Sex Hormone-binding Globulin (SHBG) is a transport protein that binds to testosterone and estradiol in the blood, regulating their bioavailability and biological activity. This test measures SHBG levels to evaluate hormonal balance and diagnose conditions affecting sex hormone metabolism. SHBG levels are influenced by various factors: estrogens and thyroid hormones increase SHBG production, while androgens suppress it. Low SHBG levels are associated with conditions of androgen excess such as hirsutism, polycystic ovary syndrome, and obesity, while elevated levels may indicate hyperthyroidism, liver disease, or pregnancy. SHBG measurements are particularly valuable for calculating the free androgen index, which provides a more accurate assessment of biologically active testosterone levels than total testosterone alone. This test helps distinguish between different causes of hormonal imbalance and guides appropriate treatment decisions.