Which antibody is most likely positive in autoimmune hypothyroidism?

• A. Thyroid peroxidase antibodies
• B. Anti-dsDNA antibodies
• C. Anti-La antibodies
• D. Anti-Scl-70 antibodies

Answer: (A)

Autoimmune hypothyroidism is most often due to Hashimoto thyroiditis, where the immune system targets thyroid tissue. The most common serologic finding is antibodies against thyroid enzymes, especially thyroid peroxidase (TPO). These anti-TPO antibodies reflect autoimmunity against the thyroid and are frequently present in Hashimoto’s, sometimes along with anti-thyroglobulin antibodies.

The other antibodies listed are associated with different autoimmune diseases: anti-dsDNA with lupus, anti-La with Sjögren syndrome (and sometimes lupus), and anti-Scl-70 with systemic sclerosis. They are not typical markers of autoimmune thyroiditis. Therefore, anti-thyroid peroxidase antibodies are the best indicator of autoimmune hypothyroidism.