Thyroid function tests#Free thyroxine index

Thyroid-stimulating hormone (TSH, thyrotropin) is generally increased in hypothyroidism and decreased in hyperthyroidism,[http://www.brooksidepress.org/Products/Military_OBGYN/Lab/ThyroidFunctionTests.htm Military Obstetrics & Gynecology > Thyroid Function Tests] In turn citing: Operational Medicine 2001, Health Care in Military Settings, NAVMED P-5139, May 1, 2001, Bureau of Medicine and Surgery, Department of the Navy, 2300 E Street NW, Washington, D.C., 20372-5300 {{cite web |url=http://pathcuric1.swmed.edu/PathDemo/nrrt.htm |title=Normal Reference Range Table |access-date=2011-12-25 |archive-url=https://web.archive.org/web/20111225185659/http://pathcuric1.swmed.edu/PathDemo/nrrt.htm |archive-date=25 December 2011 }} making it the most important test for early detection of both of these conditions.{{cite journal | last = Spencer| first = Carole| title = Assay of Thyroid Hormones and Related Substances |journal=Endotext [Internet] | year = 2000| pmid = 25905337}}{{cite book| last1 = Toft| first1 = Anthony| last2 = Beckett| first2 = Geoffrey| title = Werner & Ingbar's The Thyroid: A Fundamental & Clinical Text| publisher = Lippincott Williams & Wilkins| edition = 9th| date = 2005| location = Philadelphia, PA| pages = 329–344| url = http://www.msdlatinamerica.com/ebooks/WernerandIngbarsTheThyroidAFundamentalClinicalText/sid466393.html| isbn = 978-0-7817-5047-9| access-date = 2018-04-07| archive-date = 2020-05-06| archive-url = https://web.archive.org/web/20200506005447/http://www.msdlatinamerica.com/ebooks/WernerandIngbarsTheThyroidAFundamentalClinicalText/sid466393.html| url-status = dead}} The result of this assay is suggestive of the presence and cause of thyroid disease, since a measurement of elevated TSH generally indicates hypothyroidism, while a measurement of low TSH generally indicates hyperthyroidism. However, when TSH is measured by itself, it can yield misleading results, so additional thyroid function tests must be compared with the result of this test for accurate diagnosis.{{cite journal|last1=Hoermann|first1=Rudolf|last2=Midgley|first2=John E. M.|last3=Larisch|first3=Rolf|last4=Dietrich|first4=Johannes W.|title=Recent Advances in Thyroid Hormone Regulation: Toward a New Paradigm for Optimal Diagnosis and Treatment|journal=Frontiers in Endocrinology|date=22 December 2017|volume=8|page=364|doi=10.3389/fendo.2017.00364|pmid=29375474|pmc=5763098|doi-access=free}}{{cite journal |last1=Midgley |first1=JEM |last2=Toft |first2=AD |last3=Larisch |first3=R |last4=Dietrich |first4=JW |last5=Hoermann |first5=R |title=Time for a reassessment of the treatment of hypothyroidism. |journal=BMC Endocrine Disorders |date=18 April 2019 |volume=19 |issue=1 |page=37 |doi=10.1186/s12902-019-0365-4 |pmid=30999905|pmc=6471951 |doi-access=free }}

TSH is produced in the pituitary gland. The production of TSH is controlled by thyrotropin-releasing hormone (TRH), which is produced in the hypothalamus. TSH levels may be suppressed by excess free T3 (fT3) or free T4 (fT4) in the blood.{{citation needed|date=July 2020}}

First-generation TSH assays were done by radioimmunoassay and were introduced in 1965. There were variations and improvements upon TSH radioimmunoassay, but their use declined as a new immunometric assay technique became available in the middle of the 1980s. The new techniques were more accurate, leading to the second, third, and even fourth generations of TSH assay, with each generation possessing ten times greater functional sensitivity than the last.{{cite journal

| last1 = Spencer | first1 = Carole

| last2 = Takeuchi | first2 = Michael

| last3 = Kazarosyan | first3 = Margarita

| title = Current status and performance goals for serum thyrotropin (TSH) assays

| journal = Clinical Chemistry

| volume = 42

| issue = 1

| pages = 141–145

| date = 1996

| pmid = 8565217

| url = http://www.clinchem.org/content/42/1/140.long

| access-date = 5 November 2013}} Third generation immunometric assay methods are typically automated. Fourth generation TSH immunometric assay has been developed for use in research.

