was ist ft3 — which blood markers matter?

FT3 (free triiodothyronine) is the active thyroid hormone that regulates metabolism. Key blood markers for thyroid function include: TSH (thyroid-stimulating hormone) as the primary screening test, fT4 (free thyroxine) as the prohormone, and fT3 itself. Additional markers such as thyroid antibodies (TPO-Ab, Tg-Ab, TSH-receptor-Ab) are relevant when autoimmune thyroid disease is suspected. An isolated low fT3 with normal TSH and fT4 may indicate euthyroid sick syndrome (non-thyroidal illness) rather than primary thyroid dysfunction. Interpretation must be done in clinical context. Note: The provided context contains no specific information on fT3 or thyroid markers; this answer is based on general medical knowledge.