There is no test to show the mercury levels in the organs other than biopsies. No one would want a biopsy of the brain or other major organs like the liver of kidneys unless it was absolutely necessary. Mercury toxicity is best diagnosed by symptoms, and reaction to chelating agents such as DMSA or ALA when used properly doing the Cutler protocol. Chalenge tests might make some people very sick. They also don't show how much mercury is in the body, just how much is excreted.