The problem with testing for mercury is that no test is reliable. This is because mercury can be held in the organs and brain and not show up in blood, hair or urine tests. Andy Cutler though does suggest looking at hair test results focusing on mineral transportation. Mercury deranges mineral transportation. He applies a set of counting rules to aid diagnosis. I think though even these are not a 100% especially if supplementing with minerals. My hair tests did not show up a problem even though i know i am toxic

With regard to your brother, peoples teeth apparantly can give off more vapour than others and individuals can excrete at different rates. So if you are a slow excreter and have a lot of amalgams giving off a lot a vapour then you are likely to have mercury collecting in the body.