SHBG (Sex Hormone-Binding Globulin)

Hormones & Labs · Reviewed August 2026

Definition

SHBG, or sex hormone-binding globulin, is a protein made by the liver that binds testosterone and estradiol in the blood. Only the small unbound share of each hormone can act on tissues, so the amount of SHBG in circulation sets how much of these hormones is free.[1]

Educational content, not medical advice. For personal or fertility concerns, please consult your doctor.

What SHBG Measures

SHBG isn't a hormone. It's a carrier protein, made by the liver, that binds sex steroids with high affinity and specificity.[1][3] An SHBG test measures how much of this carrier is circulating in your blood. That number matters because of what it does to the hormones it binds. Researchers describe binding proteins like SHBG as gatekeepers: they regulate the free, unbound fraction of a steroid hormone, and it's that free fraction that can act on target tissues.[1] For testosterone, the effect is dramatic. Only 1% to 4% of circulating testosterone is free, and the rest travels bound to SHBG and albumin.[2] Estradiol rides the same carrier, so SHBG shapes the free share of both of the sex steroids people most often test.[1]

How It's Measured

SHBG is measured from a standard blood draw and usually reported in nmol/L. It rarely gets ordered alone. Panels typically pair it with total testosterone, because a total testosterone result counts bound and free hormone together and SHBG shows how much of that total is tied up by its main carrier. Labs and clinicians often use the pair to estimate the free testosterone fraction, which is why the two numbers tend to arrive on the same report.[2]

Why People Track SHBG

SHBG shows up on most hormone panels, including the at-home test kits that have made hormone testing common outside the clinic. It's the context number: the same total testosterone reading means something different depending on how much SHBG is in circulation, so tracking one without the other leaves the picture incomplete. Research also ties SHBG to a wide net of biology. Its levels are regulated by androgens, estrogens, thyroid hormones, and other metabolic factors, which is part of why it appears on panels well beyond reproductive health.[3]

If you're deciding between test kits or wondering what a panel actually covers, see our guide to at-home hormone tests.

How Go Go Gaia Tracks SHBG

SHBG comes from a lab blood draw, not from an app or wearable. Upload a lab report or enter a result by hand and Go Go Gaia stores it as SHBG in nmol/L, charted on a timeline next to the hormones it binds, like testosterone and estradiol, plus your cycle days and symptom logs. Repeat tests build a history in one place instead of scattered PDFs.

See your hormone panel in one timeline

Upload SHBG, testosterone, and estradiol results to Go Go Gaia and see them charted together over time.

Download Go Go Gaia

Free to download on the App Store.

What the Research Shows

Estrogen raises SHBG, and the clearest evidence comes from birth control research. A systematic review of 42 studies in nearly 1,500 healthy women found that combined oral contraceptives raised SHBG substantially, and free testosterone fell by about 61% on average, roughly twice the drop in total testosterone. The extra SHBG soaked up more of the circulating hormone.[4]

Metabolic health links to SHBG too. Observational studies have associated lower SHBG with insulin resistance and with a higher incidence of type 2 diabetes in both men and women, independent of sex hormone levels. These are population-level associations, not something a single reading can tell you.[5]

SHBG also isn't the only carrier estrogen pushes up. The same pattern holds for thyroxine-binding globulin, the protein that carries thyroid hormone.[6] Our TSH entry covers that side of the story.

Related Terms

Testosterone

The main androgen SHBG binds. Total testosterone counts both bound and free hormone in one number.

Free Testosterone

The unbound fraction of testosterone, often estimated from total testosterone and SHBG together.

Estradiol

The main ovarian estrogen. SHBG carries it in the blood, and estrogen in turn raises SHBG levels.

Insulin

The metabolic hormone that population research links to SHBG through insulin resistance.

Frequently Asked Questions

Educational information based on published sources. Not medical advice. For personal concerns, please consult your doctor.

Where is SHBG made?

The liver makes SHBG and releases it into the blood, where it binds sex steroids like testosterone and estradiol with high affinity. Because only the unbound share of a hormone can act on tissues, SHBG works as a gatekeeper that sets how much testosterone and estradiol circulate in free form.

Why do labs measure SHBG alongside total testosterone?

A total testosterone result counts both bound and free hormone together, and only 1% to 4% of circulating testosterone is free. SHBG shows how much of the total is tied up by its main carrier, which is why panels often report the two together and use them to estimate the free fraction.

Does hormonal birth control affect SHBG?

In studies of healthy women, combined oral contraceptives raised SHBG levels substantially, and free testosterone fell more than total testosterone as a result. That's a population-level research finding about estrogen-containing pills, not a statement about any individual result. For questions about your own labs or contraception, talk to your doctor.

References

  1. Hammond GL. Plasma steroid-binding proteins: primary gatekeepers of steroid hormone action. Journal of Endocrinology. 2016;230(1):R13–R25. PubMed: 27113851
  2. Goldman AL, Bhasin S, Wu FCW, Krishna M, Matsumoto AM, Jasuja R. A Reappraisal of Testosterone's Binding in Circulation: Physiological and Clinical Implications. Endocrine Reviews. 2017;38(4):302–324. PubMed: 28673039
  3. Thaler MA, Seifert-Klauss V, Luppa PB. The biomarker sex hormone-binding globulin – from established applications to emerging trends in clinical medicine. Best Practice & Research Clinical Endocrinology & Metabolism. 2015;29(5):749–760. PubMed: 26522459
  4. Zimmerman Y, Eijkemans MJC, Coelingh Bennink HJT, Blankenstein MA, Fauser BCJM. The effect of combined oral contraception on testosterone levels in healthy women: a systematic review and meta-analysis. Human Reproduction Update. 2014;20(1):76–105. PubMed: 24082040
  5. Wallace IR, McKinley MC, Bell PM, Hunter SJ. Sex hormone binding globulin and insulin resistance. Clinical Endocrinology (Oxford). 2013;78(3):321–329. PubMed: 23121642
  6. Chakravarthy V, Ejaz S. Thyroxine-Binding Globulin Deficiency. StatPearls [Internet]. StatPearls Publishing. NCBI Bookshelf: NBK544274

Sourced from peer-reviewed research and, for basic mechanism claims, established references like NIH and StatPearls. Every citation above is checked to confirm it resolves to a real source and supports the sentence it's attached to. Last reviewed August 2026. See our full methodology on the Encyclopedia hub.