Decreased T4

A reduced serum thyroxine (T4) concentration below the assay reference range (usually free T4 0.8–1.8 ng/dL or 10.3–24.5 pmol/L).

Causes

• Primary hypothyroidism

  • Autoimmune Hashimoto's disease

  • Thyroid surgery

  • Radiation therapy

  • Congenital hypothyroidism

• Central hypothyroidism

  • Pituitary tumor

  • Pituitary hemorrhage

• Non-thyroidal illness

• Lithium

• Iodine deficiency