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Thyroid Function Testing: A Brief Update

Balancing It All Up - What Test to Use When, cont.

Slide 15

April 2009

Thyroid hormone-binding protein measurements are also useful in some situations, particularly if there are inconsistent thyroid hormone test results between the 3 tests we’ve mentioned before. They can occur in some situations where they are inherited or acquired abnormalities in binding proteins, sometimes related to drug treatment and sometimes related to congenital genetic conditions. The hallmark is that there is large discrepancies between free and total hormone levels, and those type of results should really tip one off that one might want to do a thyroid hormone-binding protein measurements, either TBG concentration measurements or TBG-binding capacity measurements. Finally, there are very, very rare cases where molecular analysis of the thyroid hormone receptors are useful. Those would be scenarios where free T4, total T4, and total T3 are elevated, and TSH level is normal, without there being an acute illness or interfering drug treatment, which could cause this. Those patients may have inherited disorders of the thyroid hormone receptor, so-called thyroid hormone resistance, or some of these patients may have a TSH-secreting pituitary tumor.

What Test to Use When, cont.


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