[Immunoradiometric measurement of serum thyrotropin levels in inhabitants who used iodized salt for 25 years in an endemic goiter area].

Recently we surveyed the thyroid function and TSH concentration of villagers in an endemic goiter area where iodized salt had been supplied for 25 years. We found that the serum FT3 and TSH (IRMA) level of villagers were higher and the FT4 level was lower than those of the controls, comparing with the RIA, which suggested that the inhabitants of the endemic goiter area had subclinical hypothyroidism based on the IRMA method for TSH assay. Therefore, we suggest that the best biochemical technique for monitoring the iodized salt prophylaxis program and the physiological response of villagers to iodine is measurement of serum TSH level with the ultrasensitive assay and FT4 level periodically.