A publication of the American Thyroid Association

Summaries for Patients from Clinical Thyroidology by Ernest Mazzaferri, MD MACP
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Abbreviations & Definitions

TPOAb Serum anti-thyroid peroxidase antibodies

TgAb Anti-thyroglobulin antibodies

TSH Thyroid-stimulating hormone (thyrotropin)

Thyroiditis An inflammatory thyroid disorder that is affected by anti-thyroid antibodies that can lead to thyroid failure

Panshan A Chinese city with mild iodine deficiency.

Zhangwu A Chinese city with adequate iodine intake.

Huanghua A Chinese city with excessive iodine intake

U.S. Urinary iodine concentrations This is a reflection of iodine intake. Median urinary iodine level in 1971–74 was 320 and in 2000 has decline to 161 μg/L (NHANES III)

What is the study about? Autoimmune thyroid failure is higher than usual among thyroid antibody-positive individuals on an excessively high iodine diet

The full article title: Antithyroperoxidase and antithyroglobulin antibodies in a five-year follow-up survey of populations with different iodine intakes.” It is in the February 2008 Issue of the journal of Clinical Endocrinology and Metabolism (volume 93 Issue 5, pages 1751-57) The authors are Y Li, D Teng, Z Shan, X Teng, H Guan, X Yu, C Fan, W Chong, F Yang, H Dai H, X Gu, Y Yu, J Mao, D Zhao, JLi, Y Chen, R Yang C Li, W Teng.

What is known about the problem being studied? Blood levels of anti-thyroid antibodies correlate with the severity of chronic thyroid lymphocytic infiltration, which may cause thyroiditis, regardless of the presence or absence of hypothyroidism. However, the function and progression of these antibodies remains uncertain.

What was the aim of the study? This study was aimed at identifying the natural progression of antithyroid antibodies and clinical hypothyroidism in areas with substantially differing iodine uptake.

Who was studied? A total of 16,287 Individuals living in three rural areas in northern China with differing iodine intake (see Box) volunteered to undergo thyroid studies

How was the study done? Baseline specimens were collected for urine iodine levels, serum TSH, TPOAb, and TgAb levels. In 2004, 80% of this group underwent followup studies using the same protocol except for the addition of neck ultrasound studies.

What were the results of the study? Initially, most subjects had normal thyroid function and only a few (~9%) had antibodies. The prevalence of antibodies was greater among women than among men and increased with age, especially in women. After 5 years, the rate of elevated TSH levels (>4.8 mIU/L) was higher in those with anti-thyroid antibodies and was higher in areas of increased iodine intake: 5.3% in Panshan, 14.3% in Huanghua, and 23.4% in Huanghua (see Box).

How does this compare with other studies? These results confirm and add to those of the Whickham Survey, which also examined the natural history of individuals with baseline thyroid autoimmunity

What are the limitations of this study? There was a small loss of subjects when from the baseline to the follow-up study; however, the numbers were small and likely did not seriously affect the study

What are the implications of this study? Patients with anti-thyroid antibodies, especially women, develop thyroid failure more often than people without these antibodies. An excessive iodine intake also increases the risk for developing hypothyroidism.

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