Iodine is required in small amounts by humans, the current RDA being 150 micrograms per day; the only known function of iodine in man is as a component of the secretions of the thyroid gland, principally tri-iodothyronine and thyroxine. Iodine is one of the halogen series of elements (along with fluorine, chlorine and bromine); it was formerly used as an antiseptic, but is now regarded as too toxic for that purpose.
80 - 90% of the total serum iodine is incorporated into thyroxine, which is largely protein bound; the remainder (5 - 15%) of the serum iodine is in the form of iodide (the plasma inorganic iodide) and it is this fraction that is filtered at the glomerulus and passes into the formed urine. Regulation of body iodine does not occur via changes in the glomerular filtration rate (as occurs with other essential elements) but via iodine uptake into the thyroid gland.
A common method for correction of iodine deficiency is salt iodization - the addition of potassium iodate to salt for human and livestock consumption to give a concentration of c. 15 ppm of iodine - with the urinary iodine concentration as the principal indicator of effect. Measurement of thyroid size has a more limited role as an indicator because it reflects chronic rather than immediate iodine deficiency.
Urine creatinine can be co-analysed with iodine to correct for urine dilution in a short collection (6 hours, early morning urine or random urine collection). Expressed in this way, the reference interval for urine iodine is 0.16 - 0.42 mmol/mol creatinine .
Patients should avoid iodine containing food supplements, fish & seafood and iodised (sea) salt for at least 48 hours prior to providing a random, mid-stream, urine specimen.
Postal samples should reach Biolab within 48 hours of collection
The urine iodine concentration is recommended as the best single indicator of iodine nutrition, with the following stratification of reference values :
iodine.pdf (Click to Download)
rep-iodine.pdf (Click to Download)
A 24 hour urine collection with an accurate total volume is the preferred sample; alternatively, a 6 hour collection, an early morning urine or a random urine sample can be supplied.
Postal Samples Acceptable:
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