Allergy testing, Scientific article

Methods of allergy and food intolerance testing

There is no fix-all cure for allergies and food intolerances. Therefore, it is important for allergy sufferers to take an allergy test to determine the allergens that are triggering their reactions. The most common allergen sources causing allergy patients trouble are grasses, trees and weeds, mold, dust mites, animal fur and dander, insect venom, certain foods, and drugs. The most common food groups causing adverse reactions are eggs, cow’s milk, soy, wheat, peanuts, tree nuts, fish and shellfish.  

Allergy and food intolerance testing  

Allergists usually test their patients with a skin test or a blood test. The third method to test out food intolerances is the so-called elimination diet.

Skin tests

There are three different types of skin tests, which allergists either perform standalone or in combination with each other. These three types are prick tests, intradermal tests, and patch tests. Results are usually available promptly, as the skin will react within 20 or 30 minutes after application. 

Prick tests

skin prick tests
Typically, doctors will start with a prick test. For this test, the doctor places an allergen in a liquid. Then, they place this liquid on the patient’s skin and puncture it with a special tool. The doctor will closely monitor how the skin reacts to the allergen. If redness, swelling, or itchiness occur, the allergist marks the patient counts as allergic to this specific allergen.  

Skin scratch tests

If prick test results are not clear, the allergist will often perform a skin scratch test. For the scratch test, they remove a small area of skin and rub the allergen over this spot. This way, the allergen can reach deeper levels of tissue compared to the prick test and might achieve a stronger reaction. 

Intradermal skin test

If the prick test is not conclusive, sometimes an intradermal skin test is the second step. For this test, the allergist injects a tiny amount of the allergen into the dermis layer (thickest layer) of the patient’s skin and monitors the reaction.

Patch test

Lastly, another skin testing option is the patch test. For this test, the allergist places adhesive patches with different allergens on the patient’s skin. These patches remain on the body of the patient over the course of four days. After 48, 72 and 96 hours after the initial application, the allergist reviews the reactions. 

All forms of skin tests can cause relative discomfort for the patient. Positive reactions to an allergen will cause itchy red bumps on the skin, but they look and feel very similar to mosquito bites and fade in a matter of minutes to hours. In some cases, allergists may apply soothing creams to the skin or have patients take an antihistamine to decrease the reaction. 

Blood tests

blood allergy test
Blood tests screen for IgE antibodies in a patient’s blood that are specific to a certain allergen or food. The higher the level of IgE, the more likely it is that a particular substance will cause an allergic reaction. Similarly, food intolerances are measured by the levels of IgG antibodies specific to a certain food antigen in a patient’s blood.

As opposed to skin tests, it will take several days to receive the result of a blood test. Blood tests are usually done at a lab instead of a doctor’s office. The blood sample will undergo a complicated process of analysis before the results can be confirmed. Despite the longer waiting time for the results, allergists consider blood tests as the safer option. There is no risk of triggering a severe allergic reaction during the blood test process. Especially for patients with a high risk for a life-threatening anaphylactic reaction, as well as for patients with heart disease or asthma, blood testing is the best option.   

Allergy blood tests are also used for patients continuously taking medicine without break that could possibly interfere with skin testing, as well as patients suffering from severe skin conditions such as eczema or psoriasis.  

RAST and ELISA tests

The go-to blood test to diagnose allergies used to be the so-called RAST (radioimmunoassay) test.  

Over the past thirty years, we made a lot of progress in the field of blood allergy testing. New methods such as in vitro molecular allergy diagnostics have been developed. 

7DROPS is an ELISA (enzyme-linked immunosorbent assay) based in vitro multiplex allergy test, which allows the simultaneous measurement of total IgE and specific IgE against a plethora of allergen extracts and molecular allergens. In simple words: it is a very comprehensive allergy test that tests up to 300 allergens and 286 food antigens from only 100 µl of serum or plasma. 

Provocation tests

In case both skin and blood tests fail to provide conclusive results, provocation tests can be useful. For this method, patients ingest very small amounts of a potentially triggering substance, while the allergist observes for any physical reaction. There are three types of provocation tests: oral, nasal, and inhalation tests.  

Oral provocation test

The oral provocation test concerns itself with foods that may cause an allergic reaction. This type of test typically requires a hospital stay, since it requires a safe environment and observation by a specifically trained healthcare professional. Patients are given foods to eat while their physical reaction is monitored. The oral provocation test is useful in two ways. It assesses foods that cause an allergic reaction and need to be avoided, and determines foods that do not cause any symptoms and can be enjoyed without concern. 

Nasal provocation test

The nasal provocation test can test for pollen allergy. For this test, the allergist applies an allergen such as birch pollen to the nasal mucous membrane of the patient. Patients suffering from hay fever will experience nasal irritation, reduced nasal inspiratory flow, and/or increased mucous production.  

Inhalation provocation test

For the inhalation provocation test, the bronchial mucosa is exposed to suspected allergens (e.g., pollen) through inhalation. The confirm the presence of an allergy, the allergist measures the effect on the patient’s breathing ability through pulmonary function testing.

Elimination diet

Like the name suggests, the elimination diet is a specific eating plan that omits certain foods or food groups from a person’s diet. These foods can potentially cause an adverse food reaction – a food intolerance. The patient removes certain foods from their diet for a certain time period and later reintroduces them to the system step by step. During this reintroduction phase, the patient looks out for symptoms in the body that show a reaction. Usually, it will take only 5 to 6 weeks to identify food intolerances.  

In the next phase, the patient reintroduces food groups are to the system individually over two to three days. Meanwhile, the patient is looking out for symptoms. These symptoms could be rashes and skin changes, joint pain, headaches or migraines, fatigue, difficulty sleeping, changes in breathing, bloating, stomach pain or cramps and changes in bowel habits.  

Patients suspecting a food allergy should only do an elimination diet under the supervision of a medical professional. Reintroducing a suspected food allergen may trigger dangerous allergic conditions such as anaphylaxis.

Steps after allergy testing

No matter which method of allergy testing is used, patients should consult their GP or allergy specialist to discuss results. Once they know what allergens are causing their symptoms, the patient has to learn to avoid them to improve their general health and quality of life.  

Therapy may include medication (antihistamines and corticosteroids in the form of pills and sprays) to ease symptoms, as well as allergen-specific-immunotherapy (AIT). AIT trains a patient’s immune system to tolerate the culprit allergen (e.g., grass pollen).  

Sources: ecarf.orgncbi.nlm.nih.gov

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