SHBG (Sex Hormone-Binding Globulin)

Sex hormone-binding globulin (SHBG) is a protein produced by the liver that binds to testosterone and estrogen in the bloodstream, controlling how much of these hormones remain 'free' (unbound) and biologically active. Women with PCOS typically have low SHBG levels—driven down by insulin resistance and excess insulin—which means a greater proportion of their testosterone circulates freely and can act on tissues, amplifying androgen-related symptoms like hirsutism and acne even when total testosterone levels appear only mildly elevated. The free androgen index, calculated from total testosterone and SHBG levels, is often a more sensitive diagnostic marker for PCOS than total testosterone alone.