A 28-year-old female presents with heat intolerance, weight loss, fine hand tremor, and diffuse painless goiter. Laboratory tests show TSH < 0.01 mIU/L and elevated free T4. Which laboratory finding confirms Graves' disease?

Answer and explanation

Correct answer: D. Thyroid-stimulating immunoglobulin (TSI / TRAb)

  1. Step 1: Graves' disease is an autoimmune condition caused by autoantibodies directed against the TSH receptor on thyroid follicular cells.
  2. Step 2: Thyroid-stimulating immunoglobulins (TSI or TSH-receptor antibodies, TRAb) stimulate thyroid hormone production autonomously.
  3. Step 3: Detecting elevated TSI/TRAb confirms Graves' disease over other causes of hyperthyroidism.
Answer
Thyroid-stimulating immunoglobulin (TSI / TRAb).
Why not the others: 'Anti-thyroglobulin antibodies' are non-specific and found in Hashimoto thyroiditis; 'Anti-thyroperoxidase (anti-TPO) antibodies' are characteristic of Hashimoto thyroiditis and autoimmune hypothyroidism; 'Elevated serum calcitonin' is the tumor marker for medullary thyroid carcinoma.

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