Importance of patch testing with patients’ own samples
When patch testing, we recommend you test patients to samples of their own products, in addition to commercially available allergens. The reason for this is that the commercially available allergens will only detect between 70-80% of cases of allergic contact dermatitis. This is not ideal especially if occupational issues are being investigated. In spite of patch testing with commercially available allergens, the responsible allergen may remain elusive unless patch testing with the patient’s own sample is undertaken. Products that the patient uses at home, and at work (if relevant) should be considered for testing.
Patch testing with patients’ own products is recommended because:
- It helps to confirm the actual cause (the causative allergen) and testing with own samples may also assist to prove causality in medico-legal cases.
- Sometimes testing to patients’ own sample is the only clue to diagnosis, leading to the identification of the cause of the contact dermatitis.
- Testing to own products also assists in detecting rare or new emerging allergens, and also reflects actual exposures in the workplace.
- Sometimes on testing, a patient may not react to individual ingredients, but may react to a complete product. This is known as compound allergy.
A reference book we would recommend for people patch testing is:
De Groot, Anton C. (2008). Patch Testing. Test Concentrations and Vehicles for 4350 Chemicals (3rd edition), Wapserveen, the Netherlands: acdegroot publishing (available from www.patchtesting.info).
This book provides information about the recommended patch test concentrations and vehicles for a large selection of chemicals, which is required when testing patients’ own samples or products from their workplace.
Work undertaken by our organization has suggested that people working in certain industries significantly benefit from being patch tested to their own samples. These include people working as machine operators, tradesmen and health care workers. We have published an article about the importance of patch testing to own samples (referenced below):
Slodownik D, Williams J, Frowen K, Palmer A, Matheson M and Nixon R. ‘The additive value of patch testing with patients’ own products at an occupational dermatology clinic.’ Contact Dermatitis 2009: 61: 231-235.