In Hashimoto thyroiditis, the autoantibody found in over 90 percent of patients and directed against the enzyme involved in thyroid hormone synthesis is:

• A Anti-thyroid peroxidase (anti-microsomal) antibody ✓
• B Anti-thyroid stimulating hormone receptor antibody
• C Anti-sodium-iodide symporter antibody
• D Anti-thyreoglobulin antibody alone

Explanation

Anti-thyroid peroxidase (previously called anti-microsomal) antibodies are present in more than 90 percent of Hashimoto patients and target the enzyme that iodinates thyroglobulin. Anti-TSH receptor antibodies define Graves disease, making option B the classic trap. Anti-thyroglobulin antibodies occur in about 60 percent of cases and add little diagnostic weight alone, so option D understates the single best marker.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.