Pitfalls in the interpretation of TSH; a clinician perspective
The thyroid gland plays a major role in metabolism, growth and development. It helps to regulate many body functions by releasing thyroid hormones (thyroxine and triiodothyronine) into the bloodstream. Hypothalamic–pituitary–thyroid axis regulates secretion by negative feedback loop; hypothalamus senses low circulating levels of thyroid hormones and responds by releasing thyrotropin-releasing hormone. It stimulates the anterior pituitary to produce thyroid-stimulating hormone (TSH). The TSH, in turn, stimulates the thyroid to produce thyroid hormone until levels in the blood return to normal. TSH is a cornerstone of thyroid regulation. Clinically, TSH is used to help diagnose thyroid disorders, to monitor treatment of hypothyroidism and hyperthyroidism, to screen newborns for congenital hypothyroidism and to distinguish primary vs. secondary thyroid disease (or sick euthyroid syndrome) using for the interpretation of other hormones. The TSH typically takes six to eight weeks to accurately reflect thyroid hormone status after a change in therapy. In this lecture, beyond the described background of TSH secretion, clinical pitfalls in the interpretation of TSH are presented through 6 different clinical cases.