# SHBG (Sex hormone-binding globulin)

SHBG (sex hormone-binding globulin) is a protein your liver makes that grabs and carries sex hormones in your blood. It binds about 44% of your testosterone and 30 to 60% of your estradiol tightly. (Albumin loosely carries another ~50% of testosterone, leaving just 1 to 4% truly free.) By holding hormones, SHBG controls how much is actually available to your tissues. Labs measure it by immunoassay, with ranges that depend on the platform (roughly 10 to 80 nmol/L in men, 20 to 130 in non-pregnant women); mass spectrometry is the reference method. SHBG falls with insulin resistance, obesity, type 2 diabetes, taking androgens, low thyroid, steroids, growth hormone, and advanced liver disease. It rises with estrogens, the pill, high thyroid, anorexia, and aging in men. Its main clinical use is correcting a total-testosterone reading by calculating free or bioavailable testosterone (the Vermeulen formula). One caution: assays vary enough to change the classification, so track it on the same platform over time.

## Sources

- Bhasin S, Brito JP, Cunningham GR, et al.. (2018). Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology & Metabolism. https://doi.org/10.1210/jc.2018-00229
- Vermeulen A, Verdonck L, Kaufman JM. (1999). A critical evaluation of simple methods for the estimation of free testosterone in serum. Journal of Clinical Endocrinology & Metabolism. https://doi.org/10.1210/jcem.84.10.6079
- Adaway J, Keevil B, Miller A, Monaghan PJ, Merrett N. (2019). Ramifications of variability in sex hormone-binding globulin measurement by different immunoassays on the calculation of free testosterone. Annals of Clinical Biochemistry. https://doi.org/10.1177/0004563219888549

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