Each dermatologist operates their patch testing clinic in a different way. However if several patients are going to be patch tested in the one clinic, it is useful to make the baseline (the ABS) series ahead of time, to assist the clinic to run in a timely manner.
There are a few different varieties of patches available from a few different manufacturers, and these may be fabric style or water-proof. Most centres will choose one variety or may give patients the option to use waterproof patches.
When numbering the patches, staff at SHI Melbourne, write the number at the bottom of the patch, and on both sides of the patch. This assists the person making the patch, so there is no confusion about what is the top of bottom of the patch, and the number is still visible when the patches are applied to the patient.
Numbering when making patches up
1. There is a very specific way to number and label patches. Patches are essentially made up in a mirror-image manner, so they are made up in the opposite way to what you might think. The numbering of the patch goes on the bottom of the patch, for those new to patch testing it can be useful to number both sides to save confusion.
Start here when applying allergens to the patch and work downwards until number 5. Then start at the top again at number 6 and work down until number 10.
Numbering of patches when applied to the patient
2. When the patches are applied to the patient’s back the number will flip over and it will be reversed or become a mirror image of when the patch was made up (or sitting in the transport container if using CABA):
A complete Australian Baseline Series (ABS) positioned on tray. This one has the patches laid out in rows.
Applying allergens to patches
When someone begins to patch test, learning to hold the allergen syringe comfortably can be tricky. The syringe must be held in a way that allows sufficient amounts of the allergen to be extracted, without putting too much on the patch (as soft allergens have a tendency to ‘shoot’ out of the syringe and overflow the patch.)
Below is an image of the best way to hold the hold the syringe; however this may vary from individual to individual. This method also allows for a speedy application method when making up multiple patches.
|When holding the syringe it is best if you put a piece of gauze in your left hand (if you are right-handed, but if you are left-handed reverse these instructions) to pull the cap off and hold (so you don’t contaminate your fingers with any allergen). Use your right hand to apply allergens to the chamber/disc on the patch. Apply the allergen; replace cap, and the return to tray. Ensure you place the allergen back in its correct numerical order in the tray (if applicable).
When making patches you only need to apply a small amount of allergen on the disc (approx. 2mm, or one side of the disc to the other).
|Example of appropriate amount of petrolatum allergen to be applied
If too much petrolatum-based allergen shoots out of a syringe, wipe the excess off with a wooden stick. An excess amount of allergen can be problematic, particularly with textile dyes, as they can leak through the patches, potentially staining clothes, bedding, furniture, meaning you may end up with an unhappy patient, as dyes do not wash out.
|Example of when too much allergen (textile dye) is applied to patches
One thing to remember is when you have finished applying an allergen to the patch chamber; draw back slightly, to stop the allergen oozing out the end. However, it is important not to pull too much air into the syringe, as air in the syringe can cause oxidisation of the allergen (meaning the allergen makeup can be altered).
Applying liquid allergens to the patch:
The majority of allergens are petrolatum based, however there are a few that are alcohol based, therefore are in liquid form. Approximately 2 drops are required to ensure the paper disc is sufficiently wet. If too much has gone on to the patch, use a piece of gauze to mop up any liquid excess. If too much is on the patch it may drip on to other patches when the patch is being applied.
If too much allergen comes out, use a little wooden stick to remove excess allergen.
When new to the area of patch testing, staff may find it useful to write or put a mark on the patch where a liquid needs to be applied. The liquid allergen is usually applied just before patches are applied, so they don’t dry out too much before being applied.
Videos to watch: