A 41-year-old woman has been stable on the same dose of l-thyroxine (0.1 mg) for years, but her thyroid-stimulating hormone recently rose significantly. It turns out she has been donating plasma twice a week for the past five months. Could this be increasing her thyroid replacement needs?
—Kevin Jessen, MD, Fond du Lac, Wis.

Frequent plasma donation could certainly be increasing your patient’s thyroxine requirements. Depending on her weight, your patient is donating up to 800 mL of plasma twice a week, resulting in a total of 32 L of plasma donated over the past five months. Thyroxine is protein-bound and will be removed with the plasma. As a matter of fact, plasmapheresis has been used to treat thyrotoxicosis in cases of thyroxine ingestion and in the perioperative management of patients with Graves’ disease and contraindications to antithyroid medications.
—Susan Kashaf, MD, MPH (110-16)

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