Objective: To evaluate the immunoglobulin G subclasses of anti-TPO and antibody avidity in patients with subclinical hypothyroidism (sH), overt hypothyroidism (H) and a control group (C). Methods: According to the TSH, fT4 and anti-TPO antibody levels, appraised by immunometric assays, 95 female patients were divided into three groups (sH, H and C). IgG subclass levels and avidity were measured by a homemade ELISA. Results were analyzed by nonparametric tests and Spearman’s rank correlation. Results: The predominant IgG subclasses detected in both case groups were IgG1 and IgG4 with a significantly higher level of IgG4 in the sH group. Consequently, the IgG1/IgG4 ratio was significantly lower in sH patients. Conclusion: The higher levels of IgG4 anti-TPO reduced significantly the IgG1/IgG4 ratio in sH patients. These results permit to envisage that increasing this ratio could be useful as a positive predictive factor for the development of overt disease in such patients.

Keywords:
Subclinical hypothyroidism, Anti-TPO, Anti-TPO avidity, Anti-TPO subclasses
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