What is a Patch Test?
A Patch test is a patch testing procedure to diagnose allergic contact dermatitis, whereas the diagnosis of irritant contact dermatitis is based on exclusion of an allergic component. Patch test techniques for diagnosing ACD have been used for over 100 years and the present test methods are based on the established principle of using a testing material (chemical, food, etc) and a delivery device (chamber).
What is Patch Testing?
Patch testing attempts to reproduce the allergic reaction on the normal skin on the upper back of the patient. The patches are applied and subsequently removed after 48 hours. Reactions are read after 72-96 hours and often, again at 7 days after removal. The diagnostic value of patch testing depends upon the choice of test substance, the vehicle, the concentration, results interpretation and patient counseling. Patch tests are comprised of materials that occur in the home, work and/or recreational environment.
Patch Testing for Proper Diagnosis of Contact Dermatitis
Appropriate diagnosis and management of persistent eczematous conditions such as contact dermatitis are common challenges for the dermatologist when patch testing. In 2008, the prevalence of contact dermatitis in the general U.S. population was variably estimated between 1.5% and 5.4% and reported to be the third most common reason for patients to seek consultation with a dermatologist, accounting for 9.2 million visits in 2004. It also accounts for 95% of all reported occupational skin diseases.
Contact allergen skin testing is a simple and objective scientific method available to physicians to augment the diagnostic process. Often, the patch test response is the crucial piece of information that allows for the early identification of the offending allergen(s) and confirmation of a diagnosis of Allergic Contact Dermatitis (ACD) and/or Irritant Contact Dermatitis (ICD). Once a diagnosis is achieved, the patient can then take appropriate action to avoid exposure to the allergen and, if possible, substitute non-allergenic agents.
When your provider has referred you for patch testing, you will be set up with 3 different appointments. The first appointment will be with the nurse to apply the patches. You will not be able to take a shower or use any oral steroids during the patch test process. The nurse will then set you up for an appointment for 48 hours later for the removal of patches. At this visit, the nurse will remove the patches and write down any reactions you might be having at that time and schedule you an appointment to see your provider in 48 more hours. At your reading appointment, the provider will take a look at the area where the patches were applied to see if there were any positives. If so, they will provide you with a copy of the allergen with common household allergens to avoid.