Third generation TSH assay is the requirement for modern standards of care. TSH testing in the United States is typically carried out with automated platforms using advanced forms of immunometric assay. Nonetheless, there is no international standard for measurement of thyroid-stimulating hormone.

Accurate interpretation takes a variety of factors into account, such as the thyroid hormones i.e. thyroxine (T₄) and triiodothyronine (T₃), current medical status (such as pregnancy), certain medications like propylthiouracil, temporal effects including circadian rhythm{{cite journal|last1=Hoermann|first1=Rudolf|last2=Midgley|first2=John E. M.|last3=Larisch|first3=Rolf|last4=Dietrich|first4=Johannes W.|title=Homeostatic Control of the Thyroid–Pituitary Axis: Perspectives for Diagnosis and Treatment|journal=Frontiers in Endocrinology|volume=6|doi=10.3389/fendo.2015.00177|pmid=26635726|page=177|pmc=4653296|year=2015|doi-access=free}} and hysteresis,{{cite journal|last1=Leow|first1=Melvin Khee-Shing|title=A Review of the Phenomenon of Hysteresis in the Hypothalamus–Pituitary–Thyroid Axis|journal=Frontiers in Endocrinology|volume=7|page=64|doi=10.3389/fendo.2016.00064|pmid=27379016|pmc=4905968|year=2016|doi-access=free}} and other past medical history.{{cite journal

| last = Dayan

| first = Colin

| title = Interpretation of thyroid function tests

| journal = The Lancet

| volume = 357

| issue = 9256

| pages = 619–624

| date = 24 February 2001

| url = http://keck.usc.edu/en/Education/Academic_Department_and_Divisions/Department_of_Medicine/Education_and_Training/Internal_Medicine_Residency/Resources/Articles/~/media/Docs/Departments/Medicine/Chief%20Resident/Articles/Endocrinology/TFTs.pdf

| access-date = 5 November 2013

| doi = 10.1016/s0140-6736(00)04060-5

| pmid = 11558500

| s2cid = 3278073

| archive-date = 25 June 2013

| archive-url = https://web.archive.org/web/20130625181731/http://keck.usc.edu/en/Education/Academic_Department_and_Divisions/Department_of_Medicine/Education_and_Training/Internal_Medicine_Residency/Resources/Articles/~/media/Docs/Departments/Medicine/Chief%20Resident/Articles/Endocrinology/TFTs.pdf

| url-status = dead

}}

Total thyroxine is rarely measured, having been largely superseded by free thyroxine tests. Total thyroxine (Total T₄) is generally elevated in hyperthyroidism and decreased in hypothyroidism. It is usually slightly elevated in pregnancy secondary to increased levels of thyroid binding globulin (TBG).

Total T4 is measured to see the bound and unbound levels of T4. The total T4 is less useful in cases where there could be protein abnormalities. The total T4 is less accurate due to the large amount of T4 that is bound. The total T3 is measured in clinical practice since the T3 has decreased amount that is bound as compared to T4.{{cn|date=November 2021}}

Reference ranges depend on the method of analysis. Results should always be interpreted using the range from the laboratory that performed the test. Example values are:

Free thyroxine (fT₄ or free T4) is generally elevated in hyperthyroidism and decreased in hypothyroidism.

Reference ranges depend on the method of analysis. Results should always be interpreted using the range from the laboratory that performed the test. Example values are:

Total triiodothyronine (Total T₃) is rarely measured, having been largely superseded by free T3 tests. Total T3 is generally elevated in hyperthyroidism and decreased in hypothyroidism.

