Triiodothyronine, Free (FT3)

Analyte [material]

Triiodothyronine, free (FT₃) [S/P]

Reference range, target level, or decision threshold

2.25-6 pmol/L (1.5-4 ng/L) (depending on the method)CW !

[pmol/L] × 0.67 = [ng/L]

Interpretation of results

↑ Hyperthyroidism (adult and neonatal Graves disease), toxic multinodular goiter, toxic adenoma, thyroiditis (postviral, postpartum), drugs (amiodarone, heparin), excess iodine intake, excess thyroxine ingestion, pregnancy-related conditions (hyperemesis gravidarum, hydatidiform mole), congenital hyperthyroidism, thyroid hormone resistance, nonthyroidal illness, thyroid-stimulating hormone (TSH)-secreting adenoma

↓ Hypothyroidism, isolated TSH deficiency, autoimmune thyroiditis (Hashimoto, atrophic), after radioiodine therapy, after thyroidectomy, treatment with certain drugs (amiodarone, lithium, thyroid kinase inhibitors, antithyroid drugs), iodine deficiency or excess, neck irradiation, Riedel thyroiditis, thyroid infiltration (tumor, amyloid), congenital hypothyroidism

Do not use free thyroxine (FT4) or FT3 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.