TG and hyperthyroidism: Theseconsiderations are particularly important when investigatingthe relationships between PFAS concentrations and thyroid dysfunction(classically categorized as hypo- and hyperthyroidism, characterizedby the under- and overproduction of thyroid hormones, respectively).The thyroid hormones, thyroxine (T4) and thyronine (T3), which maybe measured as free (unbound) and/or total (both protein-bound andunbound) concentrations, are produced by the thyroid gland in responseto pituitary thyroid-stimulating hormone (TSH) and hypothalamic thyrotropin-releasinghormone (TRH).