Triiodothyronine (T3)

TRIIODOTHYRONINE, FREE (T3)

The thyroid produces and secretes triiodothyronine (10–20 %) and thyroxine (80–90 %). Together these hormones regulate body temperature, metabolism, and heart rate. Most of the triiodothyronine (T3) in the body is bound to carrier proteins. T3 that is not bound to protein is called free T3. Free T3 is immediately available for the physiological needs of the body. It is therefore measured to assess thyroid function on a cellular level or the level of thyroid medication.

• Reference range: 2.6–5.0 pmol/L

No optimal range has been established in terms of mortality, the prevention of cardiovascular diseases, etc. Recommendations often suggest levels that fall in the reference range's middle or top third (not in the bottom third). The free triiodothyronine value in the healthy population is on average 4.43 ± 0.647 pmol/L when the reference range is 3.5–6.5 pmol/L. Thus, this value cannot be directly applied to the above reference range. However, it does suggest that the values of an individual not using thyroid medication should be near the middle of the reference range or closer to the upper limit.