Mercury doesn't actually need to show up in a hair analysis test to confirm toxicity...though it did show up in my first test as 0.24 (ref range 0.18, high range 0.36 and above). In my more recent test it didnt show up at all. Hair tests only reveal what is circulating, not what's in the tissues/organs where mercury hides, unless you've had recent exposure, just had your Amalgams out or are in the middle of chelating.
You have to look at the nutrient minerals to see what is going on. I had/have very low potassium and sodium. Low pot and sod together with high cal and mag can also be indicative of merc toxicity. If your minerals are very skewed, ie lots of highs and lows then this can be an indicator of heavy metal poisoning. A healthy person wouldn't have a lot of skewed minerals. A mercury toxic person can high a very high reading, or no mercury reading at all. They might also have high copper or high nickel....everyone is different.
Also if the nutrient minerals follow the 'all low counting rules' as Cutler describes ie if you have low levels of all your minerals (see website below).
Of course you wouldn't just rely on a hair test, you look at symptoms, history etc.
For me, I have very bad reactions to chlorella and garlic and other things like l-cysteine. I also had a surprising reaction to a supplement with a lot of alpha lipoic acid in it last Autumn. I didn't know it chelated mercury, and for a short while my 'adrenal' problems disappeared! However, it didn't stay that way!
Cutler has done a lot of research into mercury, I don't know whether everything he says is true or not, but some of what he says completely fits in with my experience (his website is www.noamalgam.com).
P.S. I had my hair test done via Mineral Check in Kent. It was sent off to Trace Elements Inc, in the States.