Positive patch test for mercury possibly from exposure to amalgam.

OBJECTIVES Mercury allergy is a serious health problem. We investigated the relationship between positive patch test for mercury and sources of mercury exposure, indicated by concentrations in biological samples from healthy medical students. METHODS Patch tests for mercury (Hg-PT) were performed on 580 students. For a group of 55 students with a positive Hg-PT result (Hg-PT(+)) and a reference group of 79 students with a negative Hg-PT result (Hg-PT)(-)), mercury concentrations in urine (Hg-u) and hair (Hg-h) were measured. In our search for environmental indicators of mercury exposure, the level of fish intake and mercurochrome usage were determined using a self-administered questionnaire. The oral cavity was investigated and the numbers of decayed teeth filled with amalgam (NA) were counted by dentists. RESULTS For the male Hg-PT(+) group, Hg-u and Hg-h were higher than those of a male reference Hg-PT(-) group; Hg-u values obtained in the early morning and after supper were significantly different. Multiple regression analysis with Hg-u as the objective variable among all students showed that increases in the level of fish intake, mercurochrome usage, and the NA independently increased Hg-u measured in the early morning for both gender groups. NA significantly affected Hg-u. CONCLUSIONS We showed that a higher NA was related to a higher Hg-u measured in the early morning. Therefore, exposure to amalgam may increase Hg-u. It was suggested that Hg-PT(+) might be related to a high Hg-u, and possibly to a high NA.