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Thyroid Function Testing: A Brief Update



Targets for Assessment of Thyroid Function

Slide 4

April 2009

Consequently, all of those 3: TSH, T4, and T3, are the prime hormones for assessment of thyroid function. Let’s cover them one by one. Thyroid-stimulating hormone, TSH, has many reliable assays. They are all of them, today, very reliable with a wide dynamic range. It provides an integrated measure of thyroid hormone action, being the target of the feedback inhibition; it really gives the measure of the tissue affect of thyroid hormone. Furthermore, and we will enlarge this further down in this presentation a little, the response of TSH to changing thyroid hormone levels is greatly amplified, making it exquisitely sensitive to changes in thyroid hormone levels. Finally, another plus is, it’s not affected by any binding protein changes. There are, of course, also a few minuses. First of all, it’s obviously an indirect measure of thyroid function, as it measures the response to rising or falling thyroid hormone levels. So, there is some delay in responses to acute changes in peripheral thyroid hormone levels, which in some clinical situations could be a disadvantage. Finally, in a very rare case, this is <1% of cases, where the patient might have pituitary or hypothalamic disease, or thyroid hormone resistance, or some other exotic disorder, the TSH measurement alone can be misleading.

Targets for Assessment

 


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