Triiodothyronine, Serum

Metabolic Health

A healthy result should fall into the range 2 - 4.4 pg/mL.

Triiodothyronine (T3) is the most biologically active thyroid hormone in humans. It is sometimes called total triiodothyronine because it includes both free triiodothyronine and triiodothyronine bound to proteins. Triiodothyronine acts on almost every cell in the body, binding to thyroid hormone receptors and setting the metabolic rate of cells. Triiodothyronine is critically important for the growth and development of fetuses, infants, and young children. While the thyroid gland produces triiodothyronine, about 80% is created from the other active thyroid hormone, thyroxine. More than 99% of triiodothyronine is bound to proteins in the serum, the rest is free triiodothyronine (free T3). 

Normal Ranges for Total T3:

  • Adult (> or =20 years): 80-200 ng/dL
  • 0-5 days: 73-288 ng/dL
  • 6 days-2 months: 80-275 ng/dL
  • 3-11 months: 86-265 ng/dL
  • 1-5 years: 92-248 ng/dL
  • 6-10 years: 93-231 ng/dL
  • 11-19 years: 91-218 ng/dL



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