Methods of Clinical Allergy Testing

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A substance which can trigger an allergic reaction is known as an allergen. To determine the specific substances that are triggering the allergies, your immunologist/allergist will effectively and safely test your skin, or occasionally your blood, using small amounts of the commonly troublesome allergens like pollen. Generally, skin testing is a more valuable and valid tool for testing of allergies to environmental allergens than blood tests.

The symptoms of allergy can include:

  • Respiratory symptoms: itchy eyes, throat or nose; watery eyes, runny nose, nasal congestion, wheezing or chest congestion.
  • Skin symptoms: hives, atopic dermatitis (eczema) or generalized itchiness
  • Other symptoms: stinging insect allergic reactions other than the large swelling at the site of the sting, anaphylaxis, abdominal symptoms (diarrhea, cramping) after eating certain foods.

 

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All of the following are common allergens:

  • Products from dust mites which live in homes
  • Proteins from furry pets that are found in their saliva, skin secretions and urine.
  • Molds in the air or in houses
  • Tree, weed and grass pollen; or/and cockroach droppings
  • Venoms from stinging insects
  • Foods
  • Natural rubber latex, like balloons and gloves
  • Drugs, like as penicillin

Methods Of Clinical Allergy Testing

1. Skin prick test

The method involves the delivery of a tiny amount of purified extracts of allergenic substances into the skin (normally on the arms or back) using a sterile pricking device. If you`ve an allergy, the specific allergens which you`re allergic to will cause a reaction to start in your body. To protect your body from allergen or the perceived threat, the immune system of an allergic individual produces antibodies known as IgE (immunoglobulin E).

Immunoglobulin E antibodies are found in the skin, mucous membranes, and lungs. They cause the mast cells (a kind of cell that is involved in the immune response of the body) to release chemicals, such as histamine, into the bloodstream. It`s these chemicals which bring on most of the symptoms of allergy which affect a person’s lungs, eyes, gastrointestinal tract, nose, throat or skin.

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Histamine is responsible for the localized swelling that`s observed at the spots where small amounts of allergens were introduced. Because Immunoglobulin E antibodies are unique to every allergen, checking for the specific variants in the blood can help determining if an allergy is present. For instance, if one is allergic to wasps but not to mites, the spot where the wasp allergen touched their skin will itch and swell, forming a small dime-sized hive and the spot where the mite allergen touched their skin will remain normal.

The results of the test are available within around twenty minutes of testing, hence you do not have to wait for a long time to know what`s triggering your allergies. In addition to that, apart from the slightly swollen, tiny hives where the prick test was performed, you will not have any other symptoms. The swelling goes away within around thirty minutes.

It`s important that patients undergoing the allergy skin testing should not use any antihistamine medications for a few days before testing because these medications will interfere with the test responses.

It`s important to note that a positive allergy skin prick test doesn`t mean that a certain substance will cause allergic symptoms. Many individuals can have positive skin-prick test reactions without any allergy symptoms. That`s why it`s important that the allergy tests be performed by a certified allergist who has obtained a detailed medical history of the patient so that they can correlate the clinical history of the patient with positive test results.

2. Intradermal test

Involves using a syringe to inject a tiny amount of the allergen under your skin. This method of testing is more sensitive than the prick- skin test technique, hence it is used if all the prick-skin tests are negative.

3. Skin patch test

For a skin patch test, an allergen solution is placed on a pad which is taped to the skin for 24 – 72 hours. It`s used to detect a skin allergy known as contact dermatitis.

4. Oral food challenge

For medication allergy testing or food allergy testing an oral food challenge, also known as a challenge test, can be considered. This should only be considered by an experienced allergist/immunologist. The advantage of performing a challenge test is that it can certainly disprove allergy.

5. Blood tests

Blood tests, often known as CAP-RAST, RAST, measure the amount of immunoglobulin E levels in the blood. In the blood test, a nurse or doctor can request either the total amount of IgE in the blood or only specify the allergens they suspect might be triggering the symptoms, such as dog, cat, house dust mites, or from a wide-range of allergens, including grasses, foods, tree pollen, fungi or moulds.

With the result of the test, the physician can confirm the relative allergic sensitivity levels to the various suspected triggers, and, in conjunction with an examination and clinical history, tailor treatments and advice on the avoidance techniques which can be used to improve symptoms. If the results of the blood test are negative and the symptoms persist, further investigations might be required.

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