What is SHBG?
Written by Dr Robin Wang
SHBG stands for sex hormone binding globulin. It is a protein made by the liver that binds testosterone and oestradiol in the blood and carries them around the body. Most of the sex hormone circulating at any moment is attached to it.
Why does SHBG matter?
Only the unbound part leaves the bloodstream, enters tissues and acts, so the amount of SHBG present sets how much of the testosterone and oestradiol in circulation is available at all.
How does SHBG relate to other markers?
Total Testosterone counts every molecule in circulation, bound or not, and SHBG says how much of that total is held. Free Testosterone and FAI, the Free Androgen Index, are not separate measurements but calculations that combine those two figures. SHBG binds oestradiol, and oestradiol raises how much SHBG the liver makes.
What affects SHBG?
Thyroid activity pushes the liver to produce more SHBG. Higher body weight pushes production down, and so does insulin. SHBG rises with age, pregnancy raises it steeply, and liver disease lowers it.
Why Do Health tests SHBG once a year
The liver adjusts production over months as thyroid activity and body weight shift, so SHBG drifts across a year rather than changing from one week to the next. A yearly measurement keeps the SHBG figure current for the Free Testosterone and FAI calculations built on it. This is Do Health's monitoring schedule, not a general recommendation for everyone.
How does my SHBG compare?
Source
Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline
pubmed.ncbi.nlm.nih.govReviewed
Dr Robin Wang · 01/10/2026
British physician, Clinical Lead at Do Health
More in Hormones
All the testosterone in the blood, showing how much the body makes.
Learn more about Total TestosteroneThe part of testosterone the body can use.
Learn more about Free TestosteroneA hormone from the brain that controls milk production and can affect periods and fertility when high.
Learn more about ProlactinA hormone from the brain that tells the ovaries to develop eggs and the testes to make sperm.
Learn more about FSHA hormone from the brain that tells the ovaries to release an egg and the testes to make testosterone.
Learn more about LHThe main form of oestrogen, which controls the menstrual cycle and helps protect bones.
Learn more about OestradiolA score that estimates how much testosterone is free for the body to use.
Learn more about FAIOne membership.
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