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Normal T3 level in the blood

Blood test
Normal T3 level in the blood
Last update: 20/10/2020

What is the normal T3 (Triiodothyronine) level in the blood?

Men: 0.8 - 2 ng/ml
Women: 0.8 - 2 ng/ml
Children from 13 to 18 years old: 0.65 - 1.6 ng/ml
Children from 7 to 12 years old: 0.70 - 1.9 ng/ml
Children from 1 to 7 years old: 0.75 - 1.8 ng/ml
Children up to 1 year old: 0.8 - 1.8 ng/ml
Newborns: 0.3 - 1.8 ng/ml

In the International System of Units (SI), T3 in the blood is measured in nmol/l. The normal T3 levels in the blood in the SI are:

Men: 1.22 - 3.07 nmol/L
Women: 1.22 - 3.07 nmol/L
Children from 13 to 18 years old: 1 - 2.45 nmol/L
Children from 7 to 12 years old: 1.07 - 2.91 nmol/L
Children from 1 to 7 years old: 1.15 - 2.75 nmol/L
Children up to 1 year old: 1.22 - 2.75 nmol/L
Newborns: 0.46 - 2.75 nmol/L

Why normal levels can differ across different labs?

Each laboratory must establish its own normal ranges for the total T3 (Triiodothyronine) in the blood. These ranges depend on the makeup of the local population, the technologies used and the accuracy of the measurement. There may be also slight differences in the normal levels, according to age, gender, race or ethnic origin, geographic region, diet, type of sample and other relevant status.

Your doctor will study the results along with your medical record, screenings, physical condition, symptoms and any other relevant information about your situation.

If free T3 is measured instead of total T3, the normal levels in adults are from 2.3 to 4.2 pg/ml.

What is the role of T3 (Triiodothyronine)?

T3 hormone (Triiodothyronine) is produced by the thyroid gland along with the T4 hormone (thyroxine). Both hormones are primarily regulated by the thyroid-stimulating hormone (TSH) that is released from the pituitary gland. Most part of T3 hormone contains iodide ions.

T3 presence in the blood is less than T4 hormone, but its effect is 6 to 8 times more potent than those of T4 hormone are. That can explain why T4 hormone can be converted into T3. Most of this conversion happens, if it is necessary, in the liver or the kidneys. Only 20% of T3 hormone present in the body is produced by the thyroid gland. The other 80% is created by conversion of T4 into T3.

T3 hormone plays a crucial role in the body:

  • Influence on metabolism (appetite regulation, insulin secretion, etc.)
  • Regulation of growth and development.
  • Control the heart rate.
  • Regulation of body temperature.
  • Influence on gastrointestinal motility.

What is a total T3 (Triiodothyronine) blood test used for?

T3 (Triiodothyronine) hormone level in the blood is used to detect thyroid disorders. This test should be performed along with T4 hormone (thyroxine) and TSH (thyroid-stimulating hormone) for a better understanding of the thyroid functionality.

T3 hormone can be found in the blood in a free way or bound to other proteins (such as albumin or TBG - Thyroxine-binding globulin). In a blood test it is more common to measure the total T3 hormone because only a 3% of the T3 hormone in the blood is free.

High values of T3 in the blood may be a sign of hyperthyroidism, even if the T4 values are in the normal range. Low values of T3 may be a sign of hypothyroidism.

The study of T3 along with TSH is important to know if the thyroid disorder is primary (due to a thyroid gland problem) or secondary (due to a malfunction of the hypothalamus or the pituitary gland).

Where can I find more information about T3 (Triiodothyronine) level in the blood?

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Which values are considered a normal T3 (Triiodothyronine) level in the blood?

The following values are considered to be normal values:

IMPORTANT: These levels are expressed in ng/ml. They are an example of a healthy man of about 45 years old with no known disease and not taking any medication. The ranges can be different depending on the laboratory or on your personal circumstances.

0.8 ng/ml0.9 ng/ml1 ng/ml1.1 ng/ml1.2 ng/ml1.3 ng/ml1.4 ng/ml1.5 ng/ml
1.6 ng/ml1.7 ng/ml1.8 ng/ml1.9 ng/ml2 ng/ml   
Medically reviewed by our Medical staff on 20/10/2020


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  • HHS Publication, 6th ed., June 2020. Biosafety in Microbiological and Biomedical Laboratories. Available on:
  • Concise Book of Medical Laboratory Technology: Methods and Interpretations. 2nd Edition. 2015. Ramnik Sood. ISBN: 978-93-5152-333-8. Pag. 783.
  • Tietz. Fundamentals of Clinical Chemistry. Carl A. Burtis, Edward R. Ashwood, David E. Bruns, Barbara G. Sawyer. WB Saunders Company, 2008. Pag 766. ISBN: 978-0-7216-3865-2.
  • Laboratory tests and diagnostic procedures with nursing diagnoses (8th ed), Jane Vincent Corbett, Angela Denise Banks, ISBN: 978-0-13-237332-6, Pag. 400.

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