Jostel's TSH index

Jostel's TSH index can be calculated with

${\displaystyle TSHI=\ln(TSH)+0.1345\cdot FT4}$

from equilibrium serum concentrations of thyrotropin (TSH), free T4 (FT4) and a correction coefficient derived from the logarithmic standard model (β = 0.1345).

An alternative standardised form (standardised TSH index or sTSHI) is calculated with.[1]

${\displaystyle sTSHI={\frac {TSHI-2.7}{0.676}}}$

as a z-transformed value incorporating mean (2.7) and standard deviation (0.676) of TSHI in a reference population[5]

The TSH index is reduced in patients with secondary hypothyroidism resulting from thyrotropic insufficiency.[1][8][9] For this indication, it has, however, up to now only been validated in adults.[10] JTI was also found reduced in cases of TACITUS syndrome (non-thyroidal illness syndrome) as an example of type 1 thyroid allostasis[11][12]. Conversely, an elevated thyroid function index may serve as a biomarker for type 2 allostasis and contextual stress.[13]

Recent research demonstrated the TSH index to inversely correlate to thyroid's secretory capacity and thyroid volume.[14] It is unclear if this finding reflects shortcomings of the index (i.e. low specificity in the setting of subclinical hypothyroidism) or plastic responses of the pituitary gland to beginning hypothyroidism.

• Thyroid function tests
• Thyrotroph Thyroid Hormone Sensitivity Index
• Thyroid's secretory capacity
• Sum activity of peripheral deiodinases

• SPINA Thyr: Open source software for TSHI
• Package "SPINA" for the statistical environment R