SHBG
Sex Hormone-Binding Globulin, What Raises It, What Lowers It, and Why Free Testosterone Depends On It
Evidence grade 4 of 5, Strong. Read how the Atlas grades evidence.
The written rationale for this grade is still being prepared.
- FDA
- N/A (endogenous protein / lab measure)
Reference only. Not medical advice.
What can go wrong
Misinterpretation risk rather than direct physiological risk: relying on total testosterone alone without SHBG can both over-diagnose hypogonadism (in low-SHBG men) and miss it (in high-SHBG men), leading to inappropriate treatment decisions.
This is something to take to a clinician. The Atlas can tell you what is known about shbg in general. It cannot tell you what is happening in your body, and the difference matters most for exactly the symptoms that bring people to this page.
Sex hormone-binding globulin (SHBG) is a liver-produced protein that binds testosterone tightly in the blood. Only the unbound (free, ~2-3%) and loosely albumin-bound fractions are biologically available; SHBG-bound testosterone (40-45%) is inert. This is why total testosterone can be normal while free testosterone is low (high SHBG), or why total can look low while free is adequate (low SHBG). Understanding what raises and lowers SHBG is essential to interpreting any testosterone lab, and it explains apparent contradictions that drive both over- and under-treatment.
The protein that decides how much of your testosterone is actually available.
What people take it for
What it is taken for. Approval, where it exists, covers only some of these.
How it works
SHBG binds testosterone and estradiol with high affinity, sequestering them from tissue uptake. Hepatic SHBG production is regulated by hormonal and metabolic signals: estrogen and thyroid hormone increase it; insulin and androgens suppress it. Because SHBG sets the ratio of bound to free hormone, two men with identical total testosterone can have very different free (active) testosterone depending on their SHBG.
Why total testosterone alone can mislead
RAISES SHBG: aging, hyperthyroidism, estrogen (including from obesity-driven aromatization in some contexts), liver disease/cirrhosis, anorexia/severe caloric restriction, certain anticonvulsants, and HIV. LOWERS SHBG: obesity and visceral adiposity, insulin resistance and type 2 diabetes, hypothyroidism, exogenous androgens and growth hormone, and nephrotic syndrome. The clinical trap: a lean, hyperthyroid, or older man with high SHBG may have normal total testosterone but symptomatic LOW free testosterone, while an obese, insulin-resistant man may show low total testosterone driven largely by suppressed SHBG with relatively preserved free fraction. Measuring free testosterone (ideally by equilibrium dialysis or calculated from total T, SHBG, and albumin) resolves the discordance, which is why the Endocrine Society includes SHBG in the workup.
Safety in detail
SHBG and free testosterone interpretation should be performed by a qualified physician; treatment decisions based on total testosterone alone, without accounting for SHBG, can be misleading.
What it does to fertility
SHBG itself is not a fertility intervention, but accurate free-testosterone interpretation prevents inappropriate exogenous testosterone treatment that would suppress fertility in men who are not truly deficient.
What has to be monitored
The bloodwork this needs, and the reason it belongs with a clinician rather than a website.
- SHBG with total testosterone
- Free testosterone (equilibrium dialysis or calculated)
- Albumin (for calculated free T)
- Thyroid function and metabolic assessment as SHBG modifiers
What people get wrong
Often saidA normal total testosterone rules out a problem
ActuallyHigh SHBG can leave free (active) testosterone low despite a normal total; symptoms with a normal total warrant SHBG and free testosterone measurement.
Often saidA low total testosterone always means you need treatment
ActuallyIn obese, insulin-resistant men, low total testosterone is often driven by suppressed SHBG with preserved free testosterone, addressing weight and insulin resistance may matter more than exogenous hormone.
Who profits, and who pushes back
Nobody is named here yet, because we have not done that work on this entry. Read that as unfinished. Somebody almost certainly sells this, and somebody almost certainly disputes it. Assume both until we have checked.
At a glance
- Source
- Liver
- Binds
- ~40-45% of total T (inactive)
- Free T
- ~2-3% (active)
- Key driver up
- Aging, thyroid excess, estrogen
- Key driver down
- Obesity, insulin resistance
What this entry does not yet cover
What follows is unfinished work on our side, not a finding about SHBG. A short entry is not a safe entry.
- Timeline. We have not built the dated record of research and regulatory events.
- Cost and market. We have not documented what it sells for or who sells it.
- Supply chain. We have not mapped where it is made.
- Who uses it. We have not documented the user groups.
- What could change. No forward-looking summary yet.
- How it compares. We have not set it against the alternatives.
- Children and teenagers. We have not checked what is known about younger people.
- Where we land. We have not taken a position on this yet.
Sources
The studies below are named and described, but not linked. You cannot open them from here and check our reading against them, which means this page is our summary of the literature rather than a document you can verify. Weigh it accordingly until the links exist.
The studies that matter
Endocrine Society Guideline (Bhasin et al.)2018
Recommends SHBG and free testosterone when total testosterone is borderline or discordant with symptoms