Free Thyroxine T4 Levels. High levels of any of these tests (total t4, free t4, or free t4 index) may indicate an overactive thyroid, also known as hyperthyroidism. Your physician may order a test called total t4 or total thyroxine.
A free t4 level in the optimal range usually indicates normal thyroid gland function. However, changes in binding proteins can occur which affect the level of total t4 but leave the level of unbound hormone unchanged. Abnormally low free t 4 levels may signal hypothyroidism.
The normal ranges are as follows:
While total t4 is a relatively reliable indicator of t4 levels in the presence of normal binding proteins, it is not a reliable indicator when binding proteins are abnormal. Doctors in 147 specialties are here to answer your questions or. A free t4 level in the normal range is usually accompanied by a tsh level that is also in the normal range. This is also called hyperthyroidism.