Reference ranges depend on the method of analysis. Results should always be interpreted using the range from the laboratory that performed the test. Example values are:

Free triiodothyronine (fT₃ or free T3) is generally elevated in hyperthyroidism and decreased in hypothyroidism.

Reference ranges depend on the method of analysis. Results should always be interpreted using the range from the laboratory that performed the test. Example values are:

{{Main|Thyroxine-binding globulin}}

An increased thyroxine-binding globulin results in an increased total thyroxine and total triiodothyronine without an actual increase in hormonal activity of thyroid hormones.

Reference ranges:

Reference ranges:

• Transthyretin (prealbumin)
• Albumin

Thyroid hormone uptake (T_uptake or T_{3 uptake}) is a measure of the unbound thyroxine binding globulins in the blood, that is, the TBG that is unsaturated with thyroid hormone. Unsaturated TBG increases with decreased levels of thyroid hormones. It is not directly related to triiodothyronine, despite the name T_{3 uptake}.

Reference ranges:

• Thyroid Hormone Binding Ratio (THBR)
• Thyroxine-binding index (TBI)

The Free Thyroxine Index (FTI or T7) is obtained by multiplying the total T₄ with T₃ uptake. FTI is considered to be a more reliable indicator of thyroid status in the presence of abnormalities in plasma protein binding. This test is rarely used now that reliable free thyroxine and free triiodothyronine assays are routinely available.

FTI is elevated in hyperthyroidism and decreased in hypothyroidism.

File:Reference ranges for TSH, FT4, JTI and SPINA-GT.svg

Derived structure parameters that describe constant properties of the overall feedback control system may add useful information for special purposes, e.g. in diagnosis of nonthyroidal illness syndrome or central hypothyroidism.{{cite journal | pmid = 18851740 | doi=10.1186/1472-6823-8-13 | volume=8 | title=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 | pmc=2576461 | year=2008 |vauthors=Dietrich JW, Stachon A, Antic B, Klein HH, Hering S | journal=BMC Endocr Disord | page=13 | doi-access=free }}{{cite journal | pmid = 16230785 | volume=27 | issue=3 | title=Influence of low protein diet on nonthyroidal illness syndrome in chronic renal failure |date=August 2005 |vauthors=Rosolowska-Huszcz D, Kozlowska L, Rydzewski A | s2cid=25630198 | journal=Endocrine | pages=283–8 | doi=10.1385/ENDO:27:3:283}}{{cite journal | pmid = 22874844 | title=Nonthyroidal Illness Syndrome: Is it Far Away From Crohn's Disease? | year=2012|vauthors=Liu S, Ren J, Zhao Y, Han G, Hong Z, Yan D, Chen J, Gu G, Wang G, Wang X, Fan C, Li J | s2cid=35344744 | journal=J Clin Gastroenterol | doi = 10.1097/MCG.0b013e318254ea8a | pages = 153–9 | volume=47 | issue=2}}{{cite journal|last1=Dietrich|first1=Johannes W.|last2=Landgrafe-Mende|first2=Gabi|last3=Wiora|first3=Evelin|last4=Chatzitomaris|first4=Apostolos|last5=Klein|first5=Harald H.|last6=Midgley|first6=John E. M.|last7=Hoermann|first7=Rudolf|title=Calculated Parameters of Thyroid Homeostasis: Emerging Tools for Differential Diagnosis and Clinical Research|journal=Frontiers in Endocrinology|date=9 June 2016|volume=7|doi=10.3389/fendo.2016.00057|pmid=27375554|pmc=4899439|page=57|doi-access=free}}

{{Main|Thyroid's secretory capacity}}

Thyroid's secretory capacity (G_T, also referred to as SPINA-GT) is the maximum stimulated amount of thyroxine the thyroid can produce in one second.{{Cite book

|publisher = Logos-Verlag Berlin

|isbn = 978-3-89722-850-4

|location = Berlin, Germany

|title = Der Hypophysen-Schilddrüsen-Regelkreis

|author = Dietrich, J. W.

|date = 2002

|oclc = 50451543

|id = 3897228505

|ol = 24586469M

}} G_T is elevated in hyperthyroidism and reduced in hypothyroidism.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.

