Skin Test to Diagnose Your Allergy
A skin allergy test is used to find out which substances cause a person to have an allergic reaction. This test has alternative names such as patch-allergy test, initial-allergy test and RAST test.
How this test is done
There are three common methods of testing skin allergies.
The skin prick test is done by:
- Placing a small number of substances that can cause your symptoms on the skin, usually on the forearm, upper arm, or back.
- The skin is then pricked so that the allergen enters under the surface of the skin.
- The doctor monitors the skin for swelling and redness or other signs of a reaction. Results are usually seen within 15 to 20 minutes.
- Several allergens can be tested at the same time.
Intradermal skin testing is done by :
- Inject a small amount of allergen into the skin.
- The health care provider then monitors the reaction at the injection site.
- 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 tests are a method for diagnosing the cause of a skin reaction that occurs after the substance has touched the skin:
- Suspected allergens are applied to the skin for 48 hours.
- Health care providers will see the area tested in the range of 72 to 96 hours.
Before an allergy test, the health care provider will ask about:
- Another disease you have
- 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 to avoid and when to stop using them before the test
Will this test hurt?
Skin tests can cause very mild discomfort when the skin is pricked.
You may have symptoms such as itching, nasal congestion, runny and red eyes, or skin rashes if you are allergic to the substance in the test.
In rare cases, people can have an entire body allergic reaction (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?
Allergy tests are done to determine what substances are causing your allergic symptoms. Your doctor may order a skin allergy test if you have:
- Allergic rhinitis and asthma that are not well controlled with medication
- Itching and angioedema
- Food allergies
- Skin rash (dermatitis), where the skin becomes red, sore, or swollen after contact with the substance
- Penicillin allergy
- Toxic allergy
Allergy to penicillin and related drugs are the only drug allergies that can be tested using a skin test. Skin testing for allergies to other drugs can be dangerous.
The 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 danger of severe allergic reactions.
Normal results
Negative test results mean there are no skin changes in responding 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 still be allergic to the substance.
What is the meaning of abnormal results
Positive results mean you react to a substance. The doctor will see a red and swollen area of the body called the wheal. Often, positive results mean the symptoms we are experiencing are due to exposure to these substances. In general, a strong response means you are more sensitive to the substance. People can have positive responses 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 allergen dose 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.
