About Sex Hormone Binding Globulin
SHBG is a carrier protein produced by the liver that binds to testosterone and estradiol, controlling how much of each hormone is free and biologically active. High SHBG — common with aging, hyperthyroidism, and liver disease — can produce symptoms of low testosterone even when total testosterone appears normal. Low SHBG — associated with obesity, insulin resistance, and hypothyroidism — means more free hormone is available, which in women can contribute to androgen excess and PCOS symptoms.