How It Is Done continued...
An alternative skin prick method uses a device with 5 to 10 points (heads), which are dipped into bottles that contain the allergen extract. This device is pressed against the skin of the forearm or back so that all heads are pressed into the skin at the same time.
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.
Skin patch test
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.
- 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.
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 found, it may mean you are allergic to a certain allergen.