The T3 test is requested by your doctor after a change in TSH or T4 hormone results or when the person develops signs and symptoms of hyperthyroidism, such as nervousness, weight loss, irritability and nausea, for example.
The hormone TSH is responsible for stimulating the production of T4, mainly, which is metabolized in the liver to give birth to its most active form, T3.Although most of T3 comes from T4, the thyroid also produces this hormone, but in smaller amounts.
- You don’t need to be fasting to do the test.
- However.
- Some medications may interfere with the test result.
- Such as thyroid medications and contraceptives.
- For example.
- So it’s important to tell your doctor so you can advise on the safe suspension of the drug for testing.
The T3 test is requested when the results of the TSH and T4 test change or when the person has symptoms of hyperthyroidism.As this is a hormone normally found in low blood concentrations, the dose of T3 alone is not widely used to evaluate thyroid function., normally requested when the diagnosis of thyroid failure is confirmed or in combination with TSH and T4.Learn about other tests that test your thyroid.
In addition to being helpful in helping with the diagnosis of hyperthyroidism, the T3 test may also be ordered to help identify the cause of hyperthyroidism, such as Graves’ disease, for example, and is usually requested with thyroid autoanticorp measurement.
The test is performed from a blood sample sent to the laboratory, which measures the concentration of total T3 and free T3, which corresponds to only 0.3% of the total T3, thus ending more in its combined form with proteins.The reference value for the total T3 is between 80 and 180 ng /dL and for the free T3 is between 2.5 – 4.0 ng/dL, which may vary by lab.
T3 values vary depending on a person’s health status and may increase, decrease, or normalize:
The results of the T3 test, as well as those of T4 and TSH, only indicate that there is some change in hormone production by the thyroid, and it is not possible to determine what is causing this dysfunction.Your doctor may order more specific tests to identify the cause of hiccups or hyperthyroidism, such as blood formula, immunological and imaging tests.
Reverse T3 is the inactive form of the hormone derived from the conversion of T4.The reverse T3 dose is not in demand, being indicated only for patients with severe thyroid diseases, with reduced T3 and T4 levels, but high levels of reverse T3 are detected.In addition, reverse T3 can be high in situations of chronic stress, HIV infection, and kidney failure.
The reference value of the reverse T3 for newborns is between 600 and 2500 ng / mL and from the 7th day of life, between 90 and 350 ng / mL, which can vary from one lab to another.