Section 6.2 Patch Application

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Placement of patches

The placement of patch tests will depend on several factors:

  • The number of patches to be applied
  • The physical size of the patient
  • The condition of the skin where the patches are to be applied. Patches should not be placed on top of areas of active rash or erythema as they skin may flare, making reactions difficult to interpret.
  • Tattoos: patches should not be placed on top of tattoos, as reading the results can be difficult.
  • Shape of the back should also be considered: Avoid bony areas of back and skin folds as patches do not stick as well
  • The midline of the back should also be avoided as it is the sweatiest area, and patches may loosen.

Application of patches

Here are a few examples of ways the patches can be applied.

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Examples of alternative patch application

The patches should be applied in an orderly fashion across the back starting at the top left-hand side, working across to the right. The middle of the back should be avoided, because this is the most common place people sweat.

If there is insufficient space on the back due to rash or tattoos or there are a large number of patches to be applied (i.e. 12 or more patches), some patches can be applied to the arms.INSERT photo

When applying patches it is recommended that very bony parts of the back be avoided, as should bra strap areas (the horizontal strap), and with overweight people any excess skin folds should also be avoided, as patches applied in this area often don’t adhere firmly for the duration of testing.

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Occasionally patches may have to be applied sideways on the back because it allows more patches to be applied and follows the curvature of the back.

When placing patches sideways, always be consistent in the way the patches are applied and always ensure the top of the patch is always to the right (so the number on the bottom of the patch is to the left). This ensures that the numbers of the patches flow consecutively, making it easier to read results and match up with the chart.

Placement with tattoos

Tattoos can limit the amount of skin available for patch testing. It is important that patches are not applied on top of the tattoos, because it may not be possible to accurately read test results. Instead place them around the tattoo – you may be required to cut them in to smaller strips so they fit.
http://skinhealthinstitute.com.au/wp-content/uploads/2023/06/Tattoo Cousins, Terry .jpgThis is a good example of how to apply patches around a tattoo –you may need to be creative!

Once patches are applied to the back, use a surgical marker (or patch testing marker) to place marks next to each disc. These marks indicate to us where the patches were placed, so the doctor knows where each allergen was located. These will need to be ‘redrawn’ on the second appointment when patches are removed.

There are 2 different markers available, one from allergEAZE® and one from Chemotechnique.

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Depending on the type of patch used, Micropore™ may need to be placed over the top of the patches to hold them firmly in place. This is often needed if Finn Chambers are being used, however the allergEAZE® patch test chambers do not require extra taping, nor do the Chemotechnique Ultimate patch or Ultra patch. Micropore is now only needed when a patch has been cut down , e.g. 3 discs remain on the patch, as these small cut patches can sometimes fall off or get stuck onto clothes.

Sunscreen/UV separates

Sunscreen “separates” refers to patches that will need to be exposed to UVA light at the second visit (day 2). The purpose of this test is to determine if an allergic reaction is occurring as a result of the interaction of sun (UV) and sunscreen ingredients. After the patches have been removed (day 2), only the area of skin where the sunscreen separate patch was located is exposed to 5 joules of UVA 5, ideally using a hand and foot machine.

http://skinhealthinstitute.com.au/wp-content/uploads/2023/06/FullSizeRender (1).jpgSunscreen separate patches can be applied to the lower forearm, where possible, as this allows easy access for the UVA exposure, as the patient can be placed into the hand and foot UVA machine. This is easier than applying to the back, which then means the other patches have to be covered up so they are not exposed to the UVA. If they are applied to the lower forearm, ensure they are positioned so an adequate dose of UVA reaches the patch location.

The placement of these patches also needs to be drawn on the diagram on the patient chart.

If using PatchCams, the chart print-out will have a note at the top right-hand corner, stating that 5 joules UVA need to be applied on the second appointment after patches have been removed.

Videos to watch:

Photo patch testing

What not to do when applying patches….

Placement of patches can be difficult at times, particularly if there are a large number of patches to be applied, or if the patient has a small back, a rashy back or has a large tattoo. The picture below shows patches that have not been applied very well. On occasion, the doctor may not have realised how many tests they have actually selected to be applied – ask them to reconsider if all allergens are absolutely necessary if you don’t think they will fit. However in these images below, the patches could have been applied to arms, and not to the midline of the back.

Numbering of patch tests when applied to the patient

As mentioned earlier, the numbering system for patch testing can be confusing.

Once applied to the patients back, the patch numbers reverse (from what they were when the patches were being prepared. The picture below shows the numbering once the patches are stuck on the patient. This is particularly important, because the dermatologist/nurse doing the reading needs to fully understand the numbering, to ensure results are accurate.

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Here is an example of how the numbering works once applied to the back

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Each patch is numbered at the bottom. The patch should be applied to the patients’ back with this number at the bottom, as shown above. On each patch, there are 10 discs, each with a different substance on each disc.

On patch one = allergens 1-10 (top left-hand corner is number one and bottom right-hand corner is disc 10).

Patch 2 = 11-20 (top left-hand corner is disc 11 and bottom right-hand corner is 20)

Patch 3 = 21-30 (top left-hand corner is 21 and the bottom right-hand corner is 30)

And this continues for the number of patches applied.

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The image below demonstrates how the numbering location on each disc, matches up with the chart so each substance can be identified. For example, on the image below, numbers on each patch are as follows: number 1 allergen matches with number one on the chart, which is nickel, no. 2 is Balsam of Peru etc.

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Place the top of the patch on the right-hand side of the back. That way the numbers also flow in order, making it easier for the Dr. to know where all the patches have been.

Make sure location of patches and their numbers are documented on chart accurately, so the nurse and dermatologist both know where each patch and allergen are located.

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Instructions to give patients after patches are applied

Once patients have had patches applied to their back it is important to give them advice about how to care for their patches. It is also useful to give these instructions as an information sheet so they can read the important instructions once they return home.

This advice should include:

  • Don’t get the back wet for the period of testing. Have a shallow bath, wash from the hand basin or use a hand-held shower, sparing the back.
  • Avoid physical activity (including work) that will cause heat and sweating, as this may cause patches to loosen and on occasion can fall off. Some workers who have physical jobs may need time off work or modified duties. Consider a medical certificate if necessary.
  • Keep an eye on patches – place additional tape such as Micropore™ over the top of patches if they look like they are loosening.
  • Avoid scratching the back while patches are on, and after patches are removed. Scratching can cause false results and make it impossible to read the reactions accurately.
  • Ask patient to bring back own samples to all appointments- may need to retest, read labels etc. (even if product was not tested)
  • If patches become unbearable, the patient can phone to talk to the nurses or doctor. If concerned ask the patient to take a photo +/- discuss with the registrar/consultant and consider review of the patient if necessary
  • Antihistamines may help ease any discomfort and do not interfere with patch test results.
  • Using a cold ice pack wrapped in a tea towel might help settle the itch. It might also help to lean again a cold metal fridge door or cool glass window.

Videos to watch: Applying patches video

See attachment for patch testing instructions.

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