Significance of prediagnostic thyroid antibodies in women with autoimmune thyroid disease

Introduction: Antibodies to thyroglobulin (Tg), thyroperoxidase (TPO), and TSH receptor (TSH-R) are prevalent in autoimmune thyroid diseases. We aimed to assess whether females with Graves disease or Hashimoto thyroiditis are more likely than age-matched controls to have thyroid antibodies before clinical diagnosis and to measure the timing of antibody seroconversion. Methods: This was a nested case-control study using the Department of Defense Serum Repository and the Defense Medical Surveillance System, 1998-2007. We assessed thyroid antibodies in the serum of 522 female, active-duty, military personnel including: 87 Graves disease cases, 87 Hashimoto thyroiditis cases, and 348 age matched controls. One serum sample was available at the time of the clinical diagnosis (±6 months); three additional samples were retrieved from the repository up to 7 yr before the clinical diagnosis, for a total of 2088 samples. Results: In Hashimoto thyroiditis, TPO antibodies were found in about 66% of the cases at all time points. Tg antibodies showed a similar stationary trend, at a lower prevalence of about 53%at all time points. No TSH-R antibodies were found. In Graves disease, TPO antibodies gradually increased from 31% at 5-7 yr prior to diagnosis to 57% at diagnosis and Tg antibodies from 18 to 47%. TSH-Rantibodies were present before diagnosis and showed an increasing prevalence from 2, 7, 20, to 55%. Conclusions: Antibodies to Tg, TPO, and TSH-R precede by years the development of the diagnostic autoimmune thyroid diseases phenotype. Overall, the presence of thyroid antibodies in apparently healthy individuals should not be neglected.