T4

You should get a T4 test if you have symptoms of hypothyroidism, such as fatigue, weight gain, dry skin, hair loss, or cold intolerance, or of hyperthyroidism, such as weight loss, palpitations, anxiety, or heat intolerance. It is also recommended when TSH is abnormal, during pregnancy, and for monitoring thyroid medication.

No special preparation or fasting is required for a T4 test. Give your sample in the morning, and take your thyroid medicine after the sample unless your doctor advises otherwise. Stop biotin supplements 48–72 hours before the test, as biotin can interfere with results. Inform your doctor about pregnancy, oral contraceptives, or steroids.

No, fasting is not required for a T4 test. You can eat and drink normally before giving your sample. A morning sample is preferred, and you should take your thyroid medicine after the test unless your doctor advises otherwise. Stop biotin supplements 48–72 hours beforehand, as biotin can affect results.