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Thyroid Function Testing: A Brief Update

Targets for Assessment of Thyroid Function

Slide 8

April 2009

Free T3 has the same advantages, more or less, as free T4 and very similar disadvantages. One of the major disadvantages here is that all current free T3 assays have serious shortcomings and generally are not recommended. They are too unreliable in medical clinical situations. The limitations are caused, by and large, the very large low concentrations of the analyte which is being measured. Free thyroxine concentrations are already only a few percent of the total thyroxin concentrations. Free T3 concentrations, in turn, are only a few percent of the total T3 concentrations, and the total T3 concentrations are never more then 20% of the total thyroxin concentration. So, we are talking about low picomolar concentrations, which causes a lot of analytical problems.

Targets for Assessment


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