MBI046 - THYROXINE(T4), SERUM Detail

Thyroxine, also called T4, is synthesized in the thyroid gland using iodine and the amino acid tyrosine. It is released into the bloodstream, mostly bound to thyroid-binding globulin (TBG), with a small portion as free T4 (FT4), which is the biologically active form.

T4 is converted in tissues to triiodothyronine (T3), the more active thyroid hormone, which influences metabolic rate, protein synthesis, growth, and development.

Clinical Significance

• Low T4 levels may indicate:

  • Hypothyroidism (underactive thyroid)

  • Iodine deficiency

  • Pituitary gland disorders

• High T4 levels may indicate:

  • Hyperthyroidism (overactive thyroid)

  • Thyroid hormone overdose

  • Graves’ disease

• T4 measurement is often combined with TSH and T3 for complete thyroid assessment.

Normal Range

• Total T4 (TT4): 5–12 µg/dL

• Free T4 (FT4): 0.8–1.8 ng/dL
  (Ranges may vary slightly by laboratory)