Hyperthyroidism

• Similar to FT4, elevated FT3 is often seen in conditions such as Graves’ disease.

De-differentiation or Over-conversion

• In some thyroid disorders, increased conversion of T4 to T3 can drive high FT3 levels even when T4 remains normal.

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Hypothyroidism or “Sick Euthyroid” Syndrome

• Critical illness or non-thyroidal illness can lower FT3 despite normal T4.

Underactive Thyroid

• Autoimmune thyroid destruction (Hashimoto’s thyroiditis) or iodine deficiency may result in low FT3.

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Neonates & Children

• FT3 is important in regulating metabolic rate and brain development.
• Its levels change as the endocrine system matures.

Adults/Elderly

• Altered FT3 — especially in the elderly — might signal thyroid dysfunction or be part of a broader systemic illness.

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Thyroid Function

• Common Thyroxine (T4), Free Thyroxine (FT4), Free Triiodothyronine (FT3):
  These markers measure the overall thyroid hormone production and the bioavailable (active) fractions. While Common T4 reflects total hormone levels (both bound and free), FT4 and FT3 specifically indicate the unbound, active hormones that drive metabolic processes.
  
  
• Thyrotropic Hormone (TSH):
  This pituitary hormone regulates thyroid hormone synthesis through a negative feedback mechanism. Elevated or suppressed TSH levels provide insight into thyroid function and help direct further evaluation of thyroid disorders.
  
  
• Thyroxine Binding Globulin (TBG):
  TBG is the main protein binding thyroid hormones in the blood. It influences the proportion of hormone that remains free versus bound, affecting the interpretation of Common T4 compared to FT4 and FT3 levels.
  
  
• thyreoglobulin;calcitonin; tumerous marker thyreoglobulin:
  These markers focus on thyroid tissue activity and neoplastic surveillance.
  
  
  
  • thyreoglobulin reflects the functional activity of thyroid follicular cells.
  • When used as a tumour marker (tumerous marker thyreoglobulin), it helps monitor for residual or recurrent differentiated thyroid cancer following treatment.
  • calcitonin, secreted by the thyroid’s C cells, is particularly valuable in detecting medullary thyroid carcinoma.

Together, these markers offer a comprehensive view of thyroid gland function, regulation, and tissue integrity, integrating hormonal activity with diagnostic tools for thyroid cancer surveillance.

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