Thyrotropin, or thyroid-stimulating hormone (TSH), is one of a family of glycoprotein hormones including luteinizing hormone (LH), follicle-stimulating hormone (FSH), and human chorionic gonadotropin (hCG) that share a common ⍺-subunit and a unique β-subunit. Pituitary TSH regulates the secretion of the thyroid hormones T₄ (thyroxine) and T₃ (triiodothyronine). TSH secretion, in turn, is controlled through negative feedback by thyroid hormone on the pituitary thyrotrope. This relationship is negative log-linear.<sup>79 Spencer C.A., LoPresti J.S., Patel A. , et al. Applications of a new chemiluminometric thyrotropin assay to subnormal measurement J Clin Endocrinol Metab 1990 ;  70 : 453  [cross-ref]

Cliquez ici pour aller à la section Références</sup> Small changes in serum free thyroid hormone concentrations result in large changes in serum TSH concentrations, and even subtle changes in thyroid hormone production are best assessed by measurement of serum TSH (Figure 1). Until the late 1980s, the detection limit of TSH assays was within the normal range, and these first-generation TSH assays were useful only for the detection of hypothyroidism. Free T₄ measurements were primarily used for assessing thyroid function despite the technical difficulties in free thyroid hormone measurements owing to abnormal binding proteins, changes in binding protein concentrations, and the effects of drugs and illness on thyroid hormone binding.<sup>83 Stockigt J.R. Free thyroid hormone measurement Endocrinol Metab Clin North Am 2001 ;  30 :

Cliquez ici pour aller à la section Références</sup> With the use of sensitive second- and third-generation TSH assays, TSH measurement has emerged as the single most useful test of thyroid function. It is widely and appropriately used as a screening test. Unfortunately, the trend has been to rely on TSH measurements alone for the assessment of complicated thyroid disease and patients undergoing treatment for thyroid dysfunction. This article focuses on the potential and real limitations of TSH measurement.