TSH

TSH, or thyroid-stimulating hormone, is the main blood test used to check how well your thyroid gland is working. It is a signal from the brain that tells the thyroid how much hormone to produce.

Because the thyroid affects energy, weight, mood and heart rate, an abnormal TSH can help explain symptoms such as fatigue or weight change and may indicate an underactive or overactive thyroid. It is often followed by Free T4 and Free T3.