TT4 thyroid total T4
T4, or TT4 total T4, is a thyroid hormone. This hormone ensures that all kinds of processes in the body run fast enough. A value that is too low indicates that the thyroid is working too slowly.
T4 is a hormone also called thyroxine. It is produced by the thyroid gland and helps metabolism and growth. T4 is often tested as part of thyroid function. The hormone T4 is a type of precursor. T3 is the active hormone. As needed by the body, tissues and cells, T4 is converted to T3. This happens in the liver, muscles and brain, among others.
Total T4 measures the total amount of thyroxine in the blood, including the portion bound to transport proteins. The proteins that help transport thyroxine through the blood are:
- Thyroxin binding globulin
- Albumin
- Transthyretin
Free T4 is the portion of thyroxine in the blood that is not bound to another protein. This is the part of the hormone that is effective and can affect different cells in the body.
Doctors can use the T4 determination to examine the thyroid gland. It is requested for symptoms that may indicate a thyroid condition. For example, with an overactive thyroid (hyperthyroidism), symptoms often include weight loss, rapid heartbeat and feeling agitated.
A slow-acting thyroid is called hypothyroidism, symptoms that fit this are weight gain and fatigue.
Too high a T4 indicates a thyroid that works too fast.
In general, the FT4 (free T4) is usually measured. T4 is often only on specific request.
With the introduction of FT4, the determination of TT4 and TT3 has no more value in the primary diagnosis of thyroid disorders. However, if the results of TSH and FT4 do not match the patient's complaints, determination of TT4 and TT3 can provide additional information.
When T4 is displaced from the binding proteins in plasma, an increased FT4 concentration is measured without causing hyperthyroidism. Determination of TT4 then has direct added value for the diagnosis.
Total T4 is also part of this test: https://bloodtesting.nl/schildklier-tsh-totaal-t4-en-totaal-t3/
