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A radioisotope of iodine that emits beta and gamma rays, has a half-life of 8.05 days, and is used as a tracer in thyroid studies and as therapy in hyperthyroidism and thyroid cancer.


(i'o-din?, -den?) [Gr. ioeides, violet-colored + -ine] I
A nonmetallic chemical element of the halogen group, atomic weight (mass) 126.904, atomic number 53, specific gravity (solid, 20°C) 4.93. It is a black crystalline substance with a melting point of 113.5°C; it boils at 184.4°C, giving off a characteristic violet vapor. Sources of iodine include vegetables, esp. those growing near the seacoast; iodized salt; and seafoods, esp. liver of halibut and cod, or fish liver oils.
CAS # 7553-56-2


Iodine is part of the hormones triiodothyronine (T3) and thyroxine (T4), and prevents goiter by enabling the thyroid gland to function normally. The amount of iodine in the entire body averages 50 mg, of which 10 to 15 mg is found in the thyroid. The adult daily requirement for iodine is from 100 to 150 µg. Growing children, adolescents, pregnant women, and those under emotional strain need more than this amount of iodine.

Deficiency Symptoms

Iodine deficiency in the diet may lead to simple goiter characterized by thyroid enlargement and hypothyroidism. In young children, this deficiency may result in retardation of physical, sexual, and mental development, a condition called cretinism.


131I See: radioactive iodine

protein-bound iodine

Abbreviation: PBI
Iodine that is attached to serum protein. In the past, thyroid function was tested with a serum measurement of PBI.

radioactive iodine

Any of the radioactive isotopes of iodine, esp. iodine-131, used in diagnosis and treatment of thyroid disorders and in the treatment of toxic goiter and thyroid carcinoma.
See: radioiodine

tincture of iodine

See: tincture


a chemical element, atomic number 53, atomic weight 126.904, symbol I. See Table 6. Iodine is essential in nutrition, being especially prevalent in the colloid of the thyroid gland. It is used in the treatment of hypothyroidism and as a topical antiseptic. Iodine is a frequent cause of poisoning. See also iodism.

a radioisotope of iodine having a half-life of 60 days and a principal gamma-ray photon energy of 28 keV; used as a label in radioimmunoassays and other in vitro tests, and also for thyroid imaging. Symbol 125I.
a radioisotope which concentrates in chromaffin cells; used in diagnostic scintigraphy, e.g. in cases of pheochromocytoma.
a radioisotope of iodine having a half-life of 8.1 days and a principal gamma-ray photon energy of 364 keV; used in treatment of hyperthyroidism and carcinoma of the thyroid, in thyroid function testing, and in imaging of the thyroid gland and other organs. Symbol 131I.
iodine deficiency
may occur in all species under certain conditions; in dogs and cats, a factor in all-meat diets. See also goiter.
iodine contrast agents
iodine salts are opaque to x-rays; therefore they can be combined with other compounds and used as contrast media in diagnostic x-ray examinations.
iodine nutritional deficiency
is characterized by goiter, neonatal mortality and alopecia.
iodine poisoning
occurs usually due to accidental overdosing. It causes lacrimation, anorexia, coughing due to bronchopneumonia, and a heavy dandruff. Paradoxically, iodine excess may result in thyroid hyperplasia and goiter, especially in the young.
protein-bound iodine
a test of thyroid function. See also protein-bound iodine (PBI) test.
radioactive iodine
see iodine-125, iodine-131 (above).
iodine residues in milk
careless use of iodine-based teat dips results in unacceptable residues of iodine in milk.
iodine solution
contains 2% free iodine and 2.4% sodium iodide in an aqueous solution.
iodine solution (strong)
contains 5% free iodine and 10% potassium iodide in an aqueous solution.
tamed iodine
iodine trapping
the selective absorption of iodine from the circulation by the thyroid gland.
References in periodicals archive ?
This is the first new formulation of Sodium Iodide I-131 available to the Nuclear Medicine community in over 20 years," said Dr.
En el caso del I-131, la utilización de delantales plomados no es práctico, dado que el espesor necesario de plomo es muy elevado para conseguir un nivel de protección adecuado (se requiere un espesor de plomo de 3 mm para conseguir reducir la exposición a la mitad) y el peso del delantal resultaría excesivo, por dicho motivo hay que procurar mantenerse a la distancia más alejada posible, reducir el tiempo de exposición y hacer uso de mamparas plomadas móviles.
The bioassay feature allows the system to be used to measure staff thyroid burden for I-123, I-125, and I-131.
Azedra is a small molecule, targeted radiotherapeutic based on the known I-131 MIBG molecule produced with Molecular Insight's proprietary Ultratrace technology.
All known tumors had good uptake of I-131 in 45% of the patients aged 70 and older and in 66% of those younger than 60.
In case of Tg detection within 1 year after radioiodine therapy, no evidence of disease was defined as a negative diagnostic or posttherapy I-131 whole-body scan or undetectable Tg after discontinuation of thyroid hormone treatment.
Unprocessed milk was likely to have been consumed more quickly after milking, and half of the radioactivity associated with I-131 disappears every 8 days.
Because of its 97% success rate and very low risk of side effects, Radioiodine I-131 treatment has become the treatment of choice for veterinarians worldwide.
I-131 was reported in only one prefecture and Cs-137 was reported in three prefectures, with a value of 4.
1-cm lesion in the posterior segment of the right hepatic lobe, which correlated to the area of uptake on the I-131 whole-body scan.
This patient had a positive I-131 scan, along with an 18F-FDG PET/CT scan that showed increased metabolic activity within the thyroid bed approximately 6 months after surgery.
The diagnosis of severe thyrotoxicosis also required radioactive iodine (I-131) uptake that exceeded 30% at 4 or 24 hours after the administration of I-131.