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T3 (Total Triiodothyronine)

The Total T3 test measures the bound(T3) and free forms of T3(FreeT3) levels in the blood to evaluate the thyroid functioning if it has underactive(Hypothyroidism) or overactive(Hyperthyroidism) performance.

The T3 hormone comes in two forms:

  • Bound T3, which attaches to protein
  • Free T3, which does not attach to anything
Also Known asT3, FT3, Total T3, Free T3, Triiodothyronine, Free Triiodothyronine, Total Triiodothyronine
Test Purpose1. To help evaluate thyroid gland function
2. To diagnose thyroid disease, including hyperthyroidism, and determine the cause
3. To monitor effectiveness of treatment of a thyroid disorder
Test PreparationsNo Special Preparation Required
Test ComponentsTotal Triiodothyronine (T3)
Free Triiodothyronine (FT3)
Specimen3 ML (1.5 ML Min.) Serum From 1 SST Tube
Stability Room2 Hrs
Stability Refrigerated1 Week
Stability Frozen4 Weeks
MethodChemiluminescent Immunoassay
Download ReportDownload Report

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Difference between T3 and FT3

T3 has 2 forms: bound and free. Bound T3 is attached to a protein and free T3 is not attached to anything. The free T-3 test measures only the amount of free T3. The total T3 test measures both free and bound T3 in your blood.



The thyroid is a small butterfly-shaped gland present in the neck region and is responsible for various functions of the body, including metabolism and growth. Triiodothyronine (T3) is one of the hormones produced by the thyroid gland. This test is done to assess thyroid function and measures the blood level of the T3 hormone. T3 is four times more powerful than T4. Being secreted by the thyroid gland, T3 and T4 play an important role in the growth of the human body.

Free T3:

Free Triiodothyronine test measures the amount of T3 in the blood. Blood levels of T3 are higher or lower because of inadequate or uncontrolled production of the hormone by the thyroid gland because of thyroid dysfunction or pituitary dysfunction. Abnormal levels of T3 in the blood are related tp hyperthyroidism, hypothyroidism, and slow metabolism.

Why Get Tested:

  • Triiodothyronine is given to detect thyroid dysfunction.
  • It helps diagnose hyperthyroidism, a condition in which the thyroid produces excess hormones.
  • This test helps detect infertility in women.
  • This test is not affected by protein level and is therefore more accurate.
  • An overactive thyroid (overactive thyroid gland function), underactive thyroid (low thyroid gland function), and hypopituitarism (underactive pituitary gland) are some of the disorders that affect the thyroid gland.

Normal Values

Source 1:

  1. Triiodothyronine (T3): 80-180 ng/dl
  2. Free T3: 230-619 pg/dl

Source 2 (T3):

  • 0-5 days: 73-288 ng/dL
  • 6 days-2 months: 80-275 ng/dL
  • 3-11 months: 86-265 ng/dL
  • 1-5 years: 92-248 ng/dL
  • 6-10 years: 93-231 ng/dL
  • 11-19 years: 91-218 ng/dL
  • Adult (> or =20 years): 80-200 ng/dL

Source 2 (F T3):

  • Cord blood (>37 weeks ) = 15 to 391 pg/dL
  • Child and adult = 260 to 480 pg/dL  (4.0 to 7.4 pmol/L)
  • Pregnancy
    • First trimester = 211 to 383 pg/dL
    • Second and third trimester = 196 to 338 pg/dL

TSHTotal and Free T4Total and Free T3MOST LIKELY DIAGNOSIS
NormalNormalNormalNormal thyroid function (e.g., “euthyroid”)
Normal or decreasedNormal or decreasedDecreasedNormal adjustment in thyroid function due to illness (nonthyroidal illness or sick euthyroid syndrome)
IncreasedNormalNormalSubclinical hypothyroidism1; in a person with hypothyroidism on treatment, not enough thyroid hormone is being given
IncreasedDecreasedNormal of decreasedHypothyroidism resulting from a problem with the thyroid gland itself (primary hypothyroidism)
Normal or increasedIncreasedIncreasedHyperthyroidism resulting from a problem with the pituitary gland signals (central hyperthyroidism) or from a problem with the thyroid hormone receptor (thyroid hormone resistance)
DecreasedNormalNormalSubclinical hyperthyroidism2; in a person with hypothyroidism, too much thyroid hormone is being given
DecreasedNormalIncreasedHyperthyroidism resulting from the thyroid gland making too much active thyroid hormone T3 (uncommon, also known as T3 toxicosis)
DecreasedIncreasedIncreasedHyperthyroidism resulting from the gland making too much thyroid hormones (primary hyperthyroidism)
DecreasedDecreasedDecreasedHypothyroidism resulting from a problem with the hypothalamus or pituitary signals that govern the thyroid gland (central hypothyroidism)

Increased Level Of T3:

  1. primary hyperthyroidism like :
    1. grave’s disease.
    2. Toxic thyroid adenoma.
  2. Acute thyroiditis. In the early stages, the thyroid produces more T3.
  3. Ectopic thyroid tissue e.g. Struma ovarii.
  4. Increased Thyroid binding globulin, seen in pregnancy, Hepatitis, and congenital hyperproteinemia.

Decreased Level Of T3:

  1. Hypothyroidism is seen in :
    1. Cretinism.
    2. Surgical ablation.
    3. Myxedema.
  2. Hypothalamic failure.
  3. Nephrotic syndrome.
  4. Iodine insufficiency.
  5. Pituitary insufficiency.
  6. Renal failure.
  7. Cirrhosis.
  8. advanced cancer.
  9. hepatic diseases.

Increased Level of Free T3 :

  1. T3 toxicosis.
  2. Hyperthyroidism.
  3. Peripheral resistance syndrome.

Decreased Level of Free T3 :

  1. Hypothyroidism.
  2. Pregnancy in the third trimester.

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