There are several options for heavy metal testing.
Blood: An elevated level of a heavy metal in the blood means there has been a recent exposure or there is an ongoing exposure. Heavy metals are not tolerated in the blood for long periods. They are moved out of the blood and sequestered in the tissues.
Hair: This is the least invasive, the least expensive and the least accurate. It's a good screening tool. If the metals are high in the hair and it's not due to hair products then there is high probability of high levels in the tissues. However, if the hair comes back negative for metals the metals may still be present in the tissues but not being excreted in the hair.
Stool: This will give you an idea of how much metal the liver is processing from the blood and attempting to excrete through the bile on a daily basis. If the patient has a compromised intestinal lining they may reabsorb some of the metals, toxins, hormones and other materials the liver is excreting. Therefore sometimes this result appears lower than the actual amounts in the blood. This test, like the blood, only gives you an idea of the levels of metals in the blood, not what is stored in the tissues.
Urine: This also gives you an idea of how much is circulating in the blood. The kidneys filter out some of the metals and excrete them in the urine.
Provoked Urine (or stool) Collection: This is the preferred and most accurate method of estimating the toxic burden of heavy metals in the tissues. The patient takes a oral or IV loading dose of a chelating (metal binding) substance, typically DMSA, DMPS or EDTA. I use DMSA since it can be administered orally. The chelating substance is absorbed into the tissues and binds preferentially to heavy metals and is then eliminated through the urine. The urine is collected over 6 hours and measured for metals.