Sex hormone-binding globulin (SHBG) (SHBG)

Sex hormone-binding globulin (SHBG), also known as testosterone-estradiol binding globulin, is a homodimeric glycoprotein primarily synthesized in the liver and released into the bloodstream (Hammond, 2011; Wikipedia, 2024). Its fundamental biological role is the high-affinity binding and transport of sex steroids, including testosterone, dihydrotestosterone, and estradiol, which regulates the concentration of free, biologically active hormones available to tissues (Rythm Health, 2025; Mayo Clinic, 2024). Beyond its function as a carrier protein, SHBG acts as a signaling molecule by interacting with a specific cell surface receptor (SHBG-R), where the subsequent binding of a steroid ligand triggers the activation of adenylate cyclase and increases intracellular cAMP levels (Rosner et al., 1991; PMC, 2011). Clinically, SHBG serves as a critical biomarker for metabolic and endocrine health; low serum levels are strongly associated with insulin resistance, metabolic syndrome, type 2 diabetes, and polycystic ovary syndrome (PCOS) (PMC, 2022; Superpower, 2025). Conversely, elevated SHBG levels are observed in conditions such as hyperthyroidism, liver cirrhosis, and during pregnancy or estrogen therapy (Wikipedia, 2024; Johns Hopkins, 2024). Pharmacological modulation of SHBG is a key strategy in managing hyperandrogenic states, with oral contraceptives containing ethinylestradiol being used to increase SHBG levels and thereby reduce free testosterone (Hammond, 2016; Ada Health, 2025). Understanding SHBG dynamics is essential for the accurate interpretation of hormone profiles and the optimization of therapies for reproductive and metabolic disorders (Rythm Health, 2025; Mayo Clinic, 2024).

Other names

Testosterone-estradiol binding globulinTeBGSex steroid-binding globulinSSBGAndrogen-binding proteinABPSex steroid-binding proteinSBPSex hormone-binding protein

SHBG regulates the bioavailability of sex steroids by sequestering them in the plasma, preventing their diffusion into cells (Hammond, 2011). It also functions as a ligand for the SHBG receptor (SHBG-R) on cell membranes; when a steroid binds to the SHBG-SHBG-R complex, it activates adenylate cyclase and increases intracellular cAMP levels, providing a non-genomic pathway for steroid action (Rosner et al., 1991).