SHBG (Sex Hormone-Binding Globulin)
A transport protein whose level determines how much testosterone is actually 'available' to tissues — without knowing SHBG, a total testosterone result alone can be misleading.
Number of studies
1
Safety
Moderate
Time to effects
Not applicable — SHBG is a diagnostic parameter, not an intervention.
Who it's for
Table of contents
TL;DR
A transport protein whose level determines how much testosterone is actually 'available' to tissues — without knowing SHBG, a total testosterone result alone can be misleading.
- →Enables correct interpretation of a total testosterone result
- →Helps explain symptoms of testosterone deficiency despite an apparently normal total result
- →Points to possible underlying causes (thyroid disease, liver disease, insulin resistance)
| Type of compound | Transport protein produced in the liver |
|---|---|
| Level of evidence | Strong — well-characterized role in sex hormone pharmacokinetics |
| Target group | People interpreting testosterone results, especially in the context of TRT |
| What raises SHBG | Hyperthyroidism, liver cirrhosis, estrogens, aging |
| What lowers SHBG | Obesity, insulin resistance, hypothyroidism, exogenous androgens |
| Status | Standard parameter in hormonal diagnostics |
Understand
Overview
SHBG (sex hormone-binding globulin) is a protein produced mainly in the liver that binds testosterone and estradiol in the bloodstream, rendering them biologically inactive as long as they stay bound. Only the fraction of testosterone not bound to SHBG (and, to a lesser extent, to albumin) — known as free or bioavailable testosterone — can freely enter tissues and produce a biological effect.
SHBG's clinical importance comes from the fact that its level can differ substantially between people with the same total testosterone, leading to very different real-world hormone availability. Someone with high SHBG and a 'normal' total testosterone result can still have symptoms of deficiency, because the actually available testosterone is low — and vice versa, which is why interpreting total testosterone alone, without accounting for SHBG, can be misleading.
Who can genuinely benefit from this? Anyone interpreting hormone test results, especially in the context of suspected testosterone deficiency or TRