What is T4 Free (FT4) test?
The unbound or free thyroxine hormone FT4 is the active fraction that is readily available for uptake into cells whereas the bound hormone, T4 on the other hand, represents a circulating storage pool that is not immediately available for uptake into cells.
Why get the T4 Free (FT4) test?
Free T4 helps in determining thyroid dysfunction in patients with symptoms of hypothyroidism or hyperthyroidism with normal TSH values. Free T4 measurements can be useful to determine appropriate dose increases or decreases in those taking medication for thyroid disorders when TSH is very high or low. FT4 and T3 are usually elevated with low TSH in hyperthyroidism.
When to take this test?
AnytimeEvery 6 monthsNo particular precautions are required, unless it is recommended by your doctor.FT4