Atopy Patch Testing (APT)

Atopy patch testing (APT) is done to diagnose non-IgE, or delayed reaction, allergies.  Many allergists don't do this test, or even believe that it works.

According to the most recent AGA paper on eosinophilic disorders:

• "APT has been most extensively studied in atopic dermatitis. Most studies find that APT was better in identifying late reactions and GI reactions in children with atopic dermatitis."
• "...APT has shown promise in atopic dermatitis with good predictive values, high specificity, and low sensitivity, and APT has shown highly promising results with regard to food elimination diet and food reintroduction in patients with EE."
• "APT has been used for the diagnosis of food allergies in two published studies by Spergel et al. They examined 146 children with biopsy specimen-diagnosed EE and eliminated foods based on positive skin test and atopy patch test. The authors found that 77% of the patients had resolution of their biopsy specimens based on these results."

Basically, by using APT in conjunction with SPT (skin prick testing), greater improvements were seen in kids with eosinophilic disorders (and kids with food allergies and/or eczema.)

We searched and searched, and finally found a local doctor that does patch testing and regularly works with eos kids.   Here's how it works:

• First, foods are crushed up and made into a thick paste that will stick on the skin (and not dry out.)  Some doctors use food extracts, but from what I've read the accuracy is much higher when using real, fresh food.
• The foods are placed into small round or square disks that will be applied to the back for 48 hours, and taped into place.  The doctor carefully marks where each section is, so that they are easy to identify when the tape is removed. 

• After 48 hours, the patches are removed.  Some doctors will read the results 20 minutes after removal, but it's really hard to see much at that point since the skin is usually still red from the tape.
• Here is DD about 5-6 hours after removal.  It's getting much easier to see the spots that she's reacting to (which is almost all of them!)  Negatives should be skin colored, positives will be red and possibly blistered or have hives.  (Our allergist made sure to do skin testing first, because applying an IgE allergen to the skin for 48 hours would result in a massive and unpleasant reaction.  So they only test foods that are negative on the SPT.) 

• 24 hours after removal, the patches are read.  You can see that by this point, many of the spots on DD's back had faded, but some are still obviously positive.  The positive spots were still red, and most were bubbly and irritated and starting to scab over.

Skin prick testing (SPT)

I wanted to share some photos of a couple SPTs that DD had, in case anyone is curious what the test looks like.

First, here is a good website describing the process. When you get a skin prick test, you look for a wheal (hive) and flare (red blotch surrounding the hive) to determine a positive or negative. Normally you are given one prick containing histamine for a positive control, and a negative control spot containing nothing (saline, perhaps?) If the other test spots are the same size or larger than the histamine control, you have a positive result. The link above also compares the wheal size to the old class scale that some allergists use (4+ being the most severe allergy.)

So here in the pictures, you can see how they mark each area to be "pricked" with a pen. This particular allergist has a tool that can hold 8 needles at once, so they label each group of pricks with a number. Then the allergens are applied to the skin and a needle pricks or scratches the spot (sometimes this is done all in one step) and you sit and wait anwhere from 5-20 minutes. Here, DD has just had the pricks done, and she is already showing some reactions. The upper spots are just red from being poked, but few are actually positive results. The lower ones however, are definitely positive.



On the bottom right corner in this picture you can see the positive(+) and negative(-) control spots. Just above those (if you're curious) is goat's milk, and you can see that it's quite a bit larger than the positive control, so it's a very clear positive (allergic) result, as are the ones on the lower left.


Just to give another example, here is a SPT from a couple years ago. On the right-hand side, we have 3 positive results. The top and bottom one have very large wheals with just slightly larger flares, and the middle has a smaller wheal with a large flare.

Allergy testing

There are a lot of different ways to test for allergies. Most conventional allergists will only use the RAST or skin prick/skin patch test, which will only show IgE allergies (see Types of Allergies). There are alternative tests which you can get through a natural practitioner, like an ND, or sometimes directly through the lab that does the test. Two of these are the ELISA and the ALCAT. There is also testing which is considered more alternative- such as muscle-testing (kinesiology) and pendulum/crystal testing. I will try to give a brief description of each test. But before trying any of these tests, you should keep in mind that NONE are 100% accurate. Some are better than others, depending on the type of allergy you have.

RAST (radioallergosorbert test) - this is a blood test usually done by an allergist. Your blood is drawn and tested; no allergens are placed in/on your body. This test measures the amount of IgE that reacts with a specific allergen. An allergist will choose which foods or environmental allergens are tested. Good for people with eczema or reactive skin as opposed to skin tests. Good for environmental allergies, or IgE food allergies. Not very accurate for babies.

Skin tests - There are a few different types, but the most common is the skin prick test. The skin is scratched with a little needle, then an allergen is rubbed onto the scratch. The amount of swelling on and around the spot is measured to show an allergic reaction. This test also shows only IgE allergies; it will NOT show food intolerances. Not very accurate for babies.

Patch testing - I haven't actually been able to locate a doctor who uses this test, but I'm told that some do. From my understanding, allergens are placed on discs which are taped to the body and left for a period of time (48 hours?) then checked for swelling and redness. This test is said to work for both IgE and IgG allergies.

ELISA (enzyme-linked immunosorbert assay) - This is a blood test done to check for delayed-reaction allergies or intolerances. Most will NOT show IgE allergies, although some labs do a combined IgG and IgE. There are many varieties of this test, and just like all the others it is not 100% accurate. Can usually test for hundreds of foods with one blood draw. Accurate (or so I'm told) on babies of any age.

ALCAT - This is another blood test that is for finding delayed-reaction allergies; will NOT show IgE allergies. Measures leukocyte cellular reactivity in whole blood. There is some debate as to whether you need previous exposure to a food before it will show up on the test accurately. This is one of the few tests we didn't try, so I'm not as familiar with how it all works.

Muscle testing (applied kinesiology) - This test is done by alternative practitioners, and is used for many things besides allergies. The basic idea of this is that you can hold a food or chemical in your hand, the practitioner will press down on your arms and determine whether the arm holding the substance is weaker- indicating that it is unhealthy for your body. We have also not used this test, so I welcome comments or additional information about it.

Crystal/pendulum testing - This test is easy to do yourself (and free!). It involves placing the questionable substance in one hand, holding your pendulum over that wrist, and watching the direction or pattern of how it swings. The results are not the same for everyone- you have to test your crystal/pendulum to see what means "yes" and what means "no" for you personally. If you get a "no" reading, then you know that substance is not healthy for you. Here's a cool video of crystal testing in action.