The radioactive iodine uptake test is a type of scan used in the diagnosis of

thyroid The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobes. The lower two thirds of the lobes are connected by a thin band of tissue called the thyroid isthmus. The ...

problems, particularly

hyperthyroidism Hyperthyroidism is the condition that occurs due to excessive production of thyroid hormones by the thyroid gland. Thyrotoxicosis is the condition that occurs due to excessive thyroid hormone of any cause and therefore includes hyperthyroidis ...

. 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.
ThyCa: Thyroid Cancer Survivors' Association, Inc., Radioactive Iodine (RAI). The patient swallows Isotopes of iodine#Notable radioisotopes, a radioisotope of

iodine Iodine is a chemical element with the Symbol (chemistry), symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , ...

in the form of capsule or fluid, and the absorption (uptake) of this

radiotracer A radioactive tracer, radiotracer, or radioactive label is a chemical compound in which one or more atoms have been replaced by a radionuclide so by virtue of its radioactive decay it can be used to explore the mechanism of chemical reactions by tr ...

by the thyroid is studied after 4–6 hours and after 24 hours with the aid of a

scintillation counter A scintillation counter is an instrument for detecting and measuring ionizing radiation by using the excitation effect of incident radiation on a scintillating material, and detecting the resultant light pulses. It consists of a scintillator wh ...

. The dose is typically 0.15–0.37

MBq ''MBQ'' is an original English-language manga created by Tokyopop's Rising Stars of Manga second-place winner Felipe Smith. ''MBQ'' is an expansion of his second-place winning entry in the third Rising Stars competition. It is the story of a y ...

(4–10 μCi) of ¹³¹I iodide, or 3.7–7.4 MBq (100–200 μCi) of ¹²³I iodide. 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. 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

, such as dairy products and seafood.M. Sara Rosenthal. ''The Thyroid Sourcebook.'' McGraw-Hill, 2008. Page 140. Low uptake suggests

thyroiditis Thyroiditis is the inflammation of the thyroid gland. The thyroid gland is located on the front of the neck below the laryngeal prominence, and makes hormones that control metabolism. Signs and symptoms There are many different signs and sympto ...

, high uptake suggests

Graves' disease Graves' disease (german: Morbus Basedow), also known as toxic diffuse goiter, is an autoimmune disease that affects the thyroid. It frequently results in and is the most common cause of hyperthyroidism. It also often results in an enlarged thyro ...

,WebMD article
on RAIU test. and unevenness in uptake suggests the presence of a nodule. ¹²³I has a shorter

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ...

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. Furthermore, ¹²³I emits

gamma radiation A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically s ...

, while ¹³¹I emits gamma and

beta radiation A beta particle, also called beta ray or beta radiation (symbol β), is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay. There are two forms of beta decay, β� ...

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Contraindications

The test is inappropriate for patients who are pregnant or breastfeeding.

Additional images

File:Thyroid scintigraphy.jpg, Thyroid scintigraphy LMP BNUKSEA 4000+60000

References

{{Medical imaging Nuclear medicine Thyroid disease Thyroidological methods