FT3 or free T3 test is done to assess thyroid disorders. Free triiodothyronine (FT3) may be measured in response to an abnormal TSH and/or FT4 result. It is a less reliable test for hypothyroidism and should rarely be used. It can be used for monitoring of patients on T3 therapy. TSH stands for thyroid stimulating hormone. A TSH test is a blood test that measures this hormone. TSH levels that are too high or too low may be a sign of a thyroid problem. The thyroid is a small, butterfly-shaped gland in the front of your neck. Your thyroid makes hormones that control how your body uses energy. Thyroid hormones affect nearly every organ in your body, including your heart. They help control your weight, body temperature, muscle strength, and even your mood. If you don't have enough thyroid hormones in your blood, many of your body functions slow down. If you have too much, many body functions speed up.