A thyroid function test measures the levels of thyroid-related hormones in your bloodstream. It can be used to detect an underactive thyroid (yypothyroidism) which can cause unexplained weight gain, persistent fatigue, cold sensitivity, dry skin, muscle weakness, or brain fog.

The test can also detect overactive thyroid (hyperthyroidism). Symptoms can include sudden weight loss, rapid or irregular heartbeat, anxiety, hand tremors, sweating, or heat intolerance.

It can also be a useful text to monitor medication dosages and track known thyroid nodules.