The TSH is produced by the pituitary in response to TRH from
yet another gland.  If either of these glands is "off" then the TSH number
may not be meaningful.  When this condition occurs it is called "central"
<whatever: hypo-, hyper-&c> because the problem is not the thyroid
but rather it's overseers.  

Consider an analogy -- your thermostat tells your furnace when to turn on
and when to turn off.  If you went into the thermostat and bent the
bimetallic temperature sensor spring -- guess what?  Your house would
be several degrees hotter or cooler than the thermostat was set for.
So do you pay any attention to the thermostat number then?  Or do you
adjust things so the house FEELS comfortable?  How would you
feel about a repairman who read your thermostat through a microscope
and told you it was set for 71.0003 degrees, and so you didn't need
to worry.  That any cold you were feeling was "all in your head".  Would
you ever call that repairman again?  

A doctor who gives an ultra-sensitive TSH test w/o checking that the TSH
numbers are meaningful is a lot like that fictitious repairman.

TSH numbers may or may not be valid.  Lots of MDs think the
"central" things are very rare -- so apparently they never (or rarely)
test for them.  I sometimes wonder if they are rarely seen only because
they are rarely tested for.  
--
Kevin G. Rhoads, Ph.D. (Linearity is a convenient fiction.)
T_Rhoads@NO_SPAM.MSN.com
krhoads@NO_SPAM.cmpnetmail.com