Men: 4 - 12 µg/dl
Women: 4 - 12 µg/dl
Children from 11 to 18 years old: 6 - 13 µg/dl
Children from 6 to 10 years old: 6 - 14 µg/dl
Children from 1 to 5 years old: 6 - 14.5 µg/dl
Newborns: 5 - 18.5 µg/dl
In the International System of Units (SI), T4 in the blood is measured in nmol/L. The normal T4 levels in the blood in the SI are:
Men: 51.48 - 154.46 nmol/L
Women: 51.48 - 154.46 nmol/L
Children from 11 to 18 years old: 77.23 - 167.33 nmol/L
Children from 6 to 10 years old: 77.23 - 180.20 nmol/L
Children from 1 to 5 years old: 77.23 - 186.64 nmol/L
Newborns: 77.23 - 238.13 nmol/L
Each laboratory must establish its own normal ranges for the total T4 (Thyroxine) 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 T4 (Thyroxine) is measured instead of total T4, the normal levels in adults are from 0.8 to 2 ng/ml.
Pregnant women have normal values above the ranges before.
T4 hormone (thyroxine) is produced by the thyroid gland, placed near the neck, along with the T3 hormone (Triiodothyronine). Both hormone production is primarily regulated by the thyroid-stimulating hormone (TSH) that is released from the pituitary gland.
T4 (thyroxine) main roles in the body are:
T4 (thyroxine) plays a crucial role in metabolism. Thyroxine regulates how sugar is converted into energy necessary for the body, avoiding the fat storage. If the body needs more energy, there is an increase in T4 production. That is the reason why people with a low T4 level in the blood tend to gain weight and, on the other hand, people with a high T4 level in the blood are more prone to lose weight.
T4 hormone is the thyroid hormone present in higher amounts in the body. It can be converted into T3 hormone, which is four times more active.
T4 (thyroxine) hormone level in the blood is used to detect thyroid disorders. The test should be performed along with T3 (Triiodothyronine) level and TSH (thyroid-stimulating hormone) level to have a complete study of the thyroid status.
T4 hormone can be found in the blood in a free way or bound to other proteins (such as albumin, TBPA - Thyroxine-binding prealbumin or TBP - Thyroxine-binding globulin). In a blood test it is more common to measure the total T4 hormone because only a 1% of the T4 hormone in the blood is free.
High values of T4 in the blood may be a sign of hyperthyroidism. Low values of T4 in the blood may be a sign of hypothyroidism.
It is common to screen newborns with a T4 blood test to detect congenital iodine deficiency syndrome, a disease that untreated results in impairment of physical and mental development.
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The following values are considered to be normal values:
IMPORTANT: These levels are expressed in µg/dl. 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.
T4 | |||||||
|---|---|---|---|---|---|---|---|
| Normality | |||||||
| 4 µg/dl | 4.1 µg/dl | 4.2 µg/dl | 4.3 µg/dl | 4.4 µg/dl | 4.5 µg/dl | 4.6 µg/dl | 4.7 µg/dl |
| 4.8 µg/dl | 4.9 µg/dl | 5 µg/dl | 5.1 µg/dl | 5.2 µg/dl | 5.3 µg/dl | 5.4 µg/dl | 5.5 µg/dl |
| 5.6 µg/dl | 5.7 µg/dl | 5.8 µg/dl | 5.9 µg/dl | 6 µg/dl | 6.1 µg/dl | 6.2 µg/dl | 6.3 µg/dl |
| 6.4 µg/dl | 6.5 µg/dl | 6.6 µg/dl | 6.7 µg/dl | 6.8 µg/dl | 6.9 µg/dl | 7 µg/dl | 7.1 µg/dl |
| 7.2 µg/dl | 7.3 µg/dl | 7.4 µg/dl | 7.5 µg/dl | 7.6 µg/dl | 7.7 µg/dl | 7.8 µg/dl | 7.9 µg/dl |
| 8 µg/dl | 8.1 µg/dl | 8.2 µg/dl | 8.3 µg/dl | 8.4 µg/dl | 8.5 µg/dl | 8.6 µg/dl | 8.7 µg/dl |
| 8.8 µg/dl | 8.9 µg/dl | 9 µg/dl | 9.1 µg/dl | 9.2 µg/dl | 9.3 µg/dl | 9.4 µg/dl | 9.5 µg/dl |
| 9.6 µg/dl | 9.7 µg/dl | 9.8 µg/dl | 9.9 µg/dl | 10 µg/dl | 10.1 µg/dl | 10.2 µg/dl | 10.3 µg/dl |
| 10.4 µg/dl | 10.5 µg/dl | 10.6 µg/dl | 10.7 µg/dl | 10.8 µg/dl | 10.9 µg/dl | 11 µg/dl | 11.1 µg/dl |
| 11.2 µg/dl | 11.3 µg/dl | 11.4 µg/dl | 11.5 µg/dl | 11.6 µg/dl | 11.7 µg/dl | 11.8 µg/dl | 11.9 µg/dl |
| 12 µg/dl | |||||||
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