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Thyroid Function Testing: A Brief Update

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

Slide 12

April 2009

The next scenario is follow-up of patients. There are many more patients with established thyroid disease then with newly diagnosed thyroid disease, and many of them require life-long or, at least, long-term follow up. For those conditions which are acute or subacute, for example, Graves’ disease or subacute thyroiditis, it is important to measure FT4 because the changes in thyroid hormones can occur, particularly under treatment intervention, very rapidly and the TSH levels may lag a few days or even weeks behind. This can be observed particularly if the thyrotoxicosis has been long standing. In those cases, there is actual atrophy in the pituitary gland of thyrotrope cells, and it can take some weeks for TSH secretion to recover. In most cases, the FT4 measurement is, therefore, the best guide to therapy and resolution of Graves’ disease or subacute thyroiditis. But, it is usually also supplemented with TSH measurements and we have already mentioned that in those rare cases where primarily T3 is secreted, a total T3 measurement can be useful. Chronic or slowly progressive conditions are a little different. Those primarily consist of permanent hyperthyroidism or toxic nodular goiter, where there is either no progression in the disease or very slow progression and, here, the TSH measurement is the main stay, which is occasionally supplemented by FT4 measurements and, rarely, by total T3 measurements.

What Test to Use When, cont.


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