Triiodothyronine (T3) Total

Triiodothyronine (T3) Total

Triiodothyronine (T3) is one of the two primary hormones produced by the thyroid gland, containing three iodine atoms in its structure. It has greater activity compared to thyroxine (T4) but circulates in the blood in much smaller quantities. A portion of the hormone is synthesized “from scratch,” while the rest is formed during the breakdown of thyroxine.

Triiodothyronine participates in regulating metabolic processes: it increases protein production, contributes to the breakdown of fats and carbohydrates with the release of significant amounts of energy. It also enhances cells’ oxygen consumption and aids in the more efficient absorption of vitamins and trace elements in the intestines. This compound is mostly found in the blood bound to carrier proteins. Less than 1% is present in the free form, i.e., in a biologically active form.

Synonyms: Total Triiodothyronine, TT3.

Indications for analysis:
This test is directed when there is suspicion of thyroid gland problems, which may manifest as symptoms such as:

  1. Increased or decreased heart rate.
  2. Fluctuations in blood pressure.
  3. Insomnia or drowsiness.
  4. Excitability or nervousness.
  5. Increase or decrease in weight with corresponding increase or decrease in appetite.
  6. Menstrual cycle disturbances.
  7. Swellings.
  8. Dryness of the skin and hair, etc.

The test is also necessary when discovering enlargement or nodules in the thyroid gland, and when there are changes in thyroid-stimulating hormone (TSH) levels, and during treatment (to monitor its effectiveness).

Test description:
The hormone analysis method uses a radioimmunoassay (RIA) test to evaluate hormone levels. This test requires the withdrawal of a blood sample from the patient’s vein.

Preparation for the Test:

The test results will be reliable if the patient takes sufficient care in preparation:

  1. Refrain from taking thyroid hormones and steroids 48 hours before the test (only with the permission of the treating physician).
  2. Avoid stress and physical exertion 24 hours before sample collection.
  3. Exclude alcohol and fatty foods consumption 24 hours before.
  4. Abstain from eating and drinking, except for plain water, and refrain from smoking 3-4 hours before the procedure.

Normal Concentration:

Measurement units: Nanomoles per liter (nMol/L).

Reference Values within the Table:

Measurement units: Nanomoles per liter (nMol/L).

Patient’s Age Total T3 Level (Nanomoles per liter)
Less than 4 months 1.23 – 4.22
4 months – 1 year 1.32 – 4.07
1 year – 7 years 1.42 – 3.80
7 – 12 years 1.43 – 3.55
12 – 20 years 1.40 – 3.34
Greater than 20 years 1.2 – 3.1

Reference values: Total T3 level depends on age.

Analytical Result:

Excess Total T3:

  • Various types of hyperthyroidism and thyroid hormone excess.
  • Graves’ disease.
  • Postpartum thyroid dysfunction.
  • Thyroid gland tumor.
  • Tissue resistance to thyroid hormones syndrome.
  • Pendred syndrome (congenital disorder).
  • Elevated concentration may also occur due to the intake of birth control pills containing estrogen, certain antibiotics, and cancer drugs. Additionally, it can be higher than normal during pregnancy or in cases of severe liver diseases.

Deficiency Total T3:

  • Thyroid gland inflammation in acute or subacute forms (thyroiditis).
  • Hypothyroidism (insufficient thyroid hormone function).
  • Starvation (loss of appetite).
  • Severe and prolonged iodine deficiency.
  • Radioactive iodine therapy.
  • Kidney or liver failure.
  • Recent surgeries or injuries.
  • Hepatic salt wasting.
  • Postpartum syndrome due to containing doses of thyroid hormone.
  • Reduction in T3 also occurs due to the intake of medications such as antiarrhythmics, anabolic steroids, some anticonvulsants, antihypertensives, androgens, hormones, aspirin derivatives, diuretics, and some other medications.

Additional Examination When Outside the Normal Range:

If the total T3 level is elevated, the patient should undergo blood analysis to evaluate hormone and antibody levels, which are markers of thyroid function: Free T3, TSH, Free and Total T4, and antibodies to thyroglobulin and thyroperoxidase. Additionally, thyroid ultrasound examination and medical consultation with an endocrinologist are recommended.