How It Is Done continued...

If the skin prick test is negative, you may choose to have an intradermal skin test at a later visit. A skin prick test is usually done first because the intradermal test has a greater chance of causing a severe allergic reaction.

The skin prick test and the intradermal test usually take less than an hour each.

A skin patch test also uses small doses of the suspected allergen. For this test:

• Doses of allergens are placed on patches that look like adhesive bandages.
• The patches are then placed on the skin (usually on your back). This usually takes about 40 minutes, depending on how many patches are applied. See a picture of a skin patch allergy test.
• You will wear the patches for 24 to 72 hours. Do not take a bath or shower or do any activities that could make you sweat excessively while you are wearing the patches. This could loosen the patches and cause them to fall off.
• The patches will be removed by your health professional, and your skin will be checked for signs of an allergic reaction.

Blood test

The health professional drawing your blood will:

• Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
• Clean the needle site with alcohol.
• Put the needle into the vein. More than one needle stick may be needed.
• Attach a tube to the needle to fill it with blood.
• Remove the band from your arm when enough blood is collected.
• Apply a gauze pad or cotton ball over the needle site as the needle is removed.
• Apply pressure to the site and then a bandage.

The blood sample will be placed on specially treated paper and sent to a lab to determine whether antibodies to any of the allergens being tested are present. If specific antibodies are detected, it may mean you are allergic to a certain allergen.

How It Feels

Skin tests

With the skin prick test and the intradermal skin test, you may feel a slight pricking sensation when the skin beneath each sample is pricked or when the needle penetrates your skin.

If you have an allergic reaction from any of the skin tests, you may have some itching, tenderness, and swelling where the allergen solutions were placed on the skin. After the testing is done, cool cloths or a nonprescription steroid cream can be used to relieve the itching and swelling.

If you are having a skin patch test and you have severe itching or pain under any of the patches, remove the patches and call your health professional.

Blood test

You may feel nothing at all from the needle puncture, or you may feel a brief sting or pinch as the needle goes through the skin. Some people feel a stinging pain while the needle is in the vein. But many people do not feel any pain or have only minor discomfort after the needle is positioned in the vein.