Allergy tests can cause itchiness locally. It is rare, but some may have a severe allergic reaction to allergens used in testing. Your condition will be monitored after the test to manage any negative reactions.
What to Expect
Prior to Test
Keep a diary of your allergy symptoms. When you have symptoms, write them down, including:
- What time it happened
- Where it happened
- What you ate
- What you have come in contact with
For certain tests, you may be asked to stop certain medications before the test.
Description of the Test
There are several types of allergy tests:
- Blood testing—You will be asked to sit. An area inside your elbow will be cleaned with an antiseptic wipe. A large band will be tied around your arm. The needle will then be inserted into a vein. A tube will collect the blood from the needle. The band on your arm will be removed. After all the blood is collected, the needle will be removed. Some gauze will be placed over the site to help stop bleeding. You may also be given a bandage to place over the site. The process takes about 5-10 minutes. The blood will be tested to see if it reacts to certain substances.
- Skin testing—The suspected cause of your allergic reaction will be applied directly to your skin. It may be applied with a shallow scratch or with a skin-prick needle. The needle will push the substance into the upper layer of your skin. For every allergen tested, you will have a separate scratch or skin prick. Redness and swelling will appear if you are allergic. It usually takes about 15-20 minutes to appear. This may be followed by intradermal testing. In this case, the allergen is placed deeper into the skin.
- Patch testing—Patches containing suspected allergens are placed on the skin. The patches will be left in place for 48 hours. You will be asked not to shower or get them wet. They will then be removed. The skin will be examined after 48-96 hours. If there is a reaction, the skin will become itchy at the site. A blister-like lesion may form.
An antihistamine may be advised after the test. This can reduce itchiness at the test site. For severe allergies, make sure you have your EpiPen available if you use one.
How Long Will It Take?
- For blood testing: a few minutes
- For skin testing: 15-20 minutes
- For patch testing: 48 hours with the patch on, 48-96 hours for observation
Will It Hurt?
You may have mild irritation where the substance is applied to the skin. The needle pricks are small but can be irritating.
Skin and patch test results are available right away. Blood test results may take more time.
Avoiding your specific allergens will help lessen your symptoms. You and your doctor can also discuss additional steps to help control your allergic reactions.
Many factors can affect the reliability of lab tests. A test may suggest an illness that actually does not exist. This called a false positive. A test may also miss an illness that actually does exist. This is called a false negative.
A doctor will consider the results from many tests and your symptoms before making a diagnosis. It is important to discuss these results with your doctor before making any conclusions.