Patch testing considerations
There are a few things to be mindful of before patch testing a patient. It is useful to know the following:
Patch testing and pregnancy & breastfeeding
- At SHI, we avoid patch testing in the first trimester of pregnancy, because the side effects of patch testing on the baby are unknown
- Patch testing is considered safe in the 3rd trimester, if absolutely necessary. Otherwise wait until the baby is born
- On the other hand, some believe that patch testing in pregnancy should not be performed despite a lack of evidence suggesting that allergens used during testing could pass through to the foetus.
- Patch testing a breastfeeding mother is considered to be safe.
Patch testing on medication
- Oral corticosteroids should ideally be ceased at least 48 hours before testing.
- 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 aware that 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 during the period of testing. If applying on an 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 as they will not affect test results. However, they can impact prick testing results.
- Medications such as methotrexate, azathioprine 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.
- When patch testing on dupilumab try and maximise the time between the last injection and commencing patch testing.
- When patch testing on upacitinib (Rinvoq) stop on the Friday before testing (if patch testing starts on the Monday).
There is not a lot of data available on these drugs and how they impact patch testing results. We know some drugs diminish or reduce the strength of the reactions, possibly leading to false negative reactions. Please refer to the Systemic Therapies Information Sheet for more detail.
Patch testing, sun exposure and phototherapy
- There should be no sun exposure or phototherapy to the back for a minimum of 7 days prior to testing. Theoretically sunlight exposure before testing may reduce the immune response of the skin (and therefore affect the test results), although clearcut evidence is lacking.
Patch testing on eczematous skin
- Patch testing on rashy or eczematous skin is generally discouraged, as patch testing on such skin can cause a flare up, therefore making reading of results difficult
- We would recommend avoiding applying patches on areas of skin that have an active rash and to consider patch testing once the skin has improved
- Occasionally a patient with severe eczema or 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, be aware that reactions may be lessened as a result
- Be cautious when applying patches to skin with recent eczema or very dry skin. Some patches can stick too firmly and be difficult to remove.
Patient preparation
Prior to patients attending for their patch testing appointments there are a few important things to know to ensure the patch testing process goes as smoothly.
- Ask the patient if they have any problems with medical tapes or dressings. Refer to the Tape Allergies Information Sheet for details about how to manage this situation. If a patient is allergic to the patch testing tapes, an alternative patch type will need to be used.
- Send out an information sheet about avoiding fragrances and the preservative methylisothiazolinone, to all people prior to their patch testing appointment. Sometimes this avoidance improves the persons rash and they may no longer need patch testing.
- Remind the patient 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 thin, light moisturising lotion can be applied by the patch testing nurse before patch application. Allow the moisturiser to soak in and skin to dry approx. 20 mins before applying the patches.
- Patients should shower the morning before testing as they cannot get their back wet during the patch test process (from the time the patches go on until after their final appointment). Some patients manage to shower their front, especially if they have a hand-held shower, being mindful to keep the back dry.
- Patients 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 from 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.
Patients’ own samples
Patients are required to bring their own products for testing, in the original containers where possible (so labels and ingredient listings 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, liquid soaps, hand cleansers, cosmetics and nail polish)
- Products specific to the area of the skin affected e.g. gloves in case of 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 for all products a patient may come into contact with in the workplace. Encourage the patient to get information from the workplace Occupational Health & Safety 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
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