[1][2] Today it is also used to get an estimate for the set point of thyroid homeostasis,[3] especially to assess dynamic thyrotropic adaptation of the anterior pituitary gland, including non-thyroidal illnesses.
[citation needed] In case of resistance to thyroid hormone, the magnitude of TTSI depends on which nucleotide in the THRB gene is mutated, but also on the genotype of coactivators.
[10] A variant of the TTSI that is not corrected for the upper limit of the FT4 reference range was shown to be significantly increased in offspring from long-lived siblings compared to their partners.
[11] Conversely, an elevated set point of thyroid homeostasis, as quantified by the TT4RI, is associated to higher prevalence of metabolic syndrome[3] and several harmonized criteria by the International Diabetes Federation, including triglyceride and HDL concentration and blood pressure.
[15][16][17] Negative correlation of the TTSI with the urinary excretion of certain phthalates suggests that endocrine disruptors may affect the central set point of thyroid homeostasis.