Blood levels are generally only good for recent exposure rather than chronic body burden, and the process is painful and expensive. Stool testing is not very reliable and the sample collection is rather distasteful to most patients. Hair analysis also is best for recent exposures mainly, and can be dangerously inaccurate due to genetic factors.
A 'provoked' urine collection is the best way to test for chronic body burden of toxic metals. The patient is given a dose (oral or IV) of a 'chelator' substance that pulls the toxic (and usually some beneficial ones too) metals out of tissues into the blood stream. The patient then drinks a good amount of water and collects their urine for about 6 hours, sending a sample of it to the lab for analysis.
