SHBG

Sex hormone-binding globulin. The protein that holds testosterone out of circulation. Often low in PMOS, which raises free testosterone even when total looks normal.

RN-reviewed

SHBG (sex hormone-binding globulin) is a protein made by the liver. Its job is to bind sex hormones, testosterone in particular, and hold them out of circulation. When testosterone is bound to SHBG, it is biologically inactive. When SHBG levels are low, more testosterone is free, moving around the body and reaching tissues like the skin and hair follicles.

In PMOS, SHBG is often low. The mechanism is insulin: high insulin signals the liver to make less SHBG. Less SHBG means more free testosterone, even when the total testosterone result on the lab panel looks normal.

This is one of the reasons "your testosterone is normal" can sit next to a body that clearly is not. Total testosterone is the testosterone tied up plus the testosterone free. Free testosterone, the one doing things in the body, can be elevated even when total looks fine.

SHBG and free testosterone (or free androgen index) are both worth asking about if you have androgenic symptoms with a normal total testosterone. They are not standard on every lab panel; you may need to request them by name.

See also
GlossaryInsulin resistanceGlossaryFree testosteroneMechanismWhy PMOS Raises Androgens
Sources
  1. He Z, et al. Tissue-by-tissue insulin signalling and SHBG suppression in PCOS. 2023.
  2. Teede HJ, Misso ML, Costello MF, et al. International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. Monash University Centre for Research Excellence in PCOS. 2023.
Note

Reviewed by Mary Kristine Zabala, RN, EMHI before publication.

This is plain-language definition copy, not medical advice. For decisions about your care, talk to a clinician who knows your history.