G_T is calculated with

$\backslash hat\; G\_T\; =\; \{\{\backslash beta\; \_T\; (D\_T\; +\; [TSH])(1\; +\; K\_\{41\}\; [TBG]\; +\; K\_\{42\}\; [TBPA])[FT\_4\; ]\}\; \backslash over\; \{\backslash alpha\; \_T\; [TSH]\}\}$

or

$\backslash hat\; G\_T\; =\; \{\{\backslash beta\; \_T\; (D\_T\; +\; [TSH])[TT\_4\; ]\}\; \backslash over\; \{\backslash alpha\; \_T\; [TSH]\}\}$

$\backslash alpha\; \_T$: Dilution factor for T4 (reciprocal of apparent volume of distribution, 0.1 l⁻¹)

$\backslash beta\; \_T$: Clearance exponent for T4 (1.1e-6 sec⁻¹)

K₄₁: Dissociation constant T4-TBG (2e10 L/mol)

K₄₂: Dissociation constant T4-TBPA (2e8 L/mol)

D_T: EC₅₀ for TSH (2.75 mU/L)

{{Main|Sum activity of peripheral deiodinases}}

The sum activity of peripheral deiodinases (G_D, also referred to as SPINA-GD) is reduced in nonthyroidal illness with hypodeiodination.{{cite journal|last1=Fan|first1=S|last2=Ni|first2=X|last3=Wang|first3=J|last4=Zhang|first4=Y|last5=Tao|first5=S|last6=Chen|first6=M|last7=Li|first7=Y|last8=Li|first8=J|title=Low Triiodothyronine Syndrome in Patients With Radiation Enteritis: Risk Factors and Clinical Outcomes an Observational Study.|journal=Medicine|date=February 2016|volume=95|issue=6|pages=e2640|doi=10.1097/MD.0000000000002640|pmid=26871787|pmc=4753882}}

G_D is obtained with

$\backslash hat\; G\_D\; =\; \{\{\backslash beta\; \_\{31\}\; (K\_\{M1\}\; +\; [FT\_4\; ])(1\; +\; K\_\{30\}\; [TBG])[FT\_3\; ]\}\; \backslash over\; \{\backslash alpha\; \_\{31\}\; [FT\_4\; ]\}\}$

or

$\backslash hat\; G\_D\; =\; \{\{\backslash beta\; \_\{31\}\; (K\_\{M1\}\; +\; [FT\_4\; ])[TT\_3\; ]\}\; \backslash over\; \{\backslash alpha\; \_\{31\}\; [FT\_4\; ]\}\}$

$\backslash alpha\; \_\{31\}$: Dilution factor for T3 (reciprocal of apparent volume of distribution, 0.026 L⁻¹)

$\backslash beta\; \_\{31\}$: Clearance exponent for T3 (8e-6 sec⁻¹)

K_M1: Dissociation constant of type-1-deiodinase (5e-7 mol/L)

K₃₀: Dissociation constant T3-TBG (2e9 L/mol)

{{Main|Jostel's TSH index}}

Jostel's TSH index (JTI or TSHI) helps to determine thyrotropic function of anterior pituitary on a quantitative level.{{cite journal | pmid = 19226261 | doi=10.1111/j.1365-2265.2009.03534.x | volume=71 | issue=4 | title=The use of thyroid function tests in the diagnosis of hypopituitarism: definition and evaluation of the TSH Index |date=October 2009 |vauthors=Jostel A, Ryder WD, Shalet SM | journal=Clin. Endocrinol. | pages=529–34| s2cid=10827131 }} It is reduced in thyrotropic insufficiency and in certain cases of non-thyroidal illness syndrome.

