The test for sex hormone binding globulin (SHBG) is ordered mainly along with other tests (primarily testosterone) to assess the androgen levels - the male hormones. With women the concern is excess testosterone production.

In women, there are small amounts of testosterone. The slightest increases in testosterone production can alter the equilibrium of hormones, resulting in symptoms such as lack of menstruation (amenorrhea), infertility, acne, and male pattern hair growth (hirsutism). These symptoms are usually (but not exclusively) associated with polycystic ovarian syndrome, a condition characterized by an excess production of androgens.

The Free Androgen Index (FAI),which is calculated by dividing total testosterone by SHBG, reflects the quantity of testosterone that is not bound (bioavailable testosterone) to SHBG and is calculated as follows: FAI = Total Testosterone / SHBG. An elevated FAI may be useful in the evaluation of androgenic alopecia (balding), hirsutism, and severe acne where testosterone levels may be normal.
Depending on your case, your treating physician may choose to prescribe treatment (anti androgens or other). Discuss these results with your doctor.