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{{Interventions infobox |
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  Name        = Thyroid function tests |
  Image      = |
  Caption    = |
  ICD10      = |
  ICD9        = |
  MeshID      = D013960 |
  MedlinePlus = 003444 |
  OtherCodes  = |
}}
'''Thyroid function tests''' ('''TFTs''') is a collective term for [[blood test]]s used to check the function of the [[thyroid]].<ref name="pmid11558500">{{cite journal |author=Dayan CM |title=Interpretation of thyroid function tests |journal=Lancet |volume=357 |issue=9256 |pages=619–24 |date=February 2001 |pmid=11558500 |doi=10.1016/S0140-6736(00)04060-5 |url=http://linkinghub.elsevier.com/retrieve/pii/S0140-6736(00)04060-5}}</ref>
 
TFTs may be requested if a patient is thought to suffer from [[hyperthyroidism]] (overactive thyroid) or [[hypothyroidism]] (underactive thyroid), or to monitor the effectiveness of either thyroid-suppression or hormone replacement therapy. It is also requested routinely in conditions linked to thyroid disease, such as [[atrial fibrillation]] and [[anxiety disorder]].
 
A TFT [[test panel|panel]] typically includes [[thyroid hormones]] such as [[thyroid-stimulating hormone]] (TSH, thyrotropin) and [[thyroxine]] (T4), and [[triiodothyronine]] (T3) depending on local laboratory policy.
 
==Thyroid hormones==
 
===Thyroid-stimulating hormone===
{{Main|Thyroid-stimulating hormone measurement}}
[[Thyroid-stimulating hormone]] (TSH, thyrotropin) is generally elevated in hypothyroidism and decreased in hyperthyroidism.<ref name=brooksidepress>[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</ref>
 
It is the most sensitive test for thyroid hormone function.  TSH is produced in the pituitary gland. The production of TSH is controlled by TRH, which is produced in the hypothalamus.  TSH levels may be suppressed by excess free T3 or free T4 in the blood.
 
===Total thyroxine===
Total thyroxine is rarely measured, having been largely superseded by free thyroxine tests. Total [[thyroxine]] (Total T<sub>4</sub>) is generally elevated in [[hyperthyroidism]] and decreased in [[hypothyroidism]].<ref name=brooksidepress/> It is usually slightly elevated in pregnancy secondary to increased levels of [[thyroid binding globulin]] (TBG).<ref name=brooksidepress/>
 
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 measure in clinical practice since the T3 has decreased amount that is bound as compared to T4.
 
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:
{| class="wikitable"
|'''Lower limit'''||'''Upper limit'''||'''Unit'''
|-
| 4,<ref name=manager/> 5.5<ref name=southwest>[http://pathcuric1.swmed.edu/PathDemo/nrrt.htm Normal Reference Range Table] from The University of Texas Southwestern Medical Center at Dallas. Used in Interactive Case Study Companion to Pathologic basis of disease.</ref> || 11,<ref name=manager/> 12.3<ref name=southwest/> || μg/dL
|-  
| 60<ref name=manager/><ref name=Watt/>  || 140,<ref name=manager/> 160<ref name=Watt/> || nmol/L 
|-
|}
 
===Free thyroxine===
Free [[thyroxine]] (Free T<sub>4</sub>) is generally elevated in [[hyperthyroidism]] and decreased in [[hypothyroidism]].<ref name=brooksidepress/>
 
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:
 
