Patch Testing


Dermatologists apply patch tests in patients with dermatitis, to find out whether their skin condition may be caused or aggravated by a contact allergy. Patch tests are not the same as skin prick tests, which are used to diagnose hay fever allergy (house dust mite, grass pollens and cat dander). Skin prick tests have very limited value for patients with skin rashes.

Dr. Groysman received extensive training in allergy testing. She was selected to become a member of American Contact Dermatitis Society and has access to extensive allergy database that only a few doctors have.

A range of substances can be used for patch testing. North American test patch series are applied to nearly every patient, together with specific tests appropriate to the individual. Each substance (known as an allergen) has been tested to find the best concentration to demonstrate an allergic reaction without causing irritation to those who are not allergic to the material.

Patch Testing

Standard Patch Tests
Standard Patch Tests

The Appointments

The first appointment will take about half an hour. Tiny quantities of 70 materials in individual square plastic or round aluminium chambers are applied to the upper back. They are kept in place with special hypoallergenic adhesive tape. The patches stay in place undisturbed for 72 hours. You may take antihistamines during the 72 hrs, but not oral steroids. You will return at 72 hrs to get patch test reading.

At the second appointment, usually three days later, the patches will be removed. The back is marked with an indelible black felt tip pen or other suitable marker to identify the test sites.

The Results

Dr. Groysman will complete a record form at 72hrs. The result for each test site is recorded. The system we use is as follows:

  • Negative (–)
  • Irritant reaction (IR)
  • Equivocal / uncertain (+/–)
  • Weak positive (+)
  • Strong positive (++)
  • Extreme reaction (+++)

Irritant reactions include sweat rash, follicular pustules and burn–like reactions. Uncertain reactions refer to a pink area under the test chamber. Weak positives are slightly elevated pink or red plaques. Strong positives are ‘papulovesicles’ and extreme reactions are blisters or ulcers. The relevance depends on the site and type of dermatitis and the specific allergen. The interpretation of the results requires considerable experience and training.

You will be given a printout of the allergens that you are allergic to. You will also be emailed a product list of all products that you can use on regular basis.

Positive Patch Test Reactions

Patch Testing

Notes

  • Do not expose your back to the sun for four weeks before your patch tests
  • Do not take oral steroids before your patch test
  • Wear old clothing; felt tip pen marks can stain clothes
  • Do not swim, rub, or exercise, as the patches may come off
  • Keep the back dry, so no baths, showers or unnecessary sweating
  • Men with hair on their backs should shave or wax it off a day or two before testing (do not use chemical hair removal products).
  • Do not put any creams or oils on your back the morning of the testing.

Bring Your Own Materials For Testing

Discuss the particular substances with which you come into contact with your dermatologist; you may be asked to bring materials from home or work.

  • Provide your dermatologist with data sheets of industrial items with which you are in contact.
  • Bring or send all chemical items for testing at least a week before the first appointment so that they can be prepared for testing if necessary.
  • Only small quantities are required eg. a few drops or grains.
  • Label items carefully with their common and chemical names – provide data sheets if available.
  • Identified food items and plants (if relevant) should be brought fresh to the first appointment; ice block trays are useful to separate items.
  • Bring a selection of cosmetics to be tested (up to ten items) including nail varnish, moisturiser, sunscreen, perfume, shampoo. Soap is not usually tested (it always causes a reaction if left on the skin for two days).
  • Bring all prescribed and non–prescribed ointments, creams and lotions that you have used.
  • Relevant clothing including rubber gloves and footwear can be tested;

Adverse Reactions to Patch Tests

Positive patch test results are small areas of active eczema / dermatitis. They will be itchy and may require treatment with topical steroid.

  • Occasionally patch test reactions persist for several weeks.
  • Patch tests may provoke other areas of dermatitis to recur or to appear for the first time.
  • Although hypoallergenic tape is used, occasionally people react to all areas in contact with the tape.
  • An ‘angry back’ reaction may arise, particularly in a patient with active dermatitis at the time of testing, or in someone who has multiple positive reactions. ‘Angry back’ refers to false positives to many or all of the tested allergens.
  • Rarely, sensitisation to a new allergen may occur as a result of the test — this is revealed as a reaction occurring around 10 days after the test was applied.
  • Re–testing may be required, sometimes one allergen at a time, to confirm or clarify a reaction.
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