Thyroid function tests are common tests used to tell how well your thyroid is working.
See the following articles for details:
Kim M, Ladenson P. Thyroid. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 233.
Salvatore D, Davies TF, Schlumberger MJ, Hay ID, Larsen PR. Thyroid physiology and diagnostic evaluation of patients with thyroid disorders. In: Melmed S, Polonsky KS, Larsen PR, Kronenberg HM, Larsen PR, eds. Williams Textbook of Endocrinology. 12th ed. Philadelphia, Pa: Saunders Elsevier;2011:chap 11.