Patch Test Panel Comparison
Patch test techniques for diagnosing allergic contact dermatitis have been used for over 100 years and while the tools have changed, the principles remain the same. The present test methods are based on the established principle of using a testing material (chemical, food etc.) and a delivery device (chamber). In this article, we are going to discuss the patch test chambers that are commercially available and the considerations that should be taken into account when purchasing them.
Not all patch test chambers are created equal. They are made of different materials, shapes, sizes, and depths. Even the tape, with which they are applied to the back, differs. There are a variety of commercially available patch test chambers. Although the selection is vast, the majority of offices in North America patch test using the following three brands - Finn Chambers®, allergEAZE®, or IQ Ultra®.
There are 3 basic features that every chamber should have.
- A chamber that provides good occlusion to skin, keeping the allergen from "spilling" out beyond the test site.
- The tape must adhere well to the skin but must be non-irritating.
- All components of the panel must be made of inert materials that do not cause skin reactions.
Over the years, considerable advancements have been made to make patch testing easier. A few examples are the open chamber design, allowing for the loading of allergens without ever exposing the adhesive tape (maximizing occlusion to the skin). The pre-fixed filter paper was included in the chamber to the ease of loading liquid allergens. However, to date, the biggest improvement to patch test chambers happened in early 2013 with the introduction of Finn Chambers AQUA® and allergEAZEclear®. These new chambers are water resistant, allowing patients to participate in moderate exercise or take a light shower while being patch tested. The tape used for these two chambers is a clear polyurethane film coated on one side with a medical grade acrylic adhesive.
Another important consideration is the size and depth of the chambers. The depth of a chamber can vary significantly. This means that dependent upon the chamber used, more allergen may need to be dispensed to ensure proper uptake into the skin. A study conducted by Hamann, Hamann and Hamann (2013) demonstrated that the dose delivered by varied more than 2-fold across the various patch test systems. Examining the different depths of the chambers and the recommended amount of allergen is often overlooked but can have an impact on the results of testing and potentially the cost as well.
Below is a chart that outlines the differences of the various commercially available panels.
Click to view larger
The evolution of patch test panels has meant significant improvements in how the chambers function and their ease of use. Every patch test clinic is unique in their process and needs. Understanding all the options available and determining your office needs will ensure you select the panel best suited to your requirements.