allergen extracts is highly problematic. For foods, there is currently no coherent and unified extract type with equal amounts of allergens and the same biological activity. Allergens of many foods are unstable in nature, particularly in the case of fruits and vegetables. During the processing needed to prepare them for test solutions, they are often destroyed and as a result the test may show a false negative. Many studies have proven that fresh food tests are more appropriate than available commercial allergens.

For several years already, it is not uncommon abroad for the skin prick tests to use native food, i.e. fresh food. Only this method truly ensures that all of the allergy-causing agents are present in the particular food and that those agents have show sufficient biological activity.

There is no standard list of foods. The allergist determines a list of suspected foods based on the analysis of the patient's complications and his or her dietary habits. It is also important to consider cross-reactions of pollen and food but also any hidden allergens. The suspect foods are then brought to the next visit and must be fresh and in their native state. Usually, a range of classic basic foods is tested including eggs, milk, peanuts, nuts, soy, poppy seed, sesame, cereal flour, poultry, red meat, fish, peach, apple, carrots, potatoes and celery.

From each food type, a drop is applied to the skin, which is then pierced by a lancet. The reaction is then observed after a 15 minute period has passed. The drop is pressed directly out of the fruit which is fresh. The same can be done with milk, egg white, egg yolk etc. Dried foods (such as nuts, seeds and cereal grains) first need to be grated, crushed, dissolved and mixed in a saline solution to create a paste. The resulting paste is then applied onto the skin and yet again, pierced with the lancet.

After the tests have been administered, the doctor is able to identify which foods need to be further examined using blood samples to confirm the diagnosis. The results of the test and a person's reaction to foods can change during one's lifetime. This is why (especially during childhood), skin prick tests and provocative food tests are repeated with 6, 12, 18 or 24 month intervals.

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