[Iodine and thyroid hormones]

In the years 1995-2002, a survey was conducted involving 5 263 individuals (2 276 males, 2 987 females) between the ages of 6-98. They were selected randomly from the central registery in 7 counties in the Czech Republic. The level of urinary iodine in these individuals was established using the Sandell-Kolthoff rection which was preceded by the alkaline ashing of the samples as follows: (n = 5 263), thyroglobulin (TG, n = 3 902), thyrotropin(TSH, n = 5 162) freee thyroxin (fT4, n = 5 160) and free triiodothyronine (fT3, n = 4 931), where the thyroid hormones, TSH, and TG were determined in serum using immunoassays. The individuals were divided into groups according to their iodine deficiency, i.e. to the group with urinary iodine concentration < 50, 50-100, 100-200, and > 200 microg I/l of urine. In these groups the mean and median of TG, TSH, fT4, and fT3 were calculated. The means and medians of TG and fT4 increased with the decrease of urinary iodine, and conversely TSH decreased with the decrease of urinary iodine. The values of fT3 were relatively unaffected by the changes in the concentrations of urinary iodine. All the hormonal changes fell into the normal reference rang. It is evident from our results that in cases iodine deficiency in the organism, there is a tendency to raise the sensitivity thyrocytes to TSH stimulation rather than a rise in the concentration of circulating TSH. Of all the hormones observed, thyroglobulin was the best indicator of iodine retention in the organism.