By low I mean below suppressed, 0.02 or something like that. Although the trend seems to be to keep the TSH higher and higher, so maybe they could be talking just about below 1. And it doesn't indicate an imminent heart attack or crumbling bones but lots of doctors think it does and use that as an excuse for keeping the TSH too high and the patient ill.
In the beginning - of blood tests - to find out if a patient had a thyroid problem, doctors would test TSH, FT4 and FT3, which all us patients agree are very necessary to get a clear picture - well, as clear as is possible.
For some reason which eludes me, laboratories took over the power of doctors and started refusing to do FT3 tests if the other two were 'in range' - a meaningless statement in itself. And, it would appear, their word was law and they could over-ride the instructions of doctors (not really sure why doctors, who consider themselves god-like, put up with this, but still...). (Actually, I think they only reason they put up with it is because they don't know how to read the other tests anyway.)
Now, it would seem, they are going one step further and refusing to do the FT4 if the TSH is 'in range'. Just what lab technicians know about the thyroid and its malfunction, I cannot say, but it would appear they think they know more than doctors - which admittedly isn't difficult, but still...
Just where all this will end, I really don't know. Perhaps they will start refusing to even test the TSH if there's an R in the month, or if the innards of the chicken they've just slaughtered indicate there is no need. Seems to me that anything is possible...
So, you had an FT4 test - at least, I hope it was an F, because sometimes they do the total and that gives you no useful information whatsoever - and it's good that you got it. But it isn't a given anymore. Unfortunately.