Section 5.3 Practical Aspects Of Patch Testing

Patch testing considerations

There are a few things to be mindful of before patch testing starts for a patient. In most circumstances the dermatologist will be aware of most of these situations, but it is useful to know the following:

Patch testing and pregnancy & breastfeeding:

  • Generally, at the Skin Health Institute, Melbourne, we avoid patch testing in pregnancy, because the side effects of patch testing on the baby are unknown. However, we will consider it in the 3rd trimester if necessary. All this information should be explained to the patients.
  • It is suggested, patch testing in pregnancy is not normally performed for medico-legal reasons, even though there is no evidence suggesting that allergens used during testing could pass through to the fetus10.
  • Patch testing a mother who is breast feeding is considered to be safe. However, some centres do not patch test breast feeding women either, primarily due to the lack of information about possible implications on mother and baby. At the Skin Health Institute, Melbourne we do patch test during breast feeding.

Patch testing and medication:

  • Oral corticosteroids should be ceased at least 48 hours before testing. However, on rare occasions, those with severe dermatitis or eczema may have to continue on a small dose (5-10mg maximum) to ensure the skin is maintained at a level where patch testing is possible. The dermatologist conducting the patch testing should be consulted if the patient is taking oral steroids. This should also be noted when reactions are being read as the strength of reactions may be reduced.
  • Topical corticosteroids may be continued, except on the back on during the period of testing. If applying on area where patches are to be applied, topical steroid use should be ceased 3-7 days beforehand. If ceased closer to the period of testing, be mindful of false negative reactions.
  • Antihistamines may be used if itching is a concern for the patient, as they will not affect test results.
  • Medications such Methotrexate, Imuran and Cyclosporine may be continued during the patch testing process, as long as the dermatologist is aware of this.
  • Other medications such as antibiotics can also be taken during the patch testing process, as they do not impact on patch testing results.

Patch testing, sun exposure and phototherapy

  • There should be no sun exposure or phototherapy to the back for 7 days prior to testing. It is thought sunlight before testing may reduce the immune response of the skin (and therefore affect the test results)10.

Patch testing and eczema or rashes:

  • Patch testing on rashy/eczematous skin is generally discouraged, as patch testing on such skin can cause a flare up of the rash/eczema, therefore making reading of results difficult.
  • If a patient has rashy skin, they are often given medications to help improve condition of the skin. Once skin has improved patch testing can then occur. Occasionally a patient with severe eczema/dermatitis will be patch tested whilst on a low dose of oral corticosteroids, particularly if there is a risk that skin will deteriorate if they are stopped. However, it is important to be aware the extent of the reactions may be lessened as a result. A rule of thumb is to avoid applying any patches on areas of skin that have active rash.
  • It is also important to give caution to applying patches to skin that has had recent eczema as well, where the skin may be dry and scaly. Some patches can stick too firmly and be difficult to remove. See below for further information.
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Patient preparation

Prior to patients’ attending for their patch testing appointments there are a few important things they need to know to ensure the patch testing process goes as smoothly.

  • There should be no application of moisturiser on the back on the day of testing. The patient is able to continue normal moisturising routine on the rest of the body during testing.
  • If the patient has dry, scaly skin a think, watery moisturising lotion can be applied by the patch testing nurse before patch application. Allow the moisturiser to soak in and skin to dry approx. 15 mins then apply the patches.
  • Patients should shower the morning before testing, because they cannot get their back wet from the time the patches go on until after their final appointment with the dermatologist. Some patients still manage to shower their front, especially if they have a hand-held shower, being mindful to keep the back dry.
  • Men with hairy backs should shave or wax before attending, or nurses may have to shave on the day. Hair removal creams should not be used. If the back is hairy the tests do not stick, and also removing the patches will be uncomfortable. It is best if this happens a day or 2 before testing, so any irritation that may result from the hair removal has a chance to settle.
  • During testing, excessive sweating must be avoided as patches may fall off or loosen. People working in a job where heat and sweating are likely may need to perform modified duties at work during this time, or may require time off work. Physical activity where sweating is likely is also discouraged during this time. Sometimes a Medical Certificate may be required to facilitate the above.

Patient own samples

Patients are required to bring their own products for testing, in the original containers where possible (so labels and ingredient listing can be read).

Patients are encouraged to bring:

  • Skin care products (even if they don’t think it is causing their problems e.g. moisturisers, hand cleansers, cosmetics and nail polish)
  • Products specific to the area of the skin affected e.g. gloves if you have hand dermatitis or shoes and socks if feet are affected.
  • Work samples – either bring them in the original containers if not too big, or put a small sample amount into individual screw top glass container and label
  • Safety Data Sheets (SDS) for all products and chemicals a person may come into contact with in the workplace. Encourage the patient to get information from OHS representatives, union officials, supervisor or employer. It is compulsory for workplaces to supply these.
  • The patient should bring their own samples to all appointments during the patch testing process.

Appointments – what happens at each appointment?

Once a patient has a referral from a dermatologist, the patient liaises with the clinic administration team to arrange an appointment. Relevant paper work is sent to the patient.

The patient is required to attend 3 appointments: However, as mentioned previously, this may vary from patch testing clinic to clinic. Below is an example of how the patch testing process works at the Skin Health Institute, Melbourne.

1st appointment (Monday) – Patient meets with the Dermatologist who takes a thorough history in the electronic notes system PatchCams©. They determine what to test the patient to and then construct a chart with the allergens listed, and also document all the patients’ own samples to be tested and the dilutions that these should be tested at. Some products or chemicals need to be diluted as they are too strong to be directly applied to patients’ skin. The nurses make up the required tests and place patches on the patients back (and occasionally arms).

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On occasion, some patients are required to have a blood test. This is most often a blood serum test (formerly a RAST test), often for latex and sometimes other allergens such foods, animals, or grasses and total IgE.

2nd appointment (Wednesday) – The patient returns and the patches are removed. Occasionally additional tests are added. Once patches are removed, the patient will see the dermatologist who performs a ‘reading’ to see if there have been any reactions. Positive results are red, raised itchy spots, as seen in the image below. Any UVA for sunscreen separates is performed on this day, after the patch tests have been removed.

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Example of positive patch test results.

3rd appointment (Friday) – This is the patient’s final appointment. If any additional tests were added, these are removed. The patient will spend approximately 20-30 minutes with the dermatologists where they will be told about any reactions to the tests, have their diagnosis and management explained, including any skin care advice. The Diagnostic Flowchart developed by Associate Professor Rosemary Nixon is a useful tool to use on this day and provides a practical description of the diagnosis for the patient (See attachment 1).

Some centres offer day 7 reading for results as well, which can help identify any late reactions. More information about late reactions on page?

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