What is the Origin of SHBG Ratio?

This index originated in clinical endocrinology as a practical, cost-effective method to approximate the free hormone level without resorting to the more technically demanding direct free hormone assays. SHBG, a glycoprotein synthesized by the liver, is the key binding protein for sex hormones, and its concentration is a major determinant of hormone bioavailability. The term simply denotes the mathematical relationship between the total hormone and its primary binder.

What is the Mechanism of SHBG Ratio?

SHBG strongly binds to sex hormones, particularly testosterone and estradiol, reducing their biological activity. When SHBG levels are high, a larger proportion of the total hormone is bound and inactive, resulting in a lower SHBG Ratio and potential symptoms of deficiency, even with normal total hormone levels. Conversely, low SHBG increases the free fraction, potentially leading to symptoms of excess. The ratio thus functions as an inverse indicator of binding capacity, helping to explain clinical symptoms that may not align with total hormone concentrations.

SHBG Ratio ∞ Area

SHBG Ratio

Meaning

The SHBG Ratio, typically calculated as the ratio of Total Testosterone to Sex Hormone Binding Globulin (SHBG), is a clinically derived index used to estimate the bioavailable fraction of sex hormones. This ratio serves as a practical surrogate marker for free testosterone or free estradiol, offering insight into the amount of hormone readily available to exert its biological effects on target tissues. It is a critical metric for assessing androgen and estrogen status in both men and women, especially when direct free hormone measurement is unavailable.