Iodine is a fundamental substance for the correct development of our body, being the main compound used in the production of thyroid hormones.
There are some iodine isoforms that are used in medicine for diagnostic and therapeutic purposes. The Iodine 131 for example it is a radioactive isotope of iodine, used both as a therapy for some types of hyperthyroidism, and as a tracer substance during thyroid scintigraphy.
In fact, Iodine 131 is administered orally, fasting, and is then absorbed in the intestine, and transported by the blood to the thyroid, where it is concentrated. Obviously, the greater the activity of the thyroid, the greater the absorption and concentration of radioiodine.
Furthermore, the nature of some thyroid nodules can be better elucidated by analyzing how they concentrate it Radioactive iodine, differentiating into "hot" nodules, with a high concentration of iodine, and "cold" nodules, with low uptake.
Iodine 131 is most frequently used in the dose of 5-10 microCi. It has a half-life of the blood dose (half-life) of 8 days.
At constant intervals of time from administration, generally after 3, 6 or 24 hours, the radioactivity present in the thyroid is measured by means of a suitable instrument, expressed as a percentage of the administered radioactivity.
In some cases, in the judgment of the radiologist or nuclear medicine doctor, potassium perchlorate may be administered for premedication purposes.
Normal thyroid uptake values for Iodine 131 are generally between 10-40% at the 6th hour after the administration of radioiodine, and between 13-60% after 24 hours after administration.
It is obvious that before carrying out this type of examination, the attending physician or radiologist should be informed about the possible intake of drugs or compounds (also for topical use, i.e. on the skin, such as disinfectants) containing iodine, as well as the possible administration of iodinated radiography contrast media in previous diagnostic tests, as in these cases the test could be distorted.
Increased thyroid iodine uptake
- Primary hyperthyroidism
- Hypothyroidism due to defective hormonogenesis
- Ectopic TSH syndrome
- Diet deficient in iodine
- Taking estrogen
- Taking anticonvulsant drugs
- Nephrotic syndrome and acute renal failure
- Chronic liver disease or cirrhosis
- Gigantism and acromegaly
Increased radioiodine uptake greater than 12%
- Graves' disease
- Plummer's adenoma
- TSH secretion pituitary adenoma
- Silent lymphocytic thyroiditis
- Trophoblast tumor
- Thyrotropin productive neoplasm:
- vesicular mola
- embryonic tumors of the testis
Decreased thyroid iodine uptake
- Primary and secondary hypothyroidism (excluding forms of defective hormonogenesis)
- Antithyroid drugs:
- perchlorate ions,
- thiocyanate and pertechnetate
- Other drugs:
- paraminosalicylic acid,
- vitamin A,
- Thyroid hormones (due to the feedback exerted on the thyroid, as well as their iodine content)
- Other hormones:
- Goitogenic foods:
- brassicaceae (cabbage, broccoli, turnips, savoy cabbage) containing thiocyanate
- milk from cattle fed with brassicas
- Chronic renal failure.
Decrease> 3% of thyroid radioiodine uptake
- Thyrotoxicosis induced by the assumption of T3 or T4 (in this situation the administration of TSH can be used to facilitate the diagnosis, since it would increase the thyroid uptake of Iodine 131 by 50% in the normal subject)
- Iodine-induced hyperthyroidism (in this case the administration of TSH not determines the normal approximately 50% increase in iodine uptake; urinary iodine is greater than 2000 pg / 24 hours)
- Graves' disease with excess iodine
- Subacute thyroiditis
- Silent lymphocytic thyroid (again TSH administration does not cause the normal increase in iodine uptake)
- Ectopic hyperthyroidism
- Functional metastatic thyroid cancer (again TSH administration does not cause the normal increase in iodine uptake)
- Ectopic hyperthyroidism
- Ovarian struma (TSH administration does not cause the normal increase (50%) in iodine uptake).