Thyroxine (T4) Total

Thyroxine (T4) Total

Thyroxine (T4) is one of the key hormones produced by the thyroid gland, playing a role in regulating metabolic processes in the body. It controls oxygen consumption by cells, affects temperature regulation and heart function, and ensures proper growth (in children) and nervous system function.

The compound circulates in the blood in two forms: free (biologically active) and protein-bound. Total T4 serves as a composite index of these two values. This index is a supplementary measure for evaluating thyroid function, heavily reliant on the amount of transport proteins in the body and does not accurately reflect hormone activity.

Synonyms: Total thyroxine, Total T4, Total thyroxine, Thyroxine, Total T4.

Indications for Analysis:
Total T4 analysis allows detection of thyroid function abnormalities in childhood or adulthood, assesses disease stage, aids in treatment selection, and evaluates its effectiveness. For routine monitoring, regular analysis every 3-4 months is required. It is also requested when problems arise due to thyroid hormone deficiency or excess, such as female infertility.

Analysis Description:

The analysis for diagnosis uses the radioimmunoassay technique. The patient must provide a sample of venous blood, from which serum is extracted.

Preparation for Analysis:

Two days before the diagnosis, the patient must stop taking hormonal medications (especially those containing steroids or thyroid hormones), only allowed after consulting a physician. Alcohol, fatty, and fried foods should be avoided for a day before the procedure, as well as refraining from physical and emotional activity. Eating and drinking, except for plain water, and smoking should be avoided 3 hours before the procedure.

Normal Concentration:
Measurement Units: (nanomoles per liter)

Age GroupNormal Range for Total T4 (nanomoles per liter)
Less than 4 months69.6 – 219
4 months – 1 year73.0 – 206
1 year – 7 years76.6 – 189
7 – 12 years77.1 – 178
12 – 20 years76.1 – 170
Over 20 years66 – 181
Measurement Units: (nanomoles per liter)

Analytical Results:

  • Increase in T4:
  • Due to the effects of heparin, amiodarone, aspirin, blood pressure medications, and certain diuretics.
  • May indicate thyroid disorders or conditions such as diffuse toxic goiter and others.
  • Decrease in T4:
  • Could result from decreased thyroid function or other conditions such as Hashimoto’s thyroiditis and thyroiditis.
    Additional Tests:
  • Consultation with an endocrinologist and thyroid surgeon is preferred.
  • Testing for T3 and TSH levels should be performed.
  • Ultrasound examination of the thyroid gland is recommended.
  • Vladimir Vladimirovich Dolgov, Vadim Vladimirovich Menshikov. Clinical Laboratory Diagnostics. National Guidelines. In 2 volumes. GEOTAR-Media, 2013.