Editing Hyperthyroidism (section)

==Diagnosis==
Measuring the level of [[thyroid-stimulating hormone]] (TSH), produced by the pituitary gland (which in turn is also regulated by the hypothalamus's TSH Releasing Hormone) in the blood is typically the initial test for suspected hyperthyroidism. A low TSH level typically indicates that the pituitary gland is being inhibited or "instructed" by the brain to cut back on stimulating the thyroid gland, having sensed increased levels of T<sub>4</sub> and/or T<sub>3</sub> in the blood. In rare circumstances, a low TSH indicates primary failure of the pituitary, or temporary inhibition of the pituitary due to another illness ([[euthyroid sick syndrome]]) and so checking the T<sub>4</sub> and T<sub>3</sub> is still clinically useful.<ref name="Thyrotoxicosis and Hyperthyroidism"/>

Measuring specific [[antibody|antibodies]], such as anti-TSH-receptor antibodies in Graves' disease, or anti-thyroid peroxidase in [[Hashimoto's thyroiditis]]—a common cause of [[hypothyroidism]]—may also contribute to the diagnosis. The diagnosis of hyperthyroidism is confirmed by blood tests that show a decreased thyroid-stimulating hormone (TSH) level and elevated T<sub>4</sub> and T<sub>3</sub> levels. TSH is a hormone made by the pituitary gland in the brain that tells the thyroid gland how much hormone to make. When there is too much thyroid hormone, the TSH will be low. A radioactive iodine uptake test and thyroid scan together characterizes or enables radiologists and doctors to determine the cause of hyperthyroidism. The uptake test uses radioactive iodine injected or taken orally on an empty stomach to measure the amount of iodine absorbed by the thyroid gland. Persons with hyperthyroidism absorb much more iodine than healthy persons which includes radioactive iodine which is easy to measure.  A thyroid scan producing images is typically conducted in connection with the uptake test to allow visual examination of the over-functioning gland.<ref name="Thyrotoxicosis and Hyperthyroidism"/>

Thyroid [[scintigraphy]] is a useful test to characterize (distinguish between causes of) hyperthyroidism, and this entity from thyroiditis. This test procedure typically involves two tests performed in connection with each other: an [[Radioactive iodine uptake test|iodine uptake test]] and a scan (imaging) with a [[gamma camera]]. The uptake test involves administering a dose of radioactive iodine (radioiodine), traditionally [[iodine-131]] (<sup>131</sup>I), and more recently [[iodine-123]] (<sup>123</sup>I). [[Iodine-123]] may be the preferred radionuclide in some clinics due to its more favorable radiation [[dosimetry]] (i.e. less radiation dose to the person per unit administered radioactivity) and a gamma photon energy more amenable to imaging with the [[gamma camera]]. For the imaging scan, I-123 is considered an almost ideal isotope of iodine for imaging thyroid tissue and thyroid cancer metastasis.<ref>{{cite journal | vauthors = Park HM | title = 123I: almost a designer radioiodine for thyroid scanning | journal = Journal of Nuclear Medicine | volume = 43 | issue = 1 | pages = 77–78 | date = January 2002 | pmid = 11801707 | url = http://jnm.snmjournals.org/cgi/content/full/43/1/77 | access-date = 2010-05-10 | url-status = dead | archive-url = https://web.archive.org/web/20081012074621/http://jnm.snmjournals.org/cgi/content/full/43/1/77 | archive-date = 12 October 2008 }}</ref> Thyroid scintigraphy should not be performed in those who are pregnant, a thyroid ultrasound with color flow doppler may be obtained as an alternative in these circumstances.<ref name="Lee 2023" />

Typical administration involves a pill or liquid containing sodium iodide (NaI) taken orally, which contains a small amount of [[iodine-131]], amounting to perhaps less than a grain of salt. A 2-hour fast of no food prior to and for 1 hour after ingesting the pill is required. This low dose of radioiodine is typically tolerated by individuals otherwise allergic to iodine (such as those unable to tolerate contrast mediums containing larger doses of iodine such as used in [[X-ray computed tomography|CT scan]], [[intravenous pyelogram]] (IVP), and similar imaging diagnostic procedures). Excess radioiodine that does not get absorbed into the thyroid gland is eliminated by the body in urine. Some people with hyperthyroidism may experience a slight allergic reaction to the diagnostic radioiodine and may be given an [[antihistamine]].{{citation needed|date=August 2020}}

The person returns 24 hours later to have the level of radioiodine "uptake" (absorbed by the thyroid gland) measured by a device with a metal bar placed against the neck, which measures the radioactivity emitting from the thyroid. This test takes about 4&nbsp;minutes while the uptake % (''i.e.,'' percentage) is accumulated (calculated) by the machine software. A scan is also performed, wherein images (typically a center, left and right angle) are taken of the contrasted thyroid gland with a [[gamma camera]]; a [[radiologist]] will read and prepare a report indicating the uptake % and comments after examining the images. People with hyperthyroid will typically "take up" higher than normal levels of radioiodine. Normal ranges for RAI uptake are from 10 to 30%.

In addition to testing the TSH levels, many doctors test for T<sub>3</sub>, Free T<sub>3</sub>, T<sub>4</sub>, and/or Free T<sub>4</sub> for more detailed results. Free T<sub>4</sub> is unbound to any protein in the blood. Adult limits for these hormones are: TSH (units): 0.45 – 4.50 uIU/mL; T<sub>4</sub> Free/Direct (nanograms): 0.82 – 1.77&nbsp;ng/dl; and T<sub>3</sub> (nanograms): 71 – 180&nbsp;ng/dl. Persons with hyperthyroidism can easily exhibit levels many times these upper limits for T<sub>4</sub> and/or T<sub>3</sub>. See a complete table of normal range limits for thyroid function at the [[thyroid gland]] article.

In hyperthyroidism CK-MB ([[Creatine kinase]]) is usually elevated.<ref>{{cite book | vauthors = Mesko D, Pullmann R | chapter = Blood - Plasma - Serum | veditors = Marks V, Cantor T, Mesko D, Pullmann R, Nosalova G | title = Differential diagnosis by laboratory medicine: a quick reference for physicians. | publisher = Springer Science & Business Media | date = December 2012 | page = 156 | isbn = 978-3-642-55600-5 }}</ref>

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===Subclinical===
{{See also|Symptoms and signs of Graves' disease#Subclinical hyperthyroidism}}
In overt primary hyperthyroidism, TSH levels are low and T<sub>4</sub> and T<sub>3</sub> levels are high. Subclinical hyperthyroidism is a milder form of hyperthyroidism characterized by low or undetectable serum TSH level, but with a normal serum free thyroxine level.<ref>{{cite journal | vauthors = Biondi B, Cooper DS | title = The clinical significance of subclinical thyroid dysfunction | journal = Endocrine Reviews | volume = 29 | issue = 1 | pages = 76–131 | date = February 2008 | pmid = 17991805 | doi = 10.1210/er.2006-0043 | doi-access = free }}</ref> Although the evidence for doing so is not definitive, treatment of elderly persons having subclinical hyperthyroidism could reduce the number of cases of [[atrial fibrillation]].<ref>{{cite journal | vauthors = Surks MI, Ortiz E, Daniels GH, Sawin CT, Col NF, Cobin RH, Franklyn JA, Hershman JM, Burman KD, Denke MA, Gorman C, Cooper RS, Weissman NJ | title = Subclinical thyroid disease: scientific review and guidelines for diagnosis and management | journal = JAMA | volume = 291 | issue = 2 | pages = 228–238 | date = January 2004 | pmid = 14722150 | doi = 10.1001/jama.291.2.228 }}</ref> There is also an increased risk of [[bone fracture]]s (by 42%) in people with subclinical hyperthyroidism; there is insufficient evidence to say whether treatment with antithyroid medications would reduce that risk.<ref>{{cite journal | vauthors = Blum MR, Bauer DC, Collet TH, Fink HA, Cappola AR, da Costa BR, Wirth CD, Peeters RP, Åsvold BO, den Elzen WP, Luben RN, Imaizumi M, Bremner AP, Gogakos A, Eastell R, Kearney PM, Strotmeyer ES, Wallace ER, Hoff M, Ceresini G, Rivadeneira F, Uitterlinden AG, Stott DJ, Westendorp RG, Khaw KT, Langhammer A, Ferrucci L, Gussekloo J, Williams GR, Walsh JP, Jüni P, Aujesky D, Rodondi N | title = Subclinical thyroid dysfunction and fracture risk: a meta-analysis | journal = JAMA | volume = 313 | issue = 20 | pages = 2055–2065 | date = May 2015 | pmid = 26010634 | pmc = 4729304 | doi = 10.1001/jama.2015.5161 }}</ref>

A 2022 meta-analysis found subclinical hyperthyroidism to be associated with cardiovascular death.<ref>{{cite journal |last1=Müller |first1=P |last2=Leow |first2=MK |last3=Dietrich |first3=JW |title=Minor perturbations of thyroid homeostasis and major cardiovascular endpoints-Physiological mechanisms and clinical evidence. |journal=Frontiers in Cardiovascular Medicine |date=2022 |volume=9 |pages=942971 |doi=10.3389/fcvm.2022.942971 |pmid=36046184|pmc=9420854 |doi-access=free }}</ref>

===Screening===
In those without symptoms who are not pregnant there is little evidence for or against screening.<ref>{{cite journal | vauthors = LeFevre ML | title = Screening for thyroid dysfunction: U.S. Preventive Services Task Force recommendation statement | journal = Annals of Internal Medicine | volume = 162 | issue = 9 | pages = 641–650 | date = May 2015 | pmid = 25798805 | doi = 10.7326/m15-0483 | s2cid = 207538375 }}</ref>