It is calculated with

$TSHI\; =\; LN(TSH)\; +\; 0.1345\; *\; FT4$.

Additionally, a standardized form of TSH index may be calculated with

$sTSHI\; =\; (TSHI\; -\; 2.7)/0.676$.

{{Main|Thyrotroph Thyroid Hormone Sensitivity Index}}

The Thyrotroph Thyroid Hormone Sensitivity Index (TTSI, also referred to as Thyrotroph T4 Resistance Index or TT4RI) was developed to enable fast screening for resistance to thyroid hormone.{{cite journal | pmid = 9141558 | doi=10.1210/jcem.82.5.3945 | volume=82 | issue=5 | title=Resistance to thyroid hormone caused by two mutant thyroid hormone receptors beta, R243Q and R243W, with marked impairment of function that cannot be explained by altered in vitro 3,5,3'-triiodothyroinine binding affinity | year=1997 | journal=J. Clin. Endocrinol. Metab. | pages=1608–14 | vauthors=Yagi H, Pohlenz J, Hayashi Y, Sakurai A, Refetoff S| doi-access=free }}{{cite journal | pmid = 10566629 | doi=10.1210/jcem.84.11.6080 | volume=84 | issue=11 | title=Five new families with resistance to thyroid hormone not caused by mutations in the thyroid hormone receptor beta gene | year=1999 | journal=J. Clin. Endocrinol. Metab. | pages=3919–28 | vauthors=Pohlenz J, Weiss RE, Macchia PE, Pannain S, Lau IT, Ho H, Refetoff S| doi-access=free }} Somewhat similar to the TSH Index it is calculated from equilibrium values for TSH and FT4, however with a different equation.

{{Main|Thyroid Feedback Quantile-based Index}}

The Thyroid Feedback Quantile-based Index (TFQI) is another parameter for thyrotropic pituitary function. It was defined to be more robust to distorted data than JTI and TTSI. It is calculated with

