What do TSH levels and free hormone levels indicate in hypothyroidism diagnoses?

Updated: Mar 03, 2021
  • Author: Philip R Orlander, MD, FACP; Chief Editor: George T Griffing, MD  more...
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Patients with primary hypothyroidism have elevated TSH levels and decreased free hormone levels. Patients with elevated TSH levels (usually 4.5-10.0 mIU/L) but normal free hormone levels or estimates are considered to have mild, or subclinical, hypothyroidism.

Primary hypothyroidism is virtually the only disease that is characterized by sustained rises in TSH levels. As the TSH level increases early in the disease, conversion of T4 to T3 increases, maintaining T3 levels. In early hypothyroidism, TSH levels are elevated, T4 levels are normal to low, and T3 levels are normal. Given this early protection of the T3 level, routine checking of T3 is not recommended if one suspects that a patient is hypothyroid. Drawing a reverse T3 is also not recommended as a routine part of the hypothyroidism workup.

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