We are one of a shrinking band of sites that uses total T4 (plusTSH)
as our front line thyroid screen. Our initial study of moving to
free T4 (plus TSH) suggests:
1. We will have just the same percentage of anomalous results (thatis
abnormal free T4 with normal TSH) as at present - just on different patients.
2. The reference range for free T4 quoted by the manufacturer does not
agree with our findings especially with regard to the lower level of "normal"
3. There is little clinical gain from changing.
(we usually know if patients are on oestrogen and can measure thyroid binding
globulin if in doubt- its not clear to me what is useful if there is is
abnormal free T4 with normal TSH)
Any comments and especially info of the free T4 reference range you use (adult
ambulant) woild be of help. Ours is currently 10-25pmols/L - ACS180 (sorry I am not sure what that
I am not sure what that is in "old money" for our North American readers)
James Falconer Smith
PS comments from sites that have made this change would be especially interesting
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