To maintain normal level of thyroid hormone, especially for free thyroxine (FT4), individuals with latent thyroid gland damage might have required higher thyroid stimulating hormone (TSH) than those without latent thyroid gland damage. Anti-thyroid peroxidase antibody (TPO-Ab) is a main cause of auto-immune thyroiditis, and therefore euthyroid individuals positive for TPO-Ab might have latent damage to the thyroid gland. Therefore, the association between TSH values and TPO-Ab positivity may be useful to determine the influence of latent thyroid gland damage on requirement of TSH. Furthermore, because latent damage of thyroid might elevate TSH level but not FT4 level, those associations should be observed independent from FT4. This cross-sectional study analyzed 1431 Japanese with normal ranges of free triiodothyronine (FT3) and FT4. Since TPO-Ab is associated with atherosclerosis in euthyroid individuals, cardiovascular risk factors might underlie the association between TPO-Ab and TSH values. After adjusting for FT4 and known cardiovascular risk factors, the adjusted odds ratio (95% confidence interval) of TPO-Ab positivity for logarithmic value of TSH was 1.53 (1.20, 1.95). Essentially the same association was observed when the analysis was restricted to individuals without subclinical hypothyroidism (1.54 [1.15, 2.13]). Euthyroid individuals with latent thyroid gland damage might have increased the requirement of TSH.
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