Kinetics of acute and chronic iodine excess

Abstract

Iodine plays an important role in thyroid physiology resulting from its importance as a requisite substrate for the synthesis of thyroid hormones and from its action as a regulator of thyroid function. Following intestinal absorption, inorganic iodide is largely confined to the extracellular fluid. Serum concentrations of inorganic iodide well reflect the amount of iodine present in the extracellular compartment. Since serum inorganic iodide levels are important determinants of thyroid iodine uptake, serum iodide measurement offers a valuable tool for the investigation of many basic and clinical aspects of thyroid iodine metabolism. Here we summarize important aspects of iodine metabolism and focus selectively on technical aspects of serum inorganic iodide measurement and on the kinetics of inorganic iodide in various states of iodine excess. Presently, paired-ion, reversed-phase HPLC with electrochemical detection is obviously the best method for measurement of serum inorganic iodide being highly sensitive, easy to perform, and almost completely insensitive to interfering substances. Using this method, we could demonstrate an acute increase of serum inorganic iodide during the administration of large amounts of iodide as Lugol's solution given preoperatively in patients with Graves' hyperthyroidism. In patients under treatment with the iodine containing drug amiodarone (n=37), serum inorganic iodide levels were highly elevated (range 3.5-208.2 microg/dl, median 36.6 microg/dl). Serum concentrations of inorganic iodide were correlated neither to the daily amiodarone dose, nor to the serum levels of amiodarone.

Relationship between estimated glomerular filtration rate and biological half-life of 131I

“…In particular, the elimination occurred via free glomerular filtration, with no secretion and virtually no resorption. These results matched the known kinetic data of Saller and Cavalieri (3,26).…”

“…The renal function strongly influences the iodine excretion (3,26), and a reduced radioiodine elimination may result in increased retention (▶ Fig. 3).…”

“…Given that 95% of iodine is eliminated via the kidneys (26) it can be assumed that patients with renal insufficiency are at increased risk of longer retention of 131 I, and consequently of increased radiation exposure and radiotoxicity, especially in blood and bone marrow (6,20,24).…”

Research needs for assessing iodine intake, iodine status, and the effects of maternal iodine supplementation

“…Serum thyroglobulin has shown promise as a biomarker of iodine status; further assessment of its usefulness for this purpose would require the validation of assay-specific thyroglobulin reference ranges, particularly for pregnant women (categorized by trimester) and neonates (29). Serum inorganic iodide may also be worthy of investigation (32). Together with the identification of useful biomarkers, there is a need for the development and validation of analytical methods that are accurate, precise, and reliable.…”

A cAse of thyreotoxicosis following coronAry AngyogrAphy (clinical observation)

“…В течение жизни человек потребляет всего 2-3 г йода, в то время как во время проведения коронарной ангиографии доза вводимого парентерально йода составляет 25-52 г [2]. Такой выраженный прирост концентрации йодида в плазме крови объясняется не только содержанием в РКС неорганического йода, но и эндогенным отщеплением свободного йода [5,6]. Лица, не имеющие заболеваний щитовидной железы в анамнезе, как правило, сохраня-ют толерантность к приему больших доз йода и у них сохраняется эутиреоз.…”