Patch allergy testing is a fairly accurate way of finding out which substances you are allergic to, especially if you are concerned about contact dermatitis. The test involves coating a skin patch with the extract of a particular allergen and sticking the patch on your arm or back. Unlike a scratch test however, you will need to wait at least 48 hours before you are able to determine test results. Some allergic reactions are delayed and may take a day or two to form.
Most people don’t have to make any special preparations prior to patch allergy testing, but people who take certain medications should stop taking them. If you are taking prescription or OTC antihistamines, tricyclic antidepressants or heartburn medication, you should stop taking these at least 10 days prior to your allergy test. These medicines are known to interfere with the results of a patch test.
If you cannot stop taking your medication for any reason, you should let your physician know immediately. A qualified allergist can run several tests to determine if your medication will have an adverse effect on your test results.
Ideally, you will be tested for most, if not all, the allergens your chosen allergy testing center carries. However, your physician may prioritize certain allergens that you are likely to have a reaction to, based on your family’s medical history. These patches will be left on for about 48 hours. It is advised that you do not get these patches wet as the water may affect the results of your test.
If your allergy skin test proves you are allergic to a particular substance, you may notice a mosquito bite-like bump at the site of the patch. The size of these bumps often indicates how severe your body’s reaction is to a specific allergen. Your doctor will take note of all reactions, including the possibility of any false positive or false negative reactions. Afterwards, your doctor will discuss any necessary changes needed to avoid the allergens your body reacts to.