Thyroxine, Free (FT4)

Analyte [material]

Thyroxine, free (FT^₄) [S/P]

Reference range, target level, or decision threshold

10-25 pmol/L (8-20 ng/L)

[pmol/L] × 0.8 = [ng/L] (depending on the method)CW !

Interpretation of results

↑ Hyperthyroidism (adult and neonatal Graves disease), thyroid hormone resistance, thyroxine replacement therapy, drugs (amiodarone, heparin), thyroid-stimulatig hormone (TSH)-secreting pituitary adenoma, thyroiditis (postviral, postpartum), excess iodine intake, pregnancy-related conditions (hyperemesis gravidarum, hydatidiform mole), congenital hyperthyroidism

↓ Hypothyroidism, autoimmune thyroiditis (Hashimoto, atrophic), after radioiodine therapy, after thyroidectomy, drugs (amiodarone, lithium, tyrosine kinase inhibitors), Riedel thyroiditis, thyroid infiltration (tumor, amyloid), TSH deficiency

Do not use free T4 or triiodothyronine (T3) to screen for hypothyroidism or to monitor and adjust levothyroxine (L-T4) dose in patients with known primary hypothyroidism, unless the patient has suspected or known pituitary or hypothalamic disease.