What do skin allergy tests test for
Blood tests may be used instead of, or alongside, skin prick tests to assist diagnose common allergies.
A sample of your blood is removed and analysed for specific antibodies produced by your immune system in response to an allergen.
Patch tests are used to investigate a type of eczema known as contact dermatitis, which can be caused by your skin being exposed to an allergen.
A little quantity of the suspected allergen is added to special metal discs, which are then taped to your skin for 48 hours and monitored for a reaction.
If you own a suspected food allergy, you may be advised to avoid eating a specific food to see if your symptoms improve.
After a few weeks, you may then be asked to eat the food again to check if you own another reaction.
Do not attempt to do this yourself without discussing it with a qualified healthcare professional.
A microscopic quantity of an allergen is introduced to a patient’s skin by various means:
- Skin scrape Test: a superficial scrape is performed with assist of the bovel of a needle to remove the superficial layer of the epidermis.
- Skin prick test: pricking the skin with a needle or pin containing a little quantity of the allergen.
- Skin scratch test: a deep dermic scratch is performed with assist of the blunt bottom of a lancet.
- Intradermic test: a tiny quantity of allergen is injected under the dermis with a hypodermic syringe.
- Patch test: applying a patch to the skin, where the patch contains the allergen
If an immuno-response is seen in the form of a rash, urticaria (hives), or (worse)anaphylaxis it can be concluded that the patient has a hypersensitivity (or allergy) to that allergen.
Further testing can be done to identify the specific allergen.
The «skin scratch test» as it is called, is not extremely commonly used due to increased likelihood of infection. On the other hand, the «skin scrape test» is painless, does not leave residual pigmentation and does not own a risk of infection, since it is limited to the superficial layer of the skin.
Some allergies are identified in a few minutes but others may take several days. In every cases where the test is positive, the skin will become raised, red and appear itchy. The results are recorded — larger wheals indicating that the subject is more sensitive to that specific allergen.
A negative test does not conclusively law out an allergy; occasionally, the concentration needs to be adjusted, or the body fails to elicit a response.
Delayed reactions tests
See also: Patch test
The patch test simply uses a large patch which has diverse allergens on it.
The patch is applied onto the skin, generally on the back. The allergens on the patch include latex, medications, preservatives, hair dyes, fragrances, resins and various metals.
Immediate reactions tests
In the prick, scratch and scrape tests, a few drops of the purified allergen are gently pricked on to the skin surface, generally the forearm. This test is generally done in order to identify allergies to pet dander, dust, pollen, foods or dust mites. Intradermal injections are done by injecting a little quantity of allergen just beneath the skin surface.
The test is done to assess allergies to drugs love penicillin or bee venom.
To ensure that the skin is reacting in the way it is supposed to, every skin allergy tests are also performed with proven allergens love histamine, and non-allergens love glycerin. The majority of people do react to histamine and do not react to glycerin. If the skin does not react appropriately to these allergens then it most likely will not react to the other allergens.
These results are interpreted as falsely negative.
Skin finish point titration
Also called an intradermal test, this skin finish point titration (SET) uses intradermal injection of allergens at increasing concentrations to measure allergic response. To prevent a severe allergic reaction, the test is started with a extremely dilute solution. After 10 minutes, the injection site is measured to glance for growth of wheal, a little swelling of the skin. Two millimeters of growth in 10 minutes is considered positive. If 2 mm of growth is noted, then a second injection at a higher concentration is given to confirm the response.
The finish point is the concentration of antigen that causes an increase in the size of the wheal followed by confirmatory whealing. If the wheal grows larger than 13 mm, then no further injection are given since this is considered a major reaction.
In a few cases, a test called a food challenge may also be used to diagnose a food allergy.
During the test, you’re given the food you ponder you’re allergic to in gradually increasing amounts to see how you react under shut supervision.
This test is riskier than other forms of testing, as it could cause a severe reaction, but is the most precise way to diagnose food allergies.
And challenge testing is always carried out in a clinic where a severe reaction can be treated if it does develop.
Skin prick testing
Skin prick testing is one of the most common allergy tests.
It involves putting a drop of liquid onto your forearm that contains a substance you may be allergic to.
The skin under the drop is then gently pricked.
If you’re allergic to the substance, an itchy, red bump will appear within 15 minutes.
Most people discover skin prick testing not particularly painful, but it can be a little uncomfortable. It’s also extremely safe.
Make certain you do not take antihistamines before the test, as they can interfere with the results.
Allergy testing kits
The use of commercial allergy-testing kits isn’t recommended.
These tests are often of a lower standard than those provided by the NHS or accredited private clinics, and are generally considered to be unreliable.
Allergy tests should be interpreted by a qualified professional who has detailed knowledge of your symptoms and medical history.
Sheet final reviewed: 22 November 2018
Next review due: 22 November 2021
This article is about the method for medical diagnosis of allergies.
For other uses, see Scratch test (disambiguation).
Skin allergy testing or skin prick test is a method for medical diagnosis of allergies that attempts to provoke a little, controlled, allergic response.