was ist ft3 und ft4 — what are common causes?

FT3 (free triiodothyronine) and FT4 (free thyroxine) are the unbound, biologically active fractions of thyroid hormones in the blood. They regulate metabolism, heart rate, body temperature, and organ function. Common causes of abnormal levels: Elevated FT3/FT4 (hyperthyroidism) often result from Graves' disease, toxic nodular goiter, thyroiditis (e.g., De Quervain, early Hashimoto), or excessive levothyroxine intake. Low FT3/FT4 (hypothyroidism) are typically caused by chronic autoimmune thyroiditis (Hashimoto), iodine deficiency, thyroidectomy, or insufficient thyroid hormone medication. Pituitary disorders (secondary hypothyroidism) and non-thyroidal illness (low T3 syndrome) can also alter levels. Important: A single measurement does not diagnose disease; clinical context and additional labs (TSH, antibodies) are needed. Note: MyBody-X tests do not measure thyroid hormones; these require a blood draw. Always consult an endocrinologist for interpretation and treatment.