How to Perform Skin Testing

It’s the middle of the day and you have just finished assisting an attending physician during the rounds. Written in the chart are new orders, included therein is an order of Cefuroxime 750mg Q8H after negative skin test. Understanding that you need to perform skin testing prior to the administration of the drug, you review the procedure. Here’s how it is done.

image022Prior to allergy testing, the patient will most likely be told to stop taking the following medications because they can affect the test results:

  • antihistamines (both prescription and over-the-counter brands)
  • certain heartburn medications
  • omalizumab (Xolair) (an asthma medication)
  • tricyclic antidepressants

Scratch test

  • During this test, an allergen is placed on a section of the patient’s skin with the use of a special tool to scratch the skin’s surface.
  • The patient will be closely monitored to see how the skin reacts to the foreign substance.
  • The health care provider closely watches the skin for swelling and redness or other signs of a reaction. Results are usually seen within 15 to 20 minutes.
  • If there is no swelling or redness on the skin, then, the patient is not allergic to that specific allergen.
  • Several allergens can be tested at the same time.

Intradermal skin test

  • If the scratch test is inconclusive, the doctor may order an intradermal skin test. This involves injecting a tiny amount of allergen into your skin.
  • During this test, a small amount of the allergen solution is injected into the skin.
  • An intradermal allergy test may be done when a substance does not cause a reaction in the skin prick test but is still suspected as an allergen for that person.
  •  The intradermal test is more sensitive than the skin prick test but is more often positive in people who do not have symptoms to that allergen (false-positive test results).

Patch test

  •  This involves using adhesive patches treated with suspected allergens.
  •  The patches will remain on the body after the patient leaves the doctor’s office. The patches are then reviewed at 24 hours after application and again at 48 hours, if necessary.
  • The health care provider will look at the area in 72 to 96 hours

Sources:

http://www.webmd.com/allergies/allergy-tests
http://www.healthcommunities.com/allergy-testing/skin-tests-for-allergies.shtml
http://www.nlm.nih.gov/medlineplus/ency/article/003519.htm
http://www.mayoclinic.org/tests-procedures/allergy-tests/basics/what-you-can-expect/prc-20014505

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