$TFQI\; =\; F\_\{FT4\}(FT4)\; -\; (1\; -\; F\_\{TSH\}(TSH))$

from quantiles of FT4 and TSH concentration (as determined based on cumulative distribution functions).{{cite journal |last1=Laclaustra |first1=M |last2=Moreno-Franco |first2=B |last3=Lou-Bonafonte |first3=JM |last4=Mateo-Gallego |first4=R |last5=Casasnovas |first5=JA |last6=Guallar-Castillon |first6=P |last7=Cenarro |first7=A |last8=Civeira |first8=F |title=Impaired Sensitivity to Thyroid Hormones Is Associated With Diabetes and Metabolic Syndrome. |journal=Diabetes Care |date=February 2019 |volume=42 |issue=2 |pages=303–310 |doi=10.2337/dc18-1410 |pmid=30552134|doi-access=free }} Per definition the TFQI has a mean of 0 and a standard deviation of 0.37 in a reference population. Higher values of TFQI are associated with obesity, metabolic syndrome, impaired renal function, diabetes, and diabetes-related mortality.{{cite journal |title=Schilddrüsenhormonresistenz und Risiko für Diabetes und metabolisches Syndrom |journal=Diabetologie und Stoffwechsel |date=16 April 2019 |volume=14 |issue=2 |page=78 |doi=10.1055/a-0758-5718|s2cid=243074371 }}{{cite journal |last1=Paschou |first1=Stavroula A. |last2=Alexandrides |first2=Theodoros |s2cid=204786351 |title=A year in type 2 diabetes mellitus: 2018 review based on the Endorama lecture |journal=Hormones |date=19 October 2019 |volume=18 |issue=4 |pages=401–408 |doi=10.1007/s42000-019-00139-z|pmid=31630372 }}{{cite journal |last1=Guan |first1=Haixia |title=Mild Acquired Thyroid Hormone Resistance Is Associated with Diabetes-Related Morbidity and Mortality in the General Population |journal=Clinical Thyroidology |date=April 2019 |volume=31 |issue=4 |pages=138–140 |doi=10.1089/ct.2019;31.138-140|s2cid=145947179 }}{{cite journal |last1=Lou-Bonafonte |first1=José Manuel |last2=Civeira |first2=Fernando |last3=Laclaustra |first3=Martín |s2cid=211217245 |title=Quantifying Thyroid Hormone Resistance in Obesity |journal=Obesity Surgery |date=20 February 2020 |volume=30 |issue=6 |pages=2411–2412 |doi=10.1007/s11695-020-04491-7|pmid=32078724 }}{{cite web |title=甲状腺素抵抗与糖尿病和代谢综合征有关？看TFQI怎么说 |url=https://www.medinfo-sanofi.cn/zh-cn/feitangxindong/news/20190204-qklw-thyroxine-resistance |website=www.medinfo-sanofi.cn |access-date=14 April 2020 }}{{Dead link|date=January 2024 |bot=InternetArchiveBot |fix-attempted=yes }}{{cite journal |last1=Yang |first1=S |last2=Lai |first2=S |last3=Wang |first3=Z |last4=Liu |first4=A |last5=Wang |first5=W |last6=Guan |first6=H |title=Thyroid Feedback Quantile-based Index correlates strongly to renal function in euthyroid individuals. |journal=Annals of Medicine |date=December 2021 |volume=53 |issue=1 |pages=1945–1955 |doi=10.1080/07853890.2021.1993324 |pmid=34726096|pmc=8567884 }} TFQI results are also elevated in takotsubo syndrome,{{cite journal |last1=Aweimer |first1=A |last2=El-Battrawy |first2=I |last3=Akin |first3=I |last4=Borggrefe |first4=M |last5=Mügge |first5=A |last6=Patsalis |first6=PC |last7=Urban |first7=A |last8=Kummer |first8=M |last9=Vasileva |first9=S |last10=Stachon |first10=A |last11=Hering |first11=S |last12=Dietrich |first12=JW |title=Abnormal thyroid function is common in takotsubo syndrome and depends on two distinct mechanisms: results of a multicentre observational study. |journal=Journal of Internal Medicine |date=12 November 2020 |volume=289 |issue=5 |pages=675–687 |doi=10.1111/joim.13189 |pmid=33179374|doi-access=free }} potentially reflecting type 2 allostatic load in the situation of psychosocial stress. Reductions have been observed in subjects with schizophrenia after initiation of therapy with oxcarbazepine, potentially reflecting declining allostatic load.{{cite journal |last1=Zhai |first1=D |last2=Chen |first2=J |last3=Guo |first3=B |last4=Retnakaran |first4=R |last5=Gao |first5=S |last6=Zhang |first6=X |last7=Hao |first7=W |last8=Zhang |first8=R |last9=Zhao |first9=Y |last10=Wen |first10=SW |title=Oxcarbazepine was associated with risks of newly developed hypothyroxinemia and impaired central set point of thyroid homeostasis in schizophrenia patients. |journal=British Journal of Clinical Pharmacology |date=1 December 2021 |volume=88 |issue=5 |pages=2297–2305 |doi=10.1111/bcp.15163 |pmid=34855997|s2cid=244818801 |doi-access=free }}

