Patch testing with amalgam at various concentrations.

27 patients with positive D3 reactions on patch testing to 3 mercury screening allergens were patch tested with 13 mercury patch test preparations, 6 inorganic and 7 organic, and amalgam 20% pet. The 13 patients (all women) showing positive reactions to 20% amalgam were then patch tested to reducing concentrations. 2 patients reacted down to 1%, 4 down to 2%, 4 down to 5%, 2 down to 10% and 1 only to 20%, a total of 10 of the 13 patients therefore reacting to the 5% concentration of amalgam. The appropriate patch test concentration of amalgam is discussed and the clinical significance and female preponderance of amalgam reactivity suggested as being worthy of further investigation.