About patch testing
We use patch testing to identify various types of delayed drug allergy, including penicillin. These are allergies which happen more than 6 hours after taking a drug.
We perform patch testing after your child has had a negative skin prick test for immediate allergy. (A negative skin prick test means your child is unlikely to have an immediate allergy).
Patch testing is not painful, but if there is a reaction, your child's skin may become itchy or sore.
If your child becomes distressed because of the patch, you can remove it. If this happens, contact us to let us know.
Patch testing on its own is not 100% accurate. However, when we combine it with a follow-up test by mouth (see Follow-up, below), it gives us an accurate result for penicillin allergy.
What happens during the test
You can expect the following during the test:
- To make the patch, we place a small amount of amoxicillin on a paper disc, inside a small metal chamber. Amoxicillin is a type of penicillin antibiotic. The chamber looks like a small metal disc and it measures about 1.5 cm across.
- We place a control patch (which uses salty water instead of amoxicillin) next to the amoxicillin in the chamber. We use this control to check if your child's skin reacts by having something neutral against it.
- We use hypoallergenic tape to fix the chamber to your child's back.
- We write some markings on your child's skin, next to the patch.
Important
Your child must wear the patch continuously for 48 hours.
Do not try to remove it or reposition it.
They must not bathe, shower or swim during this time, to avoid disrupting the test.
Recording test results
After your child has worn the patch for 48 hours, use your phone to photograph their skin, then remove the patch and photograph their skin again.
Follow the example timeline below to take the necessary photos of your child's skin.
Example of timeline
| Day 1 (eg Monday) | We apply the patch. Your child must wear it for 48 hours. |
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Day 3 (eg Wednesday)
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When your child has been wearing the patch for 48 hours, you must:
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| Day 5 (eg Friday) |
48 hours after you remove the patch, you must:
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If your child's skin appears red on day 5, we will ask you to take another photo two days later (on day 7).
Follow-up
When we receive your photos, we will look at them.
If the patch test is negative, we will ask you to bring your child to Kingston Hospital Dolphin Ward.
We will give them a single dose of amoxicillin orally (by mouth) while under observation. This takes no longer than 1 hour.
Contact information
Kingston Hospital Paediatric Admin team
Telephone:
020 8934 6403