In healthy persons, the intra-individual variation of TSH and thyroid hormones is considerably smaller than the inter-individual variation.{{cite journal |last1=Andersen |first1=S |last2=Pedersen |first2=KM |last3=Bruun |first3=NH |last4=Laurberg |first4=P |title=Narrow individual variations in serum T(4) and T(3) in normal subjects: a clue to the understanding of subclinical thyroid disease. |journal=The Journal of Clinical Endocrinology and Metabolism |date=March 2002 |volume=87 |issue=3 |pages=1068–72 |doi=10.1210/jcem.87.3.8165 |pmid=11889165|doi-access=free }}{{cite journal |last1=Larisch |first1=R |last2=Giacobino |first2=A |last3=Eckl |first3=W |last4=Wahl |first4=HG |last5=Midgley |first5=JE |last6=Hoermann |first6=R |title=Reference range for thyrotropin. Post hoc assessment. |journal=Nuklearmedizin. Nuclear Medicine |date=2015 |volume=54 |issue=3 |pages=112–7 |doi=10.3413/Nukmed-0671-14-06 |pmid=25567792|s2cid=9607904 }}{{cite journal |last1=Hoermann |first1=R |last2=Midgley |first2=JEM |last3=Larisch |first3=R |last4=Dietrich |first4=JW |title=Functional and Symptomatic Individuality in the Response to Levothyroxine Treatment. |journal=Frontiers in Endocrinology |date=2019 |volume=10 |page=664 |doi=10.3389/fendo.2019.00664 |pmid=31616383|pmc=6775211 |doi-access=free }} This results from a personal set point of thyroid homeostasis.{{cite journal |last1=Cappola |first1=AR |last2=Desai |first2=AS |last3=Medici |first3=M |last4=Cooper |first4=LS |last5=Egan |first5=D |last6=Sopko |first6=G |last7=Fishman |first7=GI |last8=Goldman |first8=S |last9=Cooper |first9=DS |last10=Mora |first10=S |last11=Kudenchuk |first11=PJ |last12=Hollenberg |first12=AN |last13=McDonald |first13=CL |last14=Ladenson |first14=PW |title=Thyroid and Cardiovascular Disease Research Agenda for Enhancing Knowledge, Prevention, and Treatment. |journal=Circulation |date=13 May 2019 |volume=139 |issue=25 |pages=2892–2909 |doi=10.1161/CIRCULATIONAHA.118.036859 |pmid=31081673|pmc=6851449 |hdl=10150/633369 |hdl-access=free }} In hypothyroidism, it is impossible to directly access the set point,{{cite journal |last1=Hoermann |first1=R |last2=Midgley |first2=JEM |last3=Larisch |first3=R |last4=Dietrich |first4=JW |title=Individualised requirements for optimum treatment of hypothyroidism: complex needs, limited options. |journal=Drugs in Context |date=2019 |volume=8 |page=212597 |doi=10.7573/dic.212597 |pmid=31516533|pmc=6726361 |doi-access=free }} but it can be reconstructed with methods of systems theory.{{cite journal |last1=Goede |first1=SL |last2=Leow |first2=MK |last3=Smit |first3=JW |last4=Dietrich |first4=JW |title=A novel minimal mathematical model of the hypothalamus-pituitary-thyroid axis validated for individualized clinical applications. |journal=Mathematical Biosciences |date=March 2014 |volume=249 |pages=1–7 |doi=10.1016/j.mbs.2014.01.001 |pmid=24480737}}{{cite journal |last1=Goede |first1=SL |last2=Leow |first2=MK |last3=Smit |first3=JW |last4=Klein |first4=HH |last5=Dietrich |first5=JW |title=Hypothalamus-pituitary-thyroid feedback control: implications of mathematical modeling and consequences for thyrotropin (TSH) and free thyroxine (FT4) reference ranges. |journal=Bulletin of Mathematical Biology |date=June 2014 |volume=76 |issue=6 |pages=1270–87 |doi=10.1007/s11538-014-9955-5 |pmid=24789568|s2cid=23894743 }}{{cite journal |last1=Leow |first1=MK |last2=Goede |first2=SL |title=The homeostatic set point of the hypothalamus-pituitary-thyroid axis--maximum curvature theory for personalized euthyroid targets. |journal=Theoretical Biology & Medical Modelling |date=8 August 2014 |volume=11 |page=35 |doi=10.1186/1742-4682-11-35 |pmid=25102854|pmc=4237899 |doi-access=free }}

