Thyroid function tests
Adequate clinical information, including a drug history is
essential in order to provide information of most value in the
diagnosis and management of thyroid disorders.
The first line investigation is freeT4 and
Further tests, including free T3, will be performed as
considered appropriate. Generally free T3 is always elevated if FT4
is elevated and so its measurement is unnecessary.
Free T3 is added to detect T3 toxicosis when FT4 is normal but
the TSH is below normal and to monitor T3 toxicosis and to monitor
thyroid function in patients on Amiodarone. Otherwise it will not
be measured unless there is some other complicating factor that has
been discussed with the duty biochemist.
Other assays such as free hormone investigations and TBG are
sometimes helpful but not usually necessary. The use of these
assays and any interpretative problems can be discussed with the