Skin Testing
Skin Prick Testing
Skin prick testing is an important part of the diagnosis of an allergy. This quick and relatively pain free test is used for the specific diagnosis of the patient's allergy.
When a new patient first meets the clinician who will be managing their allergy treatment a case history should be taken. This comes in the form of a simple questionnaire that answers some of clinician questions about the patient's allergy symptoms, such as 'At what times of year does the allergy occur' 'Does the patient keep any pets?' From the answers to these simple questions it is possible to propose that the patient is allergic to tree pollen (spring hay-fever) or grass pollen (summer hay-fever) or the dust mites that live in everybody's home. If the patient keeps pets and suffers all year round allergy then their dog or cat may be the cause of their symptoms. From the case history the clinician is able to work out if a skin prick test is necessary and if testing is needed, just what allergies to test for. In some cases, such as when a patient has atopic dermatitis or has been taking antihistamines, the clinician may decide to take a small blood sample for testing instead of carrying out a skin prick test. This blood sample will then be sent away to a laboratory that uses techniques like RAST testing to determine the patient's allergies. The disadvantage of this technique is that it may take several weeks for the results to arrive while with skin prick testing the results are known on the day the test is carried out.
What Happens During a Skin Prick Test.
1. The skin prick test starts with the clinician putting a small drop of each allergen extract on the skin of the patient. Usually the allergen extracts are placed on the forearm though in children the back is sometimes used. A separate drop of allergen extract is administered for each allergen source being tested; also separate drops of the positive and negative control solutions are required. In this way a large number of different allergies can be tested at once.
2. Once all the drops have been placed on the arm a lancet is placed through each allergen droplet and this gently grazes the surface of the skin. No blood will be drawn but this graze allows a tiny amount of allergen to pass into the skin. Inside the skin of an allergic person specialised immune cells that cause an immediate hypersensitive reaction detect the allergen and release chemicals that cause inflammation. The resulting small red swollen patch is called a wheal (inflammation) and erythma (swelling).
3. After approximately 15 minutes the clinician measures the size of swelling and inflammation. Each measurement is then compared to the control. If the size of inflammation is smaller than the negative control then the person is not allergic to the allergen being tested. If the size of wheal falls between the negative and positive controls (when used) the clinician is able to score how allergic the person is to each allergen being tested.
4. Skin prick testing is a simple and speedy way to determine allergies. Suspicions about a patients allergy can quickly be confirmed and the appropriate advice or treatment regime can then be given. After skin prick testing the patient can be told exactly what they are allergic to and they will know what allergen sources they have to avoid in the future, or they can be assured that they are on the treatment regime appropriate for their condition.
Unlike some allergy testing, such as applied kinesiology, Bryans test, VEGA and hair analysis, skin prick testing has a solid scientific background. If you are interested in finding out more about how a skin prick test works follow this link:
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