WHAT IS PATCH TESTING?
Patch testing is a procedure in which a patient is tested for allergies to chemicals and metals known to cause allergic contact dermatitis. The contact allergens (the chemicals and metals) are placed on “patches” on the back for 2 days. Each patch is a piece of tape approximately 2 x 4 inches containing 10 shallow aluminum or plastic wells/discs and one allergen is placed in each well/disc. Sometimes the patient is also tested with his/her own personal care products.
36 of the most common allergens are available in an FDA approved product called “True-test.” True-test is widely used by dermatologists and is often very helpful. However, research has shown that True-test misses relevant contact allergens in a significant number of patients. Dr. Feigenbaum and other members of the American Contact Dermatitis Society (ACDS) who specialize in the treatment of contact dermatitis often patch test with a larger panel of allergens. For example, the “North American Contact Dermatitis Group” (NACDG) 70 allergens series and “American Contact Dermatitis Society” (ACDS) 80 allergen series both make extensive use of these additional allergens. These additional allergens are not FDA approved and are usually shipped from Sweden or Germany.
Dr. Feigenbaum customizes the testing depending on the location of the patient’s dermatitis and any occupational or other exposures.
We usually test 120-140 allergens and carry the following series:
North American Contact Dermatitis Group 70 series
American Contact Dermatitis Society series
Rubber Chemical Series
(To our knowledge, most practices in San Diego test with 36-80 allergens.)
HOW DO THE VISITS WORK?
The patches are usually placed on your back and/or upper arms at the 1st visit and should remain well secured for 48 hours. It's optimal that you not take a shower or get sweaty for the 48 hours that the patches are on your skin. However, if this is not practical for you, we can use water-resistant patches or patch coverings which allow light exercise and a quick shower. (Some other practices offering patch testing require avoidance of showering/exercise for 4-5 days.)
The patches are removed at the 2nd visit.
2-3 days after removal of the patches, a 3rd visit is necessary for final “reading.” This three visit approach is standard for this testing. Please allow an hour for the first visit, and 30 min. for the second and third visit.
To allow for the proper timing between visits, the 3 visits can be scheduled on either
Mon, Wed, Fri (In Hillcrest)
Wed, Fri, and the following Mon (In Hillcrest)
Some itching under the patches is possible during the test, but this is usually mild. You can take an antihistamine, such as Benadryl, Claritin or Zyrtec, for the itching without interfering with the test. Prednisone and other oral steroids will interfere with the test.
If you are interested in other allergy testing, such as food allergy testing, environmental/airborne allergy testing, or penicillin allergy testing, this can usually be combined with your 2nd or 3rd patch testing visit.
HOW ARE THE RESULTS INTERPRETED?
A “positive” reaction to a particular chemical allergen may involve some combination of redness, swelling, blistering, and itching at the test site. Any positive reactions are expected to resolve completely over a few days or perhaps weeks, however it's theoretically possible that some patients with extremely sensitive skin could develop a change in skin color or texture, long-term, at the site of a positive reaction.
No medical test is perfectly “accurate.” According to the medical literature, patch testing has a 20% “false positive” rate, meaning that a test is positive but the patient is not allergic. Patch testing is also thought to have a 20% false negative rate, meaning that the test is negative but the patient really is allergic. Regardless, our patients and referring dermatologists have told us that patch testing, and the resulting allergen avoidance, has been very helpful for this condition.
WHAT HAPPENS AFTER THE PATCH TESTING?
After the 3rd patch visit, we will log into the members-only American Contact Dermatitis Society database and will email you a PDF list of your test positive allergens and a shopping list of “Approved” personal care products, detergents, etc not containing your test positive allergens or any cross-reacting allergens. Just take the Approved Products list or use the app which allows you to scan products with your phone), go to the store, and buy shampoo, conditioner, soap, cosmetics, etc from The List. We’ll walk you through the process.
For optimal results, for a 2-3 week period, you would want to put your usual products aside and ONLY use Approved products from the list. This way, you don’t need to read labels on bottles, trying to decipher complicated chemical names in tiny print. (e.g. methyldibromo glutaronitrile, 1,3-diphenylguanidine, methylisothiazolinone, 2-hydroxyethyl methacrylate)
IS PATCH TESTING COVERED BY MY HEALTH PLAN?
This testing has been covered in the past for all health plans with which we participate. If you have questions about this, please call your health plan and let us know if they tell you otherwise because it's likely an error on their part. CPT code 95044, diagnosis code L23.89. If your health plan requires an office visit co-pay, it's possible that you will have an office visit co-pay for each of the three visits. Please call us with any questions about this.
I’M USING THE SAME PRODUCTS. WHY WOULD I DEVELOP CONTACT DERMATITIS NOW?
When you buy shampoo, conditioner, deodorant or other personal care products, you are basically buying a mixture of various chemicals-- emulsifiers, preservatives, fragrances, etc and some company called that chemical mixture a "shampoo." Many of these chemicals are common contact allergens. It's a myth that people are more likely to develop allergies as they get older. However, one can always develop a new allergy to a chemical or metal contact allergen, resulting in allergic contact dermatitis.
In addition, it's unlikely that you are routinely reading the ingredients in your favorite products. There's nothing stopping a manufacturer from changing the chemical ingredients of a product, even if the name of the product and the container remain unchanged. Obviously if the manufacturer adds a new chemical to which you are allergic, you could develop a new rash due to allergic contact dermatitis.
IS PATCH TESTING INDICATED FOR MY RASH?
According to the literature, indications for patch testing may include:
Persistent eczematous eruptions when contact allergy is suspected.
Any chronic dermatitis, especially when involving the hands, feet, face, or eyelids.
Eczematous dermatitis in individuals involved in high risk occupations for contact dermatitis (eg, health care workers, dental assistants, cosmetologists, machinists, or rubber and plastic workers).
Patch testing also may be indicated when allergic contact dermatitis (ACD) is suspected as a complication of:
(Brod, BA. Patch Testing. UpToDate 2015)
Bernard A. Feigenbaum, M.D. FACP, FAAAAI
Helping You Understand Your Immune System and Take Control of your Health.
San Diego Allergy, Asthma & Immunology Consultants
Eczema/Atopic Dermatitis--Food Allergy Test to wheat, soy, milk, peanut, seafood and other foods (results in 15 min)
Allergic Contact Dermatitis--Comprehensive Patch Testing with 80-140 chemical and metal contact allergens, customized for each patient including: