Lately, there's some confusion about the T3 uptake test, a test considered obsolete. This test doesn't measure thyroid hormone. In this test, T3 is used as a reagent to determine how well your binding (carrier, transport) proteins bind with thyroid hormone. Years ago, this result was used along with the T4 test result to get an idea of about how much free T4 was present. This calculated result is referred to as an FTI or an FT7. Today, free T4 is tested using the direct FT4 test. 

What often happens is that the doctor checks the T3 uptake box mistaking it for the FT3 test. In some cases, lab staff transpose the order incorrectly.

A high T3 uptake isn't a sign of thyroid disease. A high uptake is caused by estrogens and a low uptake can be seen in malnutrition. The total T4 result measures free thyroxine (T4) that's linked to binding protein. In this form, thyroid hormone is inactive. The T4 result can be elevated because of increased free hormone or increased binding proteins. During pregnancy the uptake is elevated, and it's elevated in women on oral contraceptives or hormone replacement therapy.