Blood test

Low T3 level in the blood

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

What is a low T3 level in the blood called?

  • Hypotriiodothyroninemia

What is the normal T3 level in the blood?

If you need to know which are the T3 reference ranges or you require more information about the role of T3 in the blood, you can visit normal T3 level in the blood

What does a low total T3 (Triiodothyronine) level in the blood mean?

Low values of total T3 (Triiodothyronine) in the blood may be a sign of hypothyroidism where the thyroid gland fails to produce enough thyroid hormones.

T3 values in the blood are usually studied along with T4 hormone (thyroxine) and TSH (thyroid-stimulating hormone) values to give a better diagnosis.

There are two types of hypothyroidism:

  • Primary hypothyroidism: caused by a problem (hypofunction) of the thyroid gland. In this case, TSH values will be above the normal range.
  • Secondary hypothyroidism: caused by a failure of the pituitary gland. In this case TSH values, will be below the normal range.

T3 blood values are usually given in ng/ml but sometimes you can see these values in nmol/l following the International System of Units (SI). In case your values are in nmol/l you can convert them using this tool:


Hypotriiodothyroninemia or low T3 blood levels mean:

  • Marked hypotriiodothyroninemia (< 0.8 mg/dl in adults):

    T3 level in the blood is below the normal range and it is a sign of suffering from hypothyroidism, a situation that occurs when the thyroid gland does not produce enough thyroid hormones.

    T3 should be studied along with TSH (thyroid-stimulating hormone) and T4 (thyroxine) for a better diagnosis. In case it was necessary, your doctor will prescribe you the best treatment.

    T4 (thyroxine) and TSH values are more precise to diagnose primary hypothyroidism than T3 values.

    An additional test of free T3 in the blood can be asked for your doctor to get more information about the disorder.

    If your T3 level in the blood is low, you may suffer from fatigue, depression or weight gain.

Which factors can reduce the total T3 level in the blood?

Some particular health situation or drugs may reduce your T3 level in the blood:

  • Iodine deficiency
  • Malnutrition
  • Stress
  • Thyroidectomy
  • Drugs
    • Antiarrhythmic agents
      • Amiodarone
    • Antiepileptic drugs
      • Carbamazepine
      • Phenytoin
      • Phenobarbital
    • Antithyroid agent
      • Carbimazole
      • Thiamazole
      • Propylthiouracil
    • Beta blockers
      • Propranolol
    • Glucocorticoids
    • Psychotropic drugs
      • Lithium

Which diseases can reduce your total T3 level in the blood?

The following diseases can explain a total T3 level in the blood lower than normal:

What can I do to increase the total T3 level in the blood?

If the T3 (Triiodothyronine) level in the blood is low the following tips can help you:

  • Increase your iodine intake in your diet if your current intake is inadequate (iodized salt, cod, etc.). It is not usually a problem in developed countries.
  • You can take, under medical prescription, levothyroxine (a manufactured form of the thyroid hormone thyroxine T4). It is recommended to take T4 hormone instead of T3 hormone (Liothyronine) because T4 can be converted into T3 and it is an easy and effective treatment.

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

You can visit our pages about:

Which values are considered a low T3 level in the blood?

The following values are considered to be above the normal range:

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.

Marked hypotriiodothyroninemia
0.79 ng/ml0.78 ng/ml0.77 ng/ml0.76 ng/ml0.75 ng/ml0.74 ng/ml0.73 ng/ml0.72 ng/ml
0.71 ng/ml0.7 ng/ml0.69 ng/ml0.68 ng/ml0.67 ng/ml0.66 ng/ml0.65 ng/ml0.64 ng/ml
0.63 ng/ml0.62 ng/ml0.61 ng/ml0.6 ng/ml0.59 ng/ml0.58 ng/ml0.57 ng/ml0.56 ng/ml
0.55 ng/ml0.54 ng/ml0.53 ng/ml0.52 ng/ml0.51 ng/ml0.5 ng/ml0.49 ng/ml0.48 ng/ml
0.47 ng/ml0.46 ng/ml0.45 ng/ml0.44 ng/ml0.43 ng/ml0.42 ng/ml0.41 ng/ml0.4 ng/ml
0.39 ng/ml0.38 ng/ml0.37 ng/ml0.36 ng/ml0.35 ng/ml0.34 ng/ml0.33 ng/ml0.32 ng/ml
0.31 ng/ml0.3 ng/ml0.29 ng/ml0.28 ng/ml0.27 ng/ml0.26 ng/ml0.25 ng/ml0.24 ng/ml
0.23 ng/ml0.22 ng/ml0.21 ng/ml0.2 ng/ml0.19 ng/ml0.18 ng/ml0.17 ng/ml0.16 ng/ml
0.15 ng/ml0.14 ng/ml0.13 ng/ml0.12 ng/ml0.11 ng/ml0.1 ng/ml0.09 ng/ml0.08 ng/ml
0.07 ng/ml0.06 ng/ml0.05 ng/ml0.04 ng/ml0.03 ng/ml0.02 ng/ml0.01 ng/ml0 ng/ml
Medically reviewed by our Medical staff on 20/10/2020


  • Approved Guideline – Procedures for the Handling and Processing of Blood Specimens, H18-A3. 2004. Clinical and Laboratory Standards Institute.
  • 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.

Show more

Rating Overview

Share your thoughts about this content

E-mail (Optional):
Add a review