It is important to know how to interpret low t4 levels in order to understand what is going on with a person’s body. This t4 amount is normally combined with the TSH or thyroid stimulating hormone. Combining both the T4 and TSH results is essential for diagnosing and treating a problem with the thyroid. For many people with thyroid issues, the TSH does reveal exactly what is going on its own. The two different thyroid hormones, T4 and T3, are directly produced by the thyroid gland and secreted into the blood stream.
A low T4 thyroid hormone is just the first test. The T4 is also known as thyroxine or tetraiodothyronine. The second word is a long and much more fancy way of saying that T4 contains four iodine molecules attached to a central protein. There is a lot more T4 made in the thyroid than T3. People generally take a man made version of T4, which is called levothyroxine. This medicine is the fundamental treatment for people with hypothyroidism. The T4 that is made by the patients body cannot be differentiated from T4 provided by medication that you take by mouth. The medicine can be help a low t4 normal TSH. There are several ways to measure T4 in the blood.
The Total T4 is the assessment of the total amount of thyroxine that is present in the blood. This includes T4 that is carried on proteins and circulates as well as the free T4 that freely floats throughout the blood stream and is available to be converted to T3. Because T4 tends to be bound to proteins, any slight modification of the levels of these proteins can have a profound effect on total T4 levels. In patients taking estrogen supplementation in the form of hormone replacement therapy or birth control medication, the total T4 may appear to be higher than it actually is. This is because these medicines can elevate the amount of carrier proteins. This can also happen during pregnancy. A person who has a true elevation in their thyroid called hyperthyroidism, will have larger increases in total T4, while patients who have not been properly treated for their problems with hypothyroidism may show low levels of total T4, making the diagnosis.
When you get the results of the tests you should know the normal ranges for T4. A normal level for total T4 is about 4.8 to 10.4 mcg/dl in adults. This is micrograms per deciliter, a very small amount. Any higher level should be considered in the clinical context. For example, something slightly higher would be considered normal in pregnancy due to the changes in protein-binding that come from a developing fetus. In these cases it would be important to have a complete work up for low t4 levels to figure out the full problem.