This article is from the Amalgam-Related Illness FAQ, by Leif Hedegard.
As stated above (see sections 3.1-3.2.1): if there is a (non-allergic-) amalgam-related illness, it seems, at least on a group level in people who suspect they have such a disease, to be based upon an increased individual (non-allergic-) sensitivity towards mercury / amalgam rather than raised mercury in certain body-fluids. And there are no commonly approved ways of testing this potential (non-allergic-) over-sensitivity (other than provocation - see below).
If you, however, suspect that you have raised mercury exposure you can monitor, roughly, the ONGOING exposure. The diagnosis of (non-allergic-) amalgam-related illness will have to be a probability diagnosis based upon your history, your symptoms, other findings (not common) and of course exclusion of other diseases.
It is not possible to determine Hg-levels in brains / Central Nervous System (CNS) of living, non-occupationally exposed, individuals. However you can measure the mercury levels in body-fluids, faeces and hair. After chronic inorganic mercury exposure mercury half-time (T1/2) for part of the Hg in the brain is years (Berlin in: Friberg 1986, page 399), while for body fluids, faeces and hair the T1/2 are weeks-months. Therefore there are no way that you can determine accumulated exposure, exposure that has ceased months / years ago or mercury levels in brain, by measuring Hg in body fluids, faeces or hair. The total (that is: inorganic and organic) mercury levels in urine and blood-plasma or inorganic mercury in whole blood will, however, give you a rough measure of ongoing (last days-months) inorganic mercury exposure. The total mercury levels in whole blood and hair will give you a rough measure of ongoing exposure to organic mercury (as methylmercury from fish). The clinical usefulness of measuring mercury levels in faeces as well as in liquor cerebro-spinalis depends upon the possibilities to interpret these values, however, not many scientific studies have been published regarding mercury in faeces and liquor cerebro-spinalis.
Half-time (T1/2); the time it takes before a (mercury-) level has decreased to half. Three quotations about this follows here:
See your physician for a medical check up. He / she might find something else than Hg-intoxication that could be treated and could explain part of or all of your symptom flora. For example hypo- / hyperthyreos, Sjogrens syndrome... can mimic Hg-intoxication. It is another question if these and other diseases could be caused by or could be aggravated by mercury / amalgam. Your dentist could maybe find some treatable tempo-mandibular disorder... causing headache...
Write down a life-graph with its ups and downs (symptoms), then get your hands on all your dental journals. Then compare; if there is a connection backwards in time (before you started thinking about amalgam-related illness) between amalgam work in your mouth and your symptoms then an amalgam-related illness could be suspected.
Provocation can be done by removing an amalgam filling. Write down your symptoms a month before and then a month after you have an amalgam-filling removed and compare. This way is less informative because you can always suspect that you out of expectation (placebo effect) will get worse after the filling is removed. Nevertheless, if your symptoms do not increase in severity the month immediately after the removal of an amalgam filling you may suspect that you are not suffering from an amalgam-related illness. Tandvardsskadeforbundet (1993) writes that an adverse reaction "may not take place, if the dentist is extremely careful and provides good protective measures.
Also make sure to read these books: Poison in Your Teeth: Mercury Amalgam (Silver) Fillings...Hazardous to Your Health! and Mercury Detoxification by Tom McGuire