source: Medscape

year: 2021

authors: Karen Tsai, Trevor E. Angell, Melissa G. Lechner

A healthy 52-year-old woman has had persistent palpitations recently. Serum TSH is < 0.02 mIU/mL (reference, 0.3-4.7 mIU/mL), free T4 is 5.70 ng/dL (reference, 0.8-1.7 ng/dL), and free triiodothyronine (T3) is 1920 pg/dL (reference, 222-383 pg/nL). She has fine bilateral hand tremors and sinus tachycardia. How do we work up this new diagnosis of thyrotoxicosis?

This is one of the most common consults we receive. Thyroid antibodies may be helpful in teasing apart the differential diagnosis of thyrotoxicosis.

TSH receptor antibodies (TRAb) target the TSH receptor and may have an inhibitory, neutral, or stimulating effect. The thyrotropin binding inhibitory immunoglobulin (TBII) test measures antibodies that inhibit TSH binding to its receptor. Stimulating TRAbs, known as thyroid-stimulating immunoglobulins (TSIs), are associated with Graves’ disease; they stimulate the TSH receptor, leading to increased production and release of thyroid hormone. Though the names may vary in commercial labs, positive TBII, TRAb, or TSI titers can all be used to diagnose Graves’ disease.

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