{| class="wikitable"
|'''Patient type'''||'''Lower limit'''||'''Upper limit'''||'''Unit'''
  |-
|rowspan=2| Normal adult || 0.7,<ref name=unc>[http://labs.unchealthcare.org/labstestinfo/f_tests/free_t4.htm Free T4; Thyroxine, Free; T4, Free] UNC Health Care System</ref> 0.8<ref name=southwest/> || 1.4,<ref name=unc/> 1.5,<ref name=southwest/> 1.8<ref name=thyroxine-molar>Derived from molar values using molar mass of 776.87 g/mol</ref> || ng/dL
|-
| 9,<ref name=uppsala>Reference range list from Uppsala University Hospital ("Laborationslista"). Artnr 40284 Sj74a. Issued on April 22, 2008</ref><ref name=th-mass/> 10,<ref name=manager/> 12 <ref name=Watt>{{cite journal |author=van der Watt G, Haarburger D, Berman P |title=Euthyroid patient with elevated serum free thyroxine |journal=Clin. Chem. |volume=54 |issue=7 |pages=1239–41 |date=July 2008 |pmid=18593963 |doi=10.1373/clinchem.2007.101428 |url=http://www.clinchem.org/cgi/content/full/54/7/1239}}</ref> || 18,<ref name=uppsala/><ref name=th-mass>Derived from mass values using molar mass of 776.87 g/mol</ref> 23<ref name=Watt/> || pmol/L
|-
|rowspan=2| Infant 0–3 d || 2.0<ref name=unc/> || 5.0<ref name=unc/> || ng/dL
|-
| 26<ref name=th-mass/> || 65<ref name=th-mass/> || pmol/L
|-
|rowspan=2| Infant 3–30 d || 0.9<ref name=unc/> || 2.2<ref name=unc/> || ng/dL
|-
| 12<ref name=th-mass/> || 30<ref name=th-mass/> || pmol/L
|-
|rowspan=2| Child/Adolescent <br> 31 d – 18 y || 0.8<ref name=unc/> || 2.0<ref name=unc/> || ng/dL
|-
| 10<ref name=th-mass/> || 26<ref name=th-mass/> || pmol/L
|-
|rowspan=2| Pregnant || 0.5<ref name=unc/> || 1.0<ref name=unc/> || ng/dL
|-
| 6.5<ref name=th-mass/> || 13<ref name=th-mass/> || pmol/L
|-
|}
 
===Total triiodothyronine===
Total [[triiodothyronine]] (Total T<sub>3</sub>) is rarely measured, having been largely superseded by free T3 tests. Total T3 is generally elevated in hyperthyroidism and decreased in hypothyroidism.<ref name=brooksidepress/>
 
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:
{| class="wikitable"
|'''Test'''||'''Lower limit'''||'''Upper limit'''||'''Unit'''
|-
|rowspan=2| Total [[triiodothyronine]] || 60,<ref name=southwest/> 75<ref name=manager>[http://www.thyroidmanager.org/chapter6/Ch-6b-2.htm Table 4: Typical reference ranges for serum assays] - Thyroid Disease Manager</ref> || 175,<ref name=manager/> 181<ref name=southwest/> || ng/dL
|-
| 0.9,<ref name=uppsala/> 1.1<ref name=manager/> || 2.5,<ref name=uppsala/> 2.7<ref name=manager/> ||  nmol/L
|-
|}
 
===Free triiodothyronine===
Free [[triiodothyronine]] (Free T<sub>3</sub>) is generally elevated in hyperthyroidism and decreased in hypothyroidism.<ref name=brooksidepress/>
 
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:
{| class="wikitable"
|'''Patient type'''||'''Lower limit'''||'''Upper limit'''||'''Unit'''
|-
|rowspan=2| Normal adult || 3.0<ref name=manager/> || 7.0<ref name=manager/> || pg/mL
|-
| 3.1<ref name=triiodo-mass>Derived from mass values using molar mass of 650.98 g/mol</ref> || 7.7<ref name=triiodo-mass/> || pmol/L
|-
|rowspan=2| Children 2–16 y || 3.0<ref name=CIOFFI>{{cite journal |author=Cioffi M, Gazzerro P, Vietri MT, ''et al.'' |title=Serum concentration of free T3, free T4 and TSH in healthy children |journal=J. Pediatr. Endocrinol. Metab. |volume=14 |issue=9 |pages=1635–9 |year=2001 |pmid=11795654 |doi=10.1515/JPEM.2001.14.9.1635 }}</ref> || 7.0<ref name=CIOFFI/> || pg/mL
|-
| 1.5<ref name=triiodo-mass/> || 9.2<ref name=triiodo-mass/> || pmol/L
|-
|}
 
==Carrier proteins==
 
===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:
{| class="wikitable"
|'''Lower limit'''||'''Upper limit'''||'''Unit'''
|-
| 12<ref name=southwest/> || 30<ref name=southwest/> || mg/L
|-
|}
 
===Thyroglobulin===
Reference ranges:
{| class="wikitable"
|'''Lower limit'''||'''Upper limit'''||'''Unit'''
|-
| 1.5<ref name=manager/>|| 30<ref name=manager/> || pmol/L
|-
| 1<ref name=manager/> || 20 <ref name=manager/> || μg/L 
|-
|}
 
===Other binding hormones===
*[[Transthyretin]] (prealbumin)
*[[Albumin]]
 
==Protein binding function==
 
===Thyroid hormone uptake===
Thyroid hormone uptake (T<sub>uptake</sub> or T<sub>3 uptake</sub>) is a measure of the unbound [[thyroxine binding globulin]]s in the blood, that is, the TBG that is unsaturated with thyroid hormone.<ref name=brooksidepress/> Unsaturated TBG increases with decreased levels of thyroid hormones. It is not directly related to triiodothyronine, despite the name T<sub>3 uptake</sub>.<ref name=brooksidepress/>
 
Reference ranges:
{| class="wikitable"
|'''Patient type'''||'''Lower limit'''||'''Upper limit'''||'''Unit'''
|-
| Females || 25<ref name=brooksidepress/> || 35<ref name=brooksidepress/> || %
|-
| In pregnancy || 15<ref name=brooksidepress/> || 25<ref name=brooksidepress/> || %
|-
| Males || 25<ref name=brooksidepress/> || 35<ref name=brooksidepress/> || %
|-
|}
 
===Other protein binding tests===
* [[Thyroid hormone binding ratio]] (THBR)
* [[Thyroxine-binding index]] (TBI)
 
==Mixed parameters==
 
===Free thyroxine index===
The Free Thyroxine Index (FTI or T7) is obtained by multiplying the total T<sub>4</sub> with T<sub>uptake</sub>.<ref name=brooksidepress/> FTI is considered to be a more reliable indicator of thyroid status in the presence of abnormalities in plasma protein binding.<ref name=brooksidepress/> 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.<ref name=brooksidepress/>
 
{| class="wikitable"
|'''Patient type'''||'''Lower limit'''||'''Upper limit'''||'''Unit'''
|-
| Females || 1.8<ref name=brooksidepress/> || 5.0<ref name=brooksidepress/> ||
|-
| Males || 1.3<ref name=brooksidepress/> || 4.2<ref name=brooksidepress/> ||
|-
|}
 
==Structure parameters==
For special purposes, e.g. in diagnosis of [[Euthyroid sick syndrome|nonthyroidal illness syndrome]] or [[secondary hypothyroidism|central hypothyroidism]], derived [[structure parameter]]s that describe constant properties of the overall [[Thyroid homeostasis|feedback control system]], may add useful information.<ref name=dietrich2008>Dietrich, J. W., A. Stachon, B. Antic, H. H. Klein, and S. Hering (2008). "[http://www.biomedcentral.com/1472-6823/8/13 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). [http://www.ncbi.nlm.nih.gov/pubmed/18851740?dopt=Abstract PMID 18851740].</ref><ref name=Rosolowska-Huszcz2005>{{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 | author=Rosolowska-Huszcz D, Kozlowska L, Rydzewski A | journal=Endocrine | pages=283–8 | doi=10.1385/ENDO:27:3:283}}</ref><ref name=Liu2012>{{cite journal | pmid = 22874844 | title=Nonthyroidal Illness Syndrome: Is it Far Away From Crohn's Disease? | year=2012| author=Liu S, Ren J, Zhao Y, Han G, Hong Z, Yan D, Chen J, Gu G, Wang G, Wang X, Fan C, Li J | journal=J Clin Gastroenterol. | doi = 10.1097/MCG.0b013e318254ea8a | pages = 1}}</ref>
 
===Secretory capacity (GT)===
[[Thyroid's secretory capacity]] (GT, also referred to as SPINA-GT) is the maximum stimulated amount of thyroxine the thyroid can produce in one second.<ref name=dietrich2002>{{Cite book
|publisher = Logos-Verlag Berlin
|isbn = 978-3-89722-850-4
|publication-place = Berlin, Germany
|title = Der Hypophysen-Schilddrüsen-Regelkreis
|url = http://openlibrary.org/books/OL24586469M/Der_Hypophysen-Schilddrüsen-Regelkreis
|author = Dietrich, J. W.
|publication-date = 2002
|oclc = 50451543
|id = 3897228505
|postscript = <!-- Bot inserted parameter. Either remove it; or change its value to "." for the cite to end in a ".", as necessary. -->{{inconsistent citations}}
}}</ref> GT is elevated in hyperthyroidism and reduced in hypothyroidism.<ref name=dietrich1999>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.</ref>
 
GT is calculated with
 
<math>\hat G_T  = {{\beta _T (D_T  + [TSH])(1 + K_{41} [TBG] + K_{42} [TBPA])[FT_4 ]} \over {\alpha _T [TSH]}}</math>
 
or
 
<math>\hat G_T = {{\beta _T (D_T  + [TSH])[TT_4 ]} \over {\alpha _T [TSH]}}</math>
 
<math>\alpha _T</math>: Dilution factor for T4 (reciprocal of apparent volume of distribution, 0.1 l<sup>−1</sup>)<br />
<math>\beta _T</math>: Clearance exponent for T4 (1.1e-6 sec<sup>−1</sup>)<br />
''K''<sub>41</sub>: Dissociation constant T4-TBG (2e10 l/mol)<br />
''K''<sub>42</sub>: Dissociation constant T4-TBPA (2e8 l/mol)<br />
''D''<sub>''T''</sub>: EC<sub>50</sub> for TSH (2.75 mU/l)<ref name=dietrich2002/>
 
{| class="wikitable"
|'''Lower limit'''||'''Upper limit'''||'''Unit'''
|-
| 1.41<ref name=dietrich2002/> || 8.67<ref name=dietrich2002/> ||  pmol/s
|-
|}
 
==== External links ====
[http://spina.sf.net SPINA Thyr: Open source software for calculating GT and GD]
 
===Sum activity of peripheral deiodinases (GD)===
The [[sum activity of peripheral deiodinases]] (GD, also referred to as SPINA-GD) is reduced in nonthyroidal illness with hypodeiodination.<ref name=Rosolowska-Huszcz2005/><ref name=Liu2012/>
 
GD is obtained with
 
<math>\hat G_D  = {{\beta _{31} (K_{M1}  + [FT_4 ])(1 + K_{30} [TBG])[FT_3 ]} \over {\alpha _{31} [FT_4 ]}}</math>
 
or
 
<math>\hat G_D  = {{\beta _{31} (K_{M1}  + [FT_4 ])[TT_3 ]} \over {\alpha _{31} [FT_4 ]}}</math>
 
<math>\alpha _{31}</math>: Dilution factor for T3 (reciprocal of apparent volume of distribution, 0.026 l<sup>−1</sup>)<br />
<math>\beta _{31}</math>: Clearance exponent for T3 (8e-6 sec<sup>−1</sup>)<br />
''K''<sub>''M''1</sub>: Dissociation constant of type-1-deiodinase (5e-7&nbsp;mol/l)<br />
''K''<sub>30</sub>: Dissociation constant T3-TBG (2e9 l/mol)<ref name=dietrich2002/>
 
{| class="wikitable"
|'''Lower limit'''||'''Upper limit'''||'''Unit'''
|-
| 20<ref name=dietrich2002/> || 40<ref name=dietrich2002/> ||  nmol/s
|-
|}
 
==== External links ====
* [http://spina.sf.net SPINA Thyr: Open source software for calculating GT and GD]
 
===TSH index===
Jostel's TSH index (TSHI) helps to determine thyrotropic function of anterior [[pituitary]] on a quantitative level.<ref name=jostel2009>{{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 | author=Jostel A, Ryder WD, Shalet SM | journal=Clin. Endocrinol. (Oxf) | pages=529–34}}</ref>
 
It is calculated with
 
<math>TSHI = LN(TSH) + 0.1345 * FT4</math>.
 
Additionally, a standardized form of TSH index may be calculated with
 
<math>sTSHI = (TSHI - 2.7)/0.676</math>.<ref name=jostel2009/>
 
{| class="wikitable"
|'''Parameter'''||'''Lower limit'''||'''Upper limit'''||'''Unit'''
|-
|TSHI || 1.3<ref name=jostel2009/> || 4.1<ref name=jostel2009/> || 
|-
|sTSHI || -2<ref name=jostel2009/> || 2<ref name=jostel2009/> || 
|-
|}
 
==See also==
* [[Reference ranges for blood tests#Hormones]]
[[Image:Blood values sorted by mass and molar concentration.png|thumb|center|700px|[[Reference ranges for blood tests]], sorted by mass and molar concentration, with thyroid function tests marked in <span style="color:purple;">purple boxes</span> in left half of diagram.]]
 
==References==
{{reflist|2}}
 
{{Blood tests}}
 
== Additional Resources ==
* 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]
[[Category:Chemical pathology]]
[[Category:Blood tests]]
[[Category:Endocrine procedures]]
[[Category:Thyroidological methods]]

Revision as of 18:01, 3 March 2014

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