Radioactive iodine uptake test

{{Short description|Diagnostic test for causes of hyperthyroidism}}

{{redirects|RAIU}}

{{Infobox diagnostic |

Name = Radioactive iodine uptake test |

Image = Thyroid scan.jpg |

Caption = Thyroid scan with Iodine-123 for evaluation of hyperthyroidism. |

ICD10 = |

ICD9 = {{ICD9proc|92.01}} |

MeshID = |

OPS301 = {{OPS301|3-701}} |

Synonyms = RAIU test|

}}

The radioactive iodine uptake test is a type of scan used in the diagnosis of thyroid problems, particularly hyperthyroidism. It is entirely different from radioactive iodine therapy (RAI therapy), which uses much higher doses to destroy cancerous cells. The RAIU test is also used as a follow-up to RAI therapy to verify that no thyroid cells survived, which could still be cancerous.[http://www.thyca.org/rai.htm] ThyCa: Thyroid Cancer Survivors' Association, Inc., Radioactive Iodine (RAI).

The patient swallows a radioisotope of iodine in the form of capsule or fluid, and the absorption (uptake) of this radiotracer by the thyroid is studied after 4–6 hours and after 24 hours with the aid of a scintillation counter. The dose is typically 0.15–0.37 MBq (4–10 μCi) of ¹³¹I iodide, or 3.7–7.4 MBq (100–200 μCi) of ¹²³I iodide.{{Cite book|last1=Kwee|first1=Sandi A.|last2=Coel|first2=Marc N.|last3=Fitz-Patrick|first3=David|year=2007|page=172|title=Iodine-131 Radiotherapy for Benign Thyroid Disease|journal=Nuclear Medicine Therapy|editor1-last=Eary|editor1-first=Janet F.|editor2-last=Brenner|editor2-first=Winfried|publisher=CRC Press|isbn=978-0-8247-2876-2}} The RAIU test is a reliable measurement when using a dedicated probe with a reproducibility of 1 percent and a 95%-least-significant-change of 3 percent.{{Cite journal|last1=Pelletier-Galarneau|first1=Matthieu|last2=Martineau|first2=Patrick|last3=Klein|first3=Ran|last4=Henderson|first4=Matthew|last5=Zuckier|first5=Lionel S.|date=January 2018|title=Reproducibility of radioactive iodine uptake (RAIU) measurements|journal=Journal of Applied Clinical Medical Physics|volume=19|issue=1|pages=239–242|doi=10.1002/acm2.12217|issn=1526-9914|pmc=5768031|pmid=29165912}}

The normal uptake is between 15 and 25 percent, but this may be forced down if, in the meantime, the patient has eaten foods high in iodine, such as dairy products and seafood.M. Sara Rosenthal. The Thyroid Sourcebook. McGraw-Hill, 2008. Page 140. Low uptake suggests thyroiditis, high uptake suggests Graves' disease,[http://www.webmd.com/a-to-z-guides/radioactive-iodine-uptake-test WebMD article] on RAIU test. and unevenness in uptake suggests the presence of a nodule.{{citation needed|date=July 2017}}

¹²³I has a shorter half-life than ¹³¹I (a half day vs. 8.1 days), so use of ¹²³I exposes the body to less radiation, at the expense of less time to evaluate delayed scan images.{{cite book|last1=Ain|first1=Kenneth|last2=Rosenthal|first2=M. Sara|title=The Complete Thyroid Book, Second Edition|url=https://books.google.com/books?id=TyN9y7ZlBVsC&pg=PT57|access-date=18 July 2011|date=2010-08-19|publisher=McGraw-Hill Professional|isbn=978-0-07-174348-8|pages=57–}} Furthermore, ¹²³I emits gamma radiation, while ¹³¹I emits gamma and beta radiation.{{cite book|last=Pilling|first=Gwen|title=Salters higher chemistry|url=https://books.google.com/books?id=RiM4plecZw0C&pg=PA132|access-date=18 July 2011|date=1999-06-24|publisher=Heinemann|isbn=978-0-435-63098-0|pages=132–}}

__TOC__