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Objective: To investigate the current status of iodine nutrition and the prevalence of thyroid diseases in Guiyang, a mild iodine deficiency city practiced salt iodization for 25 years., Methods: A representative sample of 1509 adults aged 20 years old or above in Guiyang, selected by a multistage stratified sampling method, participated in the study. After an overnight fasting, serum thyroid hormones, serum thyroid autoantibodies, and urine iodine were measured. B-mode ultrasonography of the thyroid was performed in the population. Meanwhile, urine iodine of 80 children aged 8 - 10 years old in the same community were measured after an overnight fasting., Results: The median of 8-10 years old children's urinary iodine was 228.7 µg/L. The prevalence of overt hypothyroidism, subclinical hypothyroidism, overt hyperthyroidism and subclinical hyperthyroidism was 1.79%, 14.12%, 1.52% and 1.06% respectively. The prevalence of subclinical hypothyroidism was significantly higher than overt hypothyroidism (P < 0.05) and was significantly higher in female than that in male (P < 0.05). The prevalence of positive thyroid peroxidase antibody, positive thyroglobulin antibody and autoimmune thyroiditis was 14.38%, 13.59% and 4.44% respectively, which were significantly higher in female than that in male (all P values < 0.05). The prevalence of diffuse goiter and nodular goiter was 0.86% and 0.20% respectively, with a significant difference (P < 0.05)., Conclusion: After 25 years of salt iodization, the iodine nutrition in Guiyang is more than adequate with high prevalence of overt hypothyroidism, subclinical hypothyroidism and autoimmune thyroiditis.

Objective: To determine the factors that influence the development of abnormal thyrotropin (TSH) level in an euthyroid population., Methods: We conducted a follow-up study in 3 communities with different iodine status. Of the 3403 euthyroid subjects at baseline screened in 1999, 80.1% (n = 2727) was visited and sampled in 2004 for measuring TSH, thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb)., Results: Iodine status in the 3 communities were stable. Decreased TSH level (< 0.3 mU/L) developed in 2.5% (n = 68) of sampled subjects, while raised TSH level (> 4.8 mU/L) in 2.4% (n = 64). A logistic analysis showed that risk factors for developing decreased TSH level included positive conversion of TPOAb (OR = 5.5), positive TPOAb both in 1999 and in 2004 (OR = 4.0), positive TgAb in 2004 (OR = 3.7) and TSH < 1.0 mU/L in 1999 (OR = 2.6). Risk factors involved in developing raised TSH level included iodine status of Zhangwu community (OR = 4.1), iodine status of Huanghua community (OR = 3.9), positive TgAb in 2004 (OR = 3.7), positive TPOAb both in 1999 and 2004 (OR = 3.6), positive conversion of TPOAb (OR = 2.7) and TSH > 1.9 mU/L in 1999 (OR = 2.6)., Conclusions: Exposure to long-term iodine excess imposes danger of developing hypothyroidism. The risk will be even higher when exposing to iodine adequacy after correction of iodine deficiency. An interval between 1.0 and 1.9 mU/L of TSH level was optimal with the least probability of developing abnormal TSH level.

Objective: To establish a method of ion chromatography for urine iodide determination and evaluate its application in epidemiological studies., Methods: Urinary iodine was determined using ICS-2500 ion chromatography coupled with IonPac AS7 analytical column (4 mm x 250 mm), silver electrode and direct current amperometry for 467 elderly subjects (above 50 years) with their urinary Tsh and FT4 also determined. The history of thyroid diseases was examined among these subjects., Results: The peak area of the ion chromatography was linearly correlated with urinary iodine concentration, with the correlation coefficient of 0.9999. The detection limit of iodide was around 3.5 microg/L (S/N=3), with coefficients of variation ranging from 3.16% to 3.45% and mean recovery rate of 95%. The urinary iodine level in the 467 elderly subjects showed a positively skewed distribution with the median level of 224.7 microg/L., Conclusion: Ion chromatography for urinary iodine determination has excellent selectivity, sensitivity, reliability, accuracy and stability, and may ensure satisfactory effect for application in epidemiological studies.

Objective: To evaluate the impact of universal salt iodization using monitoring data on correctional status of iodine deficiency and hospitalized thyroid diseases., Methods: Retrospective survey was conducted to collect medical records of hospitalized thyroid disease cases. Routine monitoring data on population iodine nutrition status and goiter prevalence were analyzed., Results: The coverage of adequately iodized salt was consistently above 95%. Hospitalization rate of thyroid diseases rose steadily, and peaked at 54.5 per 100,000. The proportion of hospitalized thyroid disease among hospitalized diseases also rose with female and those aged above 40 years old mostly affected. The proportion of hospitalized hyperthyroidism among total hospitalized thyroid disease rose from 13.6% to 34.7%., Conclusions: Universal salt iodization might eliminate iodine deficiency while other impact still exists. However, the benefits of universal salt iodization should be far overweight the adverse effects.