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Thyroid's secretory capacity

The thyroid's secretory capacity, abbreviated GT (for "gain of thyroid"), denotes the maximum amount of thyroxine that the thyroid gland can produce in a given time unit (usually one second)[1]

It is elevated in cases of hyperthyroidism and decreased in hypothyroidism.[2][3]

GT can be calculated by means of a structure parameter inference approach (SPINA) from equilibrium levels of TSH and FT4. Calculating GT may add additional information in special conditions, e.g. in non-thyroidal illness syndrome or secondary hypothyroidism.[4][5] The retest reliability of calculated GT is higher than that of TSH or peripheral thyroid hormones.[3]

1 Calculation

GT is calculated with

GT = BetaT (DT + [TSH]) (1 + K41 [TBG] + K42 [TBPA]) [FT4] / (AlphaT [TSH])

or

GT = BetaT (DT + [TSH])[TT4]) / (AlphaT [TSH])

from levels of TSH and FT4 or TT4, respectively, and, optionally, the binding proteins TBG or transthyretin (TBPA).

AlphaT: Dilution factor for T4 (reciprocal of apparent volume of distribution, 0.1 l-1)
BetaT: Clearance exponent for T4 (1.1e-6 sec-1)
DT: EC50 for TSH (2.75 mU/l)[1]
K41: Dissociation constant T4-TBG (2e10 l/mol)
K42: Dissociation constant T4-TBPA (2e8 l/mol)

2 Reference range

for adult humans:

Lower limit Upper limit Unit
1.41[1] 8.67[1] pmol/s

3 See also

4 Web Link

SPINA Thyr: Open source software for calculating GT and GD

5 References

  1. ISBN 9783897228504
  2. Dietrich, J., M. Fischer, J. Jauch, E. Pantke, R. Gärtner und C. R. Pickardt (1999). "SPINA-THYR: A Novel Systems Theoretic Approach to Determine the Secretion Capacity of the Thyroid Gland." European Journal of Internal Medicine 10, Suppl. 1 (5/1999): S34.
  3. 3.0 3.1 Dietrich JW, Landgrafe, G, Fotiadou, EH. TSH and Thyrotropic Agonists: Key Actors in Thyroid Homeostasis Journal of Thyroid Research, vol. 2012, Article ID 351864, 29 pages, 2012. doi:10.1155/2012/351864. PMID 23365787.
  4. Dietrich, J. W., A. Stachon, B. Antic, H. H. Klein, and S. Hering (2008). "The AQUA-FONTIS Study: Protocol of a multidisciplinary, cross-sectional and prospective longitudinal study for developing standardized diagnostics and classification of non-thyroidal illness syndrome." BMC Endocrine Disorders 8 (13). PMID 18851740.
  5. Rosolowska-Huszcz D, Kozlowska L, Rydzewski A (2005). Influence of low protein diet on nonthyroidal illness syndrome in chronic renal failure. Endocrine. 27(3):283-8. PMID 16230785

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