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The practical use of thyroid function tests

J M Feldman

    American Family Physician
    |September 1, 1977
    PubMed

    The diagnosis of thyroid disorders can usually be established by two tests: the serum T4 and the resin T3 uptake (RT3U). The T4 test measures both free and bound thyroxine; the RT3U reflects the number of binding sites available on thyroid-binding globulin. The values of these two tests can be used to calculate a free thyroxine index (FTI), which gives an approximation of the free T4 in the serum. Measurement of thyroid-stimulating hormone (TSH) is useful for the diagnosis of hypothyroidism, while the thyrotropin-releasing hormone (TRH) test may facilitate diagnosis of hyperthyroidism.

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