As a newly graduated clinician, my supervising physician taught me that the thyroid-stimulating hormone (TSH) levels of patients undergoing thyroid replacement therapy should be kept between 0.5 and 1.5 mU/L. Is this correct? I have since found no evidence in the literature to support or refute this advice.

Measuring TSH is the best way to monitor patients on thyroid replacement therapy for hypothyroid conditions. The general rule of thumb is to maintain the level between 1.0 and 2.0-2.5 mU/L, but make sure you pay attention to the patient’s overall state of health; together, TSH and patient condition are the best indicators of successful replacement therapy. For more information, see Williams Textbook of Endocrinology (11th ed. Philadelphia, Pa.: WB Saunders; 2007) and J Clin Endocrinol Metab 2002;87:489-499.
—Claire Babcock O’Connell, MPH, PA-C