Patch Testing with Metal Allergens
The standard allergen series used in patch testing contains metals that most commonly cause allergic contact dermatitis, but testing with additional metal allergens is warranted for selected patients.

Patch testing is most commonly performed for patients with oral disease (almost half the patients), patients ready to get a tooth fill, intracoronary stents, hip and knee prostheses, as well as other implants, patients getting some sutures in their joints, hand dermatitis, generalized dermatitis, and dermatitis affecting the lips, legs, arms, trunk, or face. Metals with the highest allergic patch‐test reaction rates are nickel, gold, manganese, palladium, cobalt, Ticonium, mercury, beryllium, chromium, and silver.

Metals are ubiquitous, and some metals (eg, nickel) are well recognized as a common cause of allergic contact dermatitis.

Among dermatitis patients, the prevalence of metal allergy is even higher.

Environmental metal exposures include jewelry, buttons, clothing fasteners, dental restorations, mobile phones, and leather. Although consumer exposure is responsible for most cases of metal allergy, the importance of occupational metal exposure remains present and should always be taken into consideration when one interprets allergic patch test reactions to metals. Traditionally, nickel, cobalt, and chromium have been the most important contact allergens. However, recently, gold and palladium have drawn much attention as the prevalence of contact allergy to these metals is high. Palladium allergy is mainly a result of cross-sensitization to nickel, whereas gold allergy is rarely clinically relevant when one takes its high prevalence into account. In the United States, the prevalence of nickel allergy is quite high. The prevalence of chromium allergy is increasing in the United States, Singapore, and Denmark among dermatitis patients. This increase is significantly associated with leather exposure in Denmark. Metal allergy may result in allergic contact dermatitis and systemic allergic (contact) dermatitis. Furthermore, metal allergy has been associated with device failure following insertion of intracoronary stents, hip and knee prostheses, as well as other implants. The annual number of total knee replacement implantations is rising continuously. A progressive cutaneous hypersensitivity rate against metallic materials can lead to an increase of allergy-induced reactions associated with implant loosening in the future. On apparent allergy against metallic implant components different alternative solutions to standard endoprostheses should be taken into account for primary implantation or revision of total knee replacement, for example the application of implant components without metallic elements (e.g. ceramics), the use of non-allergic metallic implants, such as titanium or ZrNb alloys, or potential allergy-inducing metallic materials after masking the implant surface using a suitable coating. In the case of primary or revision surgery most patients with metal allergy are treated with a Ti(Nb)N-coated knee implant made of cobalt-chrome or titanium alloys.

Patch testing

During a patch test, very small quantities of potential allergens are applied to your skin and covered with small patches. The patches remain on your skin for two days before the doctor removes them. If you have a nickel allergy, the skin under the nickel patch will be inflamed when the patch is removed or in the days after removal of the patch.

Because of the low concentrations of allergens used, patch tests are safe even for people with severe allergies.

Patch tests (contact allergy testing)

Dermatologists apply patch tests in patients with dermatitis, to find out whether their skin condition may be caused or aggravated by a contact allergy. Patch tests are not the same as skin prick tests, which are used to diagnose hay fever allergy (house dust mite, grass pollens and cat dander). Skin prick tests have very limited value for patients with skin rashes.

The appointments

The first appointment will take about half an hour. Tiny quantities of 25 to 150 materials in individual square plastic or round aluminium chambers are applied to the upper back. They are kept in place with special hypoallergenic adhesive tape. The patches stay in place undisturbed for 48 hours.

At the second appointment, usually two days later, the patches will be removed. The back is marked with an indelible black felt tip pen or other suitable marker to identify the test sites.

These marks must still be visible at the third appointment, at 72 hours. The back should be checked and if necessary remarked on several occasions between the 2nd and 3rd appointments.

The results

The dermatologist will complete a record form at the second and third appointments (usually 48 and 72 hour readings). The result for each test site is recorded. The system we use is as follows:

• Negative (-)
• Irritant reaction (IR)
• Equivocal / uncertain (+/-)
• Weak positive (+)
• Strong positive (++)
• Extreme reaction (+++)

Notes

• Wear old clothing; felt tip pen marks can stain clothes
• Do not swim, rub, or exercise, as the patches may come off
• Keep the back dry, so no baths, showers or sweating
• Avoid exposure to sun