This is a single-marker test measuring TSH. TSH is the most common test used to evaluate thyroid function and symptoms related to a thyroid disorder, such as hyperthyroidism or hypothyroidism. Produced by the pituitary gland, the primary role of TSH in the body is to stabilize amounts of T4 (thyroxine) and T3 (triiodothyronine) in the blood. NOTE: DHA Laboratory blood draws must be performed at Labcorp.