TSH (thyroid stimulating hormone)

What this test is

TSH checks how your thyroid is working. It is the best first thyroid blood test. Your doctor may order it if you feel very tired, gain or lose weight, feel too hot or cold, or have hair loss or irregular periods. It is also checked in some cases with no symptoms, like before pregnancy, after having a baby, or if you take a medicine that can affect the thyroid. TSH is not needed as a routine test if you feel well and have no risk factors. Checking it just in case does not help healthy people. If TSH comes back abnormal, your doctor will add a free T4 test and talk with you about next steps.