Description:
T3 and T4 hormones are by the thyroid gland. Thyroid gland is a small butterfly-shaped organ that lies flat across your windpipe. T3 and T4 control the rate at which the body uses energy. When blood levels of thyroid hormones decline, the hypothalamus releases thyrotropin releasing hormone, which stimulates the pituitary to produce thyroid-stimulating hormone (TSH). TSH then stimulates the thyroid gland to produce hormones. Most of the thyroid hormone produced is T4. This hormone is relatively inactive, but it is converted into the much more active T3 in the liver.
If the thyroid gland produces a lot of T4 and T3, then the patient may have symptoms associated with hyperthyroidism, such as nervousness, tremors of the hands, weight loss, insomnia, and puffiness around dry, irritated eyes.
If the thyroid gland produces insufficient hormones, then the patient may have symptoms associated with hypothyroidism and a slowed metabolism, such as weight gain, dry skin, fatigue, and constipation.
About 99.7% of the T3 found in the blood is attached to a protein and the rest is free.
Its concentration is measured by means of analysis of a blood sample drawn from the vein in the arm.
Purpose of the test
To meassure the level of the T3 hormone in blood in order to detect problems of hyperthyroidism or hypothyroidism.
A T3 test helps to see whether the thyroid is functioning properly. Mainly to help diagnose hyperthyroidism. The T3 test is usually following an abnormal TSH and T4 test. T3 testing may be ordered along with thyroid antibodies to help diagnose Graves' disease, an autoimmune disorder that is the most common cause of hyperthyroidism.
A T3 test may be ordered at intervals to monitor a known thyroid condition and to help monitor the effectiveness of treatment for hyperthyroidism.
Reference range values
2.77 - 6.47pmol
Abnormal findings
If after a TSH test result high and a T4 test result normal, a T3 test result is normal, it can indicate a mild form of hypothyroidism.
If after a TSH test result high and a T4 test result low, a T3 test result is normal or low, it can indicate hypothyroidism.
If after a TSH test result low and a T4 test result normal, a T3 test result is normal, it can indicate a mild form of hyperthyroidism.
If after a TSH test result low and a T4 test result normal or high, a T3 test result is normal or high, it can indicate hyperthyroidism.
If after a TSH test result low and a T4 test result normal or low, a T3 test result is normal or low, it can indicate a nonthyroidal illness, for example a rare pituitary hypothyroidism.