Contents:
- Medical Video: Skin Prick Test (Allergy Test) - John Hunter Children's Hospital
- How this test is done
- Will this test hurt?
- Why this test is done
- Normal results
- What does the abnormal result mean?
Medical Video: Skin Prick Test (Allergy Test) - John Hunter Children's Hospital
Skin allergy tests are used to find out substances that cause a person to have an allergic reaction. This test has alternative names such as patch tests - allergies, initial tests - allergies and RAST tests.
How this test is done
There are three general methods of testing skin allergies.
The skin prick test is done by:
- Placing a small amount of a substance that can cause your symptoms on the skin, usually on the forearm, upper arm, or back.
- The skin is then pierced so that the allergens enter under the surface of the skin.
- Doctors monitor the skin for swelling and redness or other signs of reaction. Results are usually seen in 15 to 20 minutes.
- Some allergens can be tested at the same time.
An intradermal skin test is performed with:
- Inject small amounts of allergens into the skin.
- The health care provider then monitors the reaction at the injection area.
- This test is more used to find out if you are allergic to bee venom or penicillin or can be used if the skin prick test is negative and the provider still thinks that you are allergic to allergens.
Patch test is a method for diagnosing the cause of a skin reaction that occurs after the substance touches the skin:
- Suspected allergens are placed on the skin for 48 hours.
- Health care providers will see areas tested in the 72 to 96 hour range.
Before an allergy test, the health care provider will ask about:
- Other illnesses that you have suffered
- Where you live and work
- Lifestyle
- Food and eating habits
- Allergy medications can change the results of skin tests. Your doctor will tell you about medicines that should be avoided and when to stop using them before the test
Will this test hurt?
Skin tests can cause very mild discomfort when the skin is pierced.
You may have symptoms such as itching, nasal congestion, watery and red eyes, or skin rashes if you are allergic to the substance in the test.
In rare cases, people can have all the body's allergic reactions (called anaphylaxis), which can be life-threatening. This usually only happens with intradermal testing. Doctors will be prepared to treat this serious response.
Why this test is done
An allergy test is done to determine what substances cause your allergic symptoms.Your doctor may request a skin allergy test if you have:
- Allergic rhinitis and asthma are not well controlled with drugs
- Itching and angioedema
- Food allergy
- Skin rash (dermatitis), in which the skin becomes red, sore, or swollen after contact with the substance
- Penicillin allergy
- Poison allergy
Allergy to penicillin and related drugs is the only drug allergy that can be tested using a skin test. Skin tests for allergies to other drugs can be dangerous.
A skin prick test can also be used to diagnose food allergies. Intradermal tests cannot be used to test food allergies because false positive results will be high and cause the danger of a severe allergic reaction.
Normal results
A negative test result means there are no skin changes in response to allergens. This negative reaction means that you are not allergic to the substance.
In rare cases, a person may have a negative allergy test and is still allergic to the substance.
What does the abnormal result mean?
Positive results mean you react to a substance. The doctor will see the red and swollen areas of the body called wheal. Often, positive results mean that the symptoms we experience are due to exposure to these substances. In general, a strong response means you are more sensitive to substance.People can have a positive response to substances with allergic skin tests, but do not have problems with these substances in everyday life.
Skin tests are usually accurate. However, if the dose of allergens is large, even people who are not allergic will have a positive reaction.
Your doctor will consider the symptoms and results of your skin test to suggest changes in your lifestyle to avoid substances that can cause your symptoms.
