Thyrotroph T3 Sensitivity Index (TSHI-2)
Assessing pituitary feedback sensitivity to Free T3
Last updated on: July 6, 2025
TSHI-2 Calculator
What is the TSHI-2?
The Thyrotroph T3 Sensitivity Index (TSHI-2) is a calculated marker that evaluates the negative feedback relationship between Free T3 and TSH. It helps to quantify how sensitively the pituitary gland responds to circulating active thyroid hormone (T3).
While TSHI (based on FT4) reflects the feedback from the main thyroid hormone product, TSHI-2 reflects the feedback from the most biologically active hormone, providing a complementary view of the HPT axis regulation.
Why is it a Useful Complement?
- Offers a different perspective on central thyroid regulation focused on the active hormone, T3.
- May be useful in assessing conditions with altered T4 to T3 conversion.
- Helps in research settings to explore the nuances of the pituitary-thyroid feedback mechanism.
Interpreting the Result (Reference Guide)
Clinical Interpretation Notes
The TSHI-2 is an investigational index and does not have widely standardized reference ranges like TSH or FT4. Interpretation should be done with caution and in the context of the full clinical picture.
This page has been medically reviewed by Dr. Khoulah Attia – PharmD, Immunology Specialist.