Anti-Thyroperoxidase Antibody Levels >500 IU/ml Indicate a Moderately Increased Risk for Developing Hypothyroidism in Autoimmune Thyroiditis.

Autoimmune Thyroiditis (AIT) is the most common autoimmune disease, which is characterized by cellular and humoral immunity leading to thyroid destruction. The impact of the humoral immunity on the risk to develop hypothyroidism has not exactly been defined yet. The aim of the present study was to investigate the association between thyroid antibody levels and the risk for developing hypothyroidism. In this retrospective study, 335 untreated AIT patients were enrolled. Anti-thyroperoxidase (TPO) antibodies, anti-thyroglobulin (Tg) antibodies (Abs), and the TSH level were measured. Patients with TPO-Ab levels>500 IU/ml showed a moderately increased risk of having elevated TSH levels [p=0.0023; relative risk (95% confidence interval): 1.343 (1.108-1.627)] compared to those below this threshold. AIT patients with TPO- or Tg-Abs<100 IU/ml and between 100-500 IU/ml had no significantly different TSH levels. Presence of Tg-Abs alone or in combination with TPO-Abs did not help to increase the sensitivity to identify patients at risk. Long term follow-up of AIT patients with high TPO-Abs level (>500 IU/ml) showed an increase of TSH levels (mean: 0.5 mIU/l; range: 2.52±2.73 to 3.02±3.05 mIU/l; p=0.0420). Still, these patients remained euthyroid. Our data indicate largely elevated levels of TPO-Abs being associated with a moderately increased risk of developing hypothyroidism. © Georg Thieme Verlag KG Stuttgart · New York.