I had 12 amalgam fillings replaced two and a half years ago after a period of physical and psychological ill health. I had a DMSA challenge test for mercury which tests the urine. This showed up extremely high levels of mercury and then i went on to have the fillings replaced. Even though my dentist followed the huggins protocol if felt very ill after the removal and continued to so for about a year which help confirm things further. I also can also only tolerate DMSA at very low doses and cant really tolerate lipoic acid at all (if you do not have a mercury problem apparently these agents should not be a problem tp take). All this confirmed the diagnosis for me.

No test for mercury is conclusive. The problem being that mercury can apparently remain locked in the organs and brain but not be present in urine and blood. So if you get a negative blood, urine or hair test is does not necessarily mean that you dont have mercury in your system doing damage. Challenge tests such as the one i did have also been reported to be potentially bad for you because it can redistribute a mercury around your body causing further damage.
Andy cutler in his book amalgam illness : diagnosis and treatment describes a check list of things to look at when deciding whether mercury might be a problem or not.