The most accurate place to get tested for heavy metals--HMs-- is in the morgue, but that is not so desirable ; )
HMs are a retention toxicity according to Boyd Haley, former chair of the chem dept at the U of KY and others. Lead gets stuck in bone. One type of mercury--Hg--essentially gets stuck in the brain. Therefore it is not so easy to know according to current testing.
Many doctors will order a provoked urine "challenge" test; however that is done with high doses of chelators such as DMPS or DMSA. Some people are very sensitive to chelators and have a very bad experience when given large doses. For example //www.curezone.org/forums/am.asp?i=2255067
Those chelators don't get into the brain, bones and most organs so you don't know what is going on in the places that are most vulnerable to Hg.
Typical blood tests are only sensitive enough to discover high levels from a recent exposure in a chem factory accident, etc.
Hair test might be interesting if the Hg is the organic form from eating too much fish plus Hg in flu and some other vaccines.
Urine Porphrins test is looking for the effects of Hg. It is a bit of a crap shoot because the technician must be very careful with the sample. However if it is positive, you have a decent chance that a doctor will take you seriously.
If you are too sick from Hg to work full time and you are not on a combo of diet, supplements and medication that has been fairly effective in addressing the symptoms, you have a decent chance of having a test that is at least suspicious for one of Cutler's Rules.
Dr Chris Shade is developing a new combination of tests. You could look that up.
Even though Cutler wrote a book on his hair test theory and the use of hair tests, he really relies mostly on symptom clusters for diagnosing Hg. Science has a good feel for how Hg commonly fouls up the body.
So if you have a long list of seemingly unrelated symptoms that your doctors have not had much luck in addressing and those symptoms are consistent with Hg, then it is reasonable to try detox.
The rule of thumb in the yahoo HM detox groups is that getting a fairly typical reaction to taking an Hg chelator further suggests that Hg is involved.
People with an Hg problem typically gets some gains in the first few months. This is yet another indication.
When I was at your stage of the process I was really pissed about the crappy situation of HM testing!
My provoked urine and porphyrins tests were clearly negative. My hair test--#354 -- was barely suspicious for lead and cadmium; however they matched my symptoms quite well and I had a reasonable source of exposure for decades in my family's business. Therefore my doctor offered to write the script for the chelator to give it a try.
After 1.75 yrs of detox I had two followup hair tests with either lead or cadmium in the red and other toxins in the yellow. My bone density and kidney numbers--eGFR--returned to normal and my doctor took me off my last medication. I just remained on supplements and modest dietary modifications. I was lucky to guess correctly. My health is not perfect but certainly improved.
Many people in the detox groups had inconclusive tests but decided to give it a try since their doctors had so little success with other treatments.