Patient own samples and dilutions
When patch testing, it is recommended that patients are tested to their own product samples, in addition to commercially available allergens. The reason for this is that the commercially available allergens will detect between 70-80% of cases of allergic contact dermatitis, therefore there is potential for the responsible allergen remaining unknown and undiagnosed in 20-30% of cases (REFERENCE). This is not ideal, especially if occupational issues are being investigated.
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 medicolegal 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 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.
Work undertaken by our organisation has suggested that some people working in some 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:
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.
As part of the patch testing process, patients are asked to bring in products they are using from work and home. An article published by the group at ODREC shows the importance of testing patients’ own products11. These products may include shampoo, makeup, hand wash, gloves, moisturisers and hair dye, along with work chemicals such as epoxy resins, to name a few.
Many products need to be diluted, as they are too strong to be tested directly on the skin, and would cause an irritant reaction. This is not a true allergic reaction, and should not be mistaken for one.
The general principle for determining when a product should be diluted is:
- If it is usually mixed with water and only stays on the skin for a short period of time, and rinsed off, then it should be diluted e.g. hand wash.
- If it is used directly on the skin and is left on, such as a moisturising cream, it will not need to be diluted.
Products that are usually diluted include:
- Shampoo and conditioner
- Hand cleansers
- Facial cleansers
- Hair dye
- Work chemicals
The doctor will order the required dilution on the patient’s patch test chart. Some of the more common dilutions can be found in PatchCams©.
What you need when diluting patient products:
How to dilute samples
For water dilution, draw up the required volume of water with an insulin syringe, place in a pill cup and then mix with the required amount of product (use wooden stick applicator) and dab the diluted mixture onto the patch.
Common dilutions when using 1ml syringe of water:
1.0% dilution – a small dot of sample (i.e. one match head size dot) mixed with 1 ml water
10% dilution – about 2 dots of product sample (i.e. 2 match head size dots) mixed with 1ml water
If you need a smaller dilution such as 0.1% or 0.01%, serial dilutions of the 1% solution can be made.
For more liquid-based products, use a 1ml syringe to draw up desired amount of the product.
For oil-based products you will need to use soft white paraffin/Vaseline/petrolatum jelly for dilution instead of water. Use a 10 ml syringe packed with petrolatum, and dispense the volume (mL) required into a mixing cup. Mix well and apply to the patch.
For example, use 1 ml of petrolatum from the syringe, and 2 match stick head size samples of product for a 10% dilution, or only one tiny match stick head size for 1% dilution.
Using a 10ml syringe – fill with petrolatum
Some people may prefer to use a 10 ml syringe for the dilutions.
The doctor will order the required dilution on the patient’s patch test chart. A few common dilutions are:
- Shampoo and conditioner diluted to 1% in water (1 ml water, and one match head size of shampoo or conditioner)
- Hand cleansers 10% in water (1 ml water and approx. 2 match head size drops of hand cleanser)
- Hair dye 10% in petrolatum (1 ml of petrolatum dispensed from 10ml syringe of petrolatum, mixed with 2 match head size of hair dye).
Dilutions chart- A guide
See PatchCams© for the most common dilutions. If you are unsure about what the product is and how it should be diluted, please refer to the following book:
Anton De Groot’s book: Test Concentrations & Vehicles for 4350 Chemicals, Patch Testing 3rd Ed. Acedegroot publishing. Available for purchase from http://www.patchtesting.info/
When patch testing patients own products, it is important to be aware that one item can have several components, for example a glove can have a material and rubber component. Test each part and label on the chart.
|For all patient own products, if you don’t know what it is then don’t test it.
Things that should not be tested:
- Strong cleaning products e.g. toilet cleaner
- Car or floor wax
- Organic solvents
- Metal chips (coarse)
- Rust remover
Many things are irritants and should not be tested. If you don’t have information on the product or are unsure of what the product is – do not test it! Refer to De Groot for more details.
Examples of patient samples
|Examples of removing rubber from hammer handle using a blade.
Stick on to patch using petrolatum
Example of removing outer surface of a face mask
Stick on to patch using petrolatum
|Example of blading a wood sample. Stick on to patch using petrolatum.
|Spray perfume into a cup and use a stick to apply to patch
|Example of glove sample being chopped and applied to patch. Ensure it is the same size, or slightly smaller than the size of the disc
2009 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.
Videos to watch:
- Testing patient samples