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Thyroid Function Testing: A Brief Update



Balancing It All Up - What Test to Use When

Slide 11

April 2009

These recommendations are summarized in this algorithm, which Mayo Medical Laboratories generally recommends for initial workup of nonhospitalized patients with suspected thyroid disease. We can clearly see it’s primarily driven by the initial TSH measurement. If this is below the reference range, then hyperthyroidism can be suspected and can be further confirmed by the free thyroxin measurement. In rare cases, where that is only borderline elevated, or not elevated at all, it could be that this is early Grave’s disease, for example, where primarily total triiodothyronine would be elevated and, hence, a total T3 measurement might be indicated. In situations of borderline thyrotoxicosis the algorithm is very similar. Finally, in the normal range, no further testing is generally justified. Lastly, for those patients with elevated TSH, the diagnosis of hypothyroidism can be suspected if the elevation is minor. This is typically called subclinical hypothyroidism and further supporting factor would be a normal T4. If the T4 or the free T4, in particular, is also slightly depressed and the TSH is >10, which we don’t have in this algorithm, then generally a clinically diagnosis and biochemical diagnosis of manifest hypothyroidism is made. If the etiology of that is in question, then autoantibodies to thyroid tissues can be measured. This can also be helpful in cases of subclinical or borderline hypothyroidism to determine what the risk of the patient is to progress to full-blown hypothyroidism.

What Test to Use When

 


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