A computerised algorithm, called Thyroid-SPOT, which is based on this mathematical theory, has been implemented in software applications.{{cite journal |last1=Sim |first1=Jia-Zhi |last2=Zang |first2=Yu |last3=Nguyen |first3=Phi-Vu |last4=Leow |first4=Melvin Khee-Shing |last5=Gan |first5=Samuel Ken-En |title=Thyroid-SPOT for mobile devices: personalised thyroid treatment management app |journal=Scientific Phone Apps and Mobile Devices |date=December 2017 |volume=3 |issue=1 |page=4 |doi=10.1186/s41070-017-0016-y|doi-access=free }} In patients undergoing thyroidectomy it could be demonstrated that this algorithm can be used to reconstruct the personal set point with sufficient precision.{{cite journal |last1=Li |first1=E |last2=Yen |first2=PM |last3=Dietrich |first3=JW |last4=Leow |first4=MK |title=Profiling retrospective thyroid function data in complete thyroidectomy patients to investigate the HPT axis set point (PREDICT-IT). |journal=Journal of Endocrinological Investigation |date=17 August 2020 |volume=44 |issue=5 |pages=969–977 |doi=10.1007/s40618-020-01390-7 |pmid=32808162|s2cid=221146170 }}

Drugs can profoundly affect thyroid function tests. Listed below is a selection of important effects.

↓: reduced serum concentration or structure parameter; ↑: increased serum concentration or structure parameter; ↔: no change; TSH: Thyroid-stimulating hormone; T₃: Total triiodothyronine; T₄: Total thyroxine; fT₄: Free thyroxine; fT₃: Free triiodothyronine; rT₃: Reverse triiodothyronine

• Reference ranges for thyroid hormones

Image:Blood values sorted by mass and molar concentration.png, sorted by mass and molar concentration, with thyroid function tests marked in purple boxes in left half of diagram.]]

• Long-acting thyroid stimulator (LATS)

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• American Thyroid Association: [http://www.thyroid.org/blood-test-for-thyroid/ Thyroid Function Tests]. Posted on June 4, 2012, seen on January 9, 2013.
• [http://labtestsonline.org/understanding/analytes/thyroid-panel/tab/test Thyroid function panel - Lab Tests Online]

• [http://spina.sf.net SPINA Thyr: Open source software for calculating GT and GD]
• [https://web.archive.org/web/20170212093006/https://pdfs.semanticscholar.org/5fe5/97829d6859a84190cf47e71310426588b72c.pdf Interpretation of thyroid function tests] by Dayan, Colin M. 2001. The Lancet, Vol. 357.

The Centers for Disease Control and Prevention has published the following laboratory procedure manuals for measuring thyroid-stimulating hormone:

• [https://www.cdc.gov/NCHS/data/nhanes/nhanes_09_10/THYROD_F_met_TSH.pdf Thyroid Stimulating Hormone (TSH) (University of Washington Medical Center)]. September 2011. Method: Access 2 (Beckman Coulter).
• [https://www.cdc.gov/NCHS/data/nhanes/nhanes_09_10/THYROD_F_met_TSH_CLS.pdf Thyroid Stimulating Hormone (TSH) (Collaborative Laboratory Services)]. September 2011. Method: Access 2 (Beckman Coulter).
• [https://www.cdc.gov/nchs/data/nhanes/nhanes_07_08/THYROD_e_met_Thyroid_Stimulating_Hormone.pdf Thyroid Stimulating Hormone (TSH)]. September 2009. Method: Access 2 (Beckman Coulter).
• [https://www.cdc.gov/nchs/data/nhanes/nhanes_01_02/l18t4_b_met_b_tsh.pdf Lab 18 Thyroid Stimulating Hormone]. 2001-2002. Method: Microparticle Enzyme Immunoassay.
• [https://www.cdc.gov/nchs/data/nhanes/nhanes_99_00/lab18_met_tsh.pdf Lab 18 TSH - Thyroid Stimulating Hormone]. 1999-2000. Method: Microparticle Enzyme Immunoassay.

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Category:Chemical pathology

Category:Blood tests

Category:Endocrine procedures

Category:Thyroidological methods

Category:Endocrine function tests