Prevalence of Antithyroid Antibodies in Histologically Proven Autoimmune Thyroid Diseases and Correlation with Thyroid Dysfunction in South India

Objective: The clinical diagnosis of autoimmune thyroid diseases (AITD) is usually confirmed by detection of various antibodies in the patient’s blood or by histopathological evaluation. In this study, we evaluated the prevalence of serum antibodies in histopathologically proven AITD and assessed the correlation between antibodies and thyroid dysfunction. Methods: 100 consecutive patients with a histological diagnosis of AITD were included in the study and underwent detailed clinical examination and testing for thyroid function, thyroid antibodies, thyroid ultrasound scan, and thyroid gland fine-needle aspiration cytology. Results: Thyroid peroxidase antibodies (TPO Ab) tested positive in 89% of patients and negative in 11%. Antithyroglobulin antibody (ATG Ab) estimation was positive in 64 % of patients and negative in 36%. By thyroid function testing and serum antibody evaluation, of the 89 TPO-positive patients, 60.7% were hypothyroid, 6.7% hyperthyroid, and 32.6% euthyroid. Among euthyroid patients, 90% were TPO-Ab negative. In 64 ATG Ab-positive patients, 53.1% patients were hypothyroid, 4.7% hyperthyroid, and 42.2% euthyroid. But in the 36 ATG Ab-negative patients, 58.3% were hypothyroid. At the time of the first clinic visit, 55% of patients were hypothyroid, 6% hyperthyroid, and 39% euthyroid. Conclusion: In our study, TPO Ab was more sensitive than ATG Ab in predicting hypothyroidism. Similarly, TPO Ab was more sensitive than ATG Ab in autoimmune thyroiditis (98.1% vs 61.8%, p value < 0.005). Hypothyroidism was the most frequent thyroid dysfunction in patients with positive TPO and ATG antibodies . The absence of TPO usually is associated with no thyroid dysfunction, but the same cannot be said of ATG.