A T4 Total test is a blood test that measures the total amount of thyroxine (T4) hormone in your bloodstream, both bound and unbound.
There are several reasons why your doctor might order a T4 Total test:
Thyroid disease: T4 levels can be affected by thyroid disease. An underactive thyroid (hypothyroidism) can cause low T4 levels, while an overactive thyroid (hyperthyroidism) can cause high T4 levels.
Monitoring thyroid treatment: If you have been diagnosed with thyroid disease and are receiving treatment, such as medication to regulate thyroid hormone levels, your doctor may order a T4 Total test to monitor the effectiveness of your treatment.
Evaluating protein binding issues: T4 hormone is mainly bound to proteins in the blood, such as thyroxine-binding globulin (TBG), transthyretin, and albumin. In rare cases, certain medical conditions or medications can affect protein levels and cause changes in T4 Total levels.
It’s important to note that the T4 Total test measures both bound and unbound T4, and protein levels in the blood can vary. For this reason, the T4 Free test is often considered more accurate for assessing thyroid function. Your doctor will consider your specific medical history and symptoms when deciding which tests to order.