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Formal name: Free triiodothyronine
Related tests: TSH; Total T4; FT4; Total T3

At a Glance

Why Get Tested?

To help diagnose hyperthyroidism and to monitor it's treatment

When to Get Tested?

If you get an abnormal thyroid stimulating hormone (TSH) or free thyroxine (FT4) result

Sample Required?

A blood sample taken from a vein in the arm

Test Preparation Needed?

None needed; however, certain medications can interfere with the FT3 test, so tell your doctor about any drugs that you are taking