Sex hormone-binding globulin: protein that binds testosterone and oestradiol.
What it is
SHBG in nmol/L. Used with total testosterone to refine how much hormone is free/active.
Sex hormone-binding globulin is a liver-made glycoprotein that binds testosterone and oestradiol with high affinity. Reported in nmol/L. Free androgen index or calculated free testosterone uses SHBG with total testosterone when binding is abnormal.
Why it matters
SHBG rises with oestrogen, pregnancy, and some thyroid states; falls with insulin resistance, androgens, and obesity. Interpreting testosterone without SHBG can mislead when binding is abnormal.
This guide is educational only and cannot diagnose you. Discuss results, especially anything outside your laboratory’s reference interval, or that does not match how you feel, with a GP or other appropriately qualified clinician.
High SHBG (oestrogen, pregnancy, hyperthyroidism, ageing in men) can lower free testosterone despite a “normal” total. Low SHBG (insulin resistance, obesity, hypothyroidism, androgens, NAFLD) raises free fraction. Interpreting testosterone without SHBG misses this physics.
This guide is educational only and cannot diagnose you. Discuss results, especially anything outside your laboratory’s reference interval, or that does not match how you feel, with a GP or other appropriately qualified clinician.
How it affects the body
Only unbound (and albumin-bound) sex hormones readily enter cells; SHBG adjusts the free fraction.
Only unbound and loosely albumin-bound sex hormones readily enter cells to bind androgen or oestrogen receptors. SHBG is the adjustable buffer that sets how much hormone is free for a given total.
For athletes
Athletes with PCOS pathways, anabolic steroid history, or metabolic syndrome need SHBG in the hormone story: totals alone can deceive.
Athletes exploring low energy, PCOS-type symptoms, or post-steroid recovery should insist on SHBG with testosterone. Metabolic syndrome in masters athletes often pairs low SHBG with other cardiometabolic markers.
For fertility planning when you want AMH with key reproductive and thyroid markers in one private panel. AMH does not predict natural conception chances.
