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In healthy people, high serum antithyroid antibody concentrations are associated with high serum thyrotropin concentrations and thyroid enlargement

(July 2005)

The background of the study. High serum concentrations of antithyroid peroxidase (anti-TPO) or antithyroglobulin (anti-Tg) antibodies are the hallmark of autoimmune thyroid disease. Thyroid function may be normal or low, and the thyroid gland may be enlarged or small. The relationships between thyroid antibodies, size, and function were studied in a large group of people in Denmark.

How the study was done. The group consisted of 4168 people living in two regions of the country. Thyroid volume was measured by ultrasonography (normal, 6.6 to 14.9 ml). Serum thyrotropin (TSH) (normal, 0.4 to 3.6 mU/L), anti-TPO antibodies, and anti-Tg antibodies also were measured.

The results of the study. The thyroid gland was small in 5 percent of the subjects, normal in 60 percent, and large in 35 percent. Serum TSH concentrations were low in 5 percent, normal in 91 percent, and high in 4 percent.

Overall, serum anti-TPO, anti-Tg antibodies, or both were detected in 19 percent of the subjects. One or both antibodies were detected in 18 percent of those with low serum TSH concentrations, 17 percent of those with normal concentrations, and 65 percent of those with high concentrations.

Among the subjects with high serum TSH concentrations, one or both serum antibodies were detected in 91 percent of those who had a large thyroid, 62 percent of those with a normal-sized thyroid, and 44 percent of those with a small thyroid. In contrast, among the subjects with normal or low serum TSH concentrations, there was no relationship between serum anti-TPO or anti-Tg antibodies and thyroid volume.

The conclusions of the study. Among healthy subjects, the presence of serum antithyroid antibodies is associated with increasing serum TSH concentrations, and with thyroid enlargement in those with high serum TSH concentrations.

The original article. Bulow Pedersen I, Laurberg P, Knudsen N, Jorgensen T, Perrild H, Ovesen L, Rasmussen LB. A population study of the association between thyroid autoantibodies in serum and abnormalities in thyroid function and structure. Clin Endocrinol (Oxf) 2005;62:713-20.

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Autoimmune Thyroid Disease