How are allergies diagnosed?
Skin Prick Testing
The most common way to test for Type I allergy is using a skin prick test (SPT). This is always completed in a clinic or hospital (never at home). A small amount of allergen will be put on a flat part of the body (e.g. inner arm) and a lancet will be used to prick the skin (most patients do not feel anything other than a little pressure); any allergen is then blotted away. After 15 minutes the arm is examined by a medical professional who will ascertain if there has been a reaction. This along with a full medical history is used to diagnose allergies. A list of common allergens that can be used for SPT can be found here (link to list).
For some people SPT is not appropriate, e.g. those with certain medical conditions or on certain medications that they must take regularly, in which case a blood test can be taken.
Click the + on the below sections to read more on the science behind a skin prick test and what to expect from yours!
The Science
Allergopharma and Lofarma provide test solutions for skin prick testing, which are used for the diagnosis of lgE mediated allergic diseases (type 1, Coombs and Gell). The allergen extracts are manufactured from various allergenic raw materials of biological origin, such as pollen, epithelia, moulds, mites, dusts, and foodstuffs.
The genuine allergens are isolated with careful aqueous extraction at a physiological pH value. By means of modern technological methods, these solutions are further processed; an essential step is the removal of possible irritants of low molecular weight, using diafiltration techniques.
The resulting allergen solutions (allergen bulk extract) are characterized by in-process-controls, e.g. physico-chemical and immunological analysis, resulting also in a quantification on major allergens. In a final procedure, these allergen bulk extracts are converted by freeze-drying (lyophilisation) to allergen active substances, which can be stored for a long time. For the production of test solutions, the allergen active substances are diluted with the respective diluents to obtain the required diagnostic solutions.
As a rule, the concentration of allergens in the diagnostic solutions leads to distinct allergic skin reactions, provided that the patient has been sensitized accordingly.
Open the dropdown to the right to find out more about the skin prick test procedure.
What Happens During a Skin Prick Test?
Procedure
Skin prick tests are performed at the volar side of the forearm. In a first step the skin is marked with a pen, as shown on the right. Then one drop of each solution to be tested is put on the skin beside the respective mark.
Then the point of a prick needle or prick lancet is pushed through the drop and held against the skin for about 1 second. The shouldered skin prick test lancet just penetrates the skin allowing through a very small quantity of the solution.
Negative and Positive Control
Control tests are performed at the top and at the bottom of the skin test row, in order to determine the individual skin test sensitivity of the patient:
- Negative control test with physiological saline
- Positive control with a histamine solution.
Wheal
The test results can be read after a period of 10 to 20 minutes. Nevertheless, the development of the skin reactions should be observed in the meantime. A pale yellow wheal (oedema) surrounded by a red flare (erythema) is a positive test result. In order to evaluate the test results, the skin reaction to the histamine solution is to be taken into account, e.g. the sizes of the wheal and the red flare.
Patch Testing
To test for a Type IV allergy the most common way to diagnose is a ‘patch test’. Patch testing is carried out by a clinician and entails having patches pre-loaded with allergens, stuck to your back. Again, this will be carried out in a clinic. You will need to keep that patches in place for a couple of days, you will then have them removed. Your clinician will check the results after a further couple of days.
What is the reason for a patch test?
Patch Testing is a diagnostic method used by healthcare professionals to identify a Type IV Hypersensitivity or Type IV allergy, sometimes referred to as Allergic Contact Dermatitis. Type IV allergy tends to be associated with workplace allergens such as the chemicals used in hair salons, cosmetic products, and other small molecular weight chemicals.
Will the patch test be painful?
The patches are stuck on with a hypoallergenic glue. The application of the skin patch tests will not be painful. You may notice some itching or discomfort after a few hours or days – this is usually suggestive of a positive reaction. If you do find yourself itching try not to scratch as this can impact the results. You may also notice some small rashes on your back once the test has been removed. Your healthcare professional will look at these rashes to ascertain if you are allergic to a substance.
Is the test 100% accurate?
The patch test will be used alongside a clinical history – this will involves asking you some questions about things you may regularly come into contact with. Some medications may give a false result, so it is important you discuss and medicine you take with your healthcare provider.
What if the test shows I am allergic to something?
You can discuss potential treatments and method to avoid these things with your healthcare practitioner. There are a few products on the market that may be able to assist.
What Happens During and After a Patch Test?
Your healthcare provider will use a TRUE TEST patch testing kit to pinpoint the allergen causing your reactions they may also highlight other allergens that you did not realise you were allergic to. The patch test will be placed on your back, so make sure this area is accessible by wearing a loose-fitting top where possible. Make sure your back is clean and free from oils such as moisturisers. Your healthcare provider will then stick three patches to your back containing 35 potential allergens. They will also use a pen to mark your back. This helps the results to be read later.
Your healthcare professional may add a covering panel which will hold the test in place and will allow you to shower, although bathing is not advised. Speak to your patch tester to see if this protective panel has been used, if not you will need to refrain from showering. Try to avoid sweating and continue to wear loose-fitting clothing if possible. Do not sunbathe or use a UV sunbed whilst you have the patches on or afterwards. You will also need to refrain from taking any medication containing steroids. If you are prescribed steroid medication you must discuss this with your healthcare professional.
After 2 days the patch test will be removed. At this point you will be able to take a shower but try to avoid touching/rubbing/soaking the test area.
The results will be read by your healthcare professional a further 2-3 days after the patches have been removed.