SHBG Protein

SHBG binds to sex hormones, including testosterone, dihydrotestosterone (DHT), and estradiol, with varying affinities. It has the highest affinity for dihydrotestosterone, followed by testosterone and estradiol . This binding regulates the availability of these hormones to target tissues, thereby modulating their biological effects .

The synthesis and secretion of SHBG are primarily regulated by estrogen. Elevated estrogen levels, such as those seen during pregnancy, lead to increased SHBG production. Conversely, conditions associated with elevated androgen levels, such as polycystic ovarian syndrome (PCOS) and obesity, are often linked to decreased SHBG concentrations .

SHBG levels are used as a supplementary parameter in the assessment of androgen status. By calculating the Free Androgen Index (FAI), which is the ratio of total testosterone to SHBG, clinicians can estimate the amount of free testosterone in the blood . This is particularly useful in diagnosing conditions like hyperthyroidism, cirrhosis of the liver, and androgen receptor disorders .

The reference ranges for SHBG levels vary between males and females. For males, the range is typically between 13 and 71 nmol/L, while for females, it is between 18 and 114 nmol/L .

• Elevated SHBG Levels: Seen in elderly men, patients with hyperthyroidism, and those taking oral contraceptives or antiepileptic drugs .
• Decreased SHBG Levels: Associated with conditions like hypothyroidism, PCOS, obesity, hirsutism, and acromegaly .

In humans, SHBG is present in fetal blood early in gestation and correlates with testosterone levels, suggesting a role in male sex differentiation. Maternal plasma SHBG levels surge during mid to late pregnancy, possibly to protect the fetus from maternal sex steroids .