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."
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.