Patch testing helps to confirm a diagnosis of allergic contact dermatitis, which is a type of skin rash that occurs when certain substances come in contact with the skin. Examples of these substances, known as allergens, may include fragrance in perfume, adhesives used in bandages, metals found in jewelry, and glues used in shoes, just to name a few.
Anyone can develop skin irritation (also called contact dermatitis) when exposed to harsh chemicals like strong detergents, household cleaners, solvents, and acids. However, reactions to allergens are different. Only some people will develop contact dermatitis when exposed to allergens. That’s why you may be the only person you know that experiences a rash when coming in contact with a particular allergen]. A patch test is not the same as a scratch or prick test (often performed by an allergist). Patch testing cannot identify allergies to foods, inhaled substances, or oral medications.
How Patch Test Performed?
Strips of tape containing small quantities of common allergens will be applied to the skin of your back during your first visit, which may last about 45 minutes. The allergens must remain in place and be kept dry for 48 hours.
After the 48 hours, the patches will be removed and an initial reading will be performed. The patch sites will be outlined with a marker, and you will be asked to return for a final reading on another day.
A positive test will show a red, raised area of skin, often with itching. A strong reaction could cause blistering and, very rarely, a prolonged reaction (lasting several weeks) or scarring.
Metal contact allergy is a delayed-type hypersensitivity reaction to metal. The most common offender is nickel; however, sensitization occurs to many other metals. Patch testing to the common metals prior to placement of a prosthetic device will identify patients who are sensitized. At Bernstein Allergy Group, we have developed a customized orthopedic patch panel for the common sensitizing metals in orthopedic prostheses and methyl methacrylate, a potential sensitizer in surgical cement products.