Patch Testing With a Large Series of Metal Allergens

Findings From More Than 1,000 Patients in One Decade at Mayo Clinic

Mark D.P. Davis; Michael Z. Wang; James A. Yiannias; James H. Keeling; Suzanne M. Connolly; Donna M. Richardson; Sara A. Farmer


Dermatitis. 2011;22(05):256-271. 

In This Article

Methods and Materials


This retrospective study was approved by the Mayo Clinic Institutional Review Board. Patients were tested at Mayo Clinic (Rochester, MN; Scottsdale AZ; and Jacksonville, FL) from January 1, 2000, through December 31, 2009. Those who underwent patch testing for suspected allergic contact dermatitis from metals were identified from our institution's patch test database. Patients who withheld research authorization were excluded from the study.

Specialized Metal Allergen Series

During the study period, 36 metals were included in the metal series (Table 1). Some of these allergens were the same metal in different concentrations or forms. The metal series has evolved over time, new metals being added (eg, Ticonium [CMP Industries LLC, Albany, NY] and Vitallium [Austenal, Inc., Chicago, IL] were added to the metal series in 2008) and others being removed during the study period, as directed by the Mayo Clinic Dermatitis Group. Therefore, not all patients were tested with an equal number of metal allergens. Because the metal series often is used in the evaluation of patients who may have allergic contact stomatitis from dental fillings, many metals in the series are metals used in the mouth, including those contained in amalgams.

Metals in the Standard Series

The metal series generally is used when patients who are suspected of having allergies to metals are tested; this testing is generally done in conjunction with patch testing with the standard allergen series. The standard series contains six metals commonly associated with allergic patch-test reactions: nickel sulfate hexahydrate 2.5%, gold sodium thiosulfate 0.5%, cobalt chloride 1%, gold sodium thiosulfate 0.25%, gold sodium thiosulfate 2%, and potassium dichromate 0.25%. For this study, we included the data from metals in the standard series. All allergens are in petrolatum unless otherwise stated.

Individual Use Tests

For patients with metal prostheses (eg, stents, amalgams, joints, or screws), we tested with the materials used in the prosthesis itself (in addition to testing with the metal and standard series). Prosthesis-specific test materials generally were supplied by the manufacturers. Similarly, if patch testing was performed for a patient with oral disease suspected of being attributable to an amalgam allergy, we endeavored to identify the amalgam and apply it during the patch test. (Such a patient also would have undergone patch testing with the standard series, an oral flavoring series, and the metal series.) The extensive data from individuals' use tests were not included in this article owing to space constraints.

Patch Testing, Reading and Interpretation, and Clinical Relevance

Patch testing was conducted with a standardized method as previously described.[3,7–12] Patients did not undergo patch testing if topical corticosteroids were applied to patch-test sites, if immunosuppressive medications were taken, or if skin responsiveness was compromised by medical conditions.

All testing was performed with Finn Chambers (Epitest Ltd Oy, Tuusula, Finland) on Scanpor tape (Norgesplaster Aksjeselskap, Vennesla, Norway). Patches were applied to the upper back and were left in place for 48 hours. Sources of allergens are summarized in Table 1. After patch-testing with metal discs, the discs were cleaned, treated with germicidal wipes, and saved for reuse.

Patch-test reactions were read and recorded on day 3 (after the removal of patch-test material), on day 5, and at least once during days 7 through 10. Reactions were interpreted again at least once during days 11 through 17 at Mayo Clinic in Rochester and Florida (but not at Mayo Clinic in Arizona). Patch-test reactions were interpreted by using criteria similar to those of the North American Contact Dermatitis Group.7–11 Possible outcomes were recorded as negative reaction, macular erythema, weak reaction (nonvesicular erythema, infiltration, and possibly papules), strong reaction (edematous or vesicular), extreme reaction (spreading bullous ulcerative lesions), and irritant reaction. A positive patch-test result was defined as a weak, strong, or extreme allergic reaction. As previously described,[13] macular erythema reactions were considered positive if the results were relevant.

At or after the final reading, the physician met with the patient to discuss the relevance of the patch-test results. The relevance of each reaction was recorded as follows: I (irritant); N (allergic, not relevant [no exposure to products containing the allergen]); Q (allergic, questionably relevant [current exposure to products likely to contain the allergen]); P (allergic, formerly relevant [past exposure to products likely to contain the allergen]); and R (allergic, relevant [the result of a use test or patch test with the allergen-containing product is positive, or the ingredient was verified in the patient's product and the use of that product was verified]). For the purposes of this study, relevance was calculated as R + Q.

Statistical Analysis

Patient data were entered into a clinical Sybase database (Sybase Inc., Dublin, CA) using a client server written in Uniface (Compuware Corporation, Detroit, MI). All statistical analyses were performed with SAS software (SAS Institute Inc., Cary, NC).

Associations between patient characteristics and metal sensitivity were assessed with the two-sided chi-square test or the Fisher exact test, as appropriate. A p value of less than .05 indicated a statistically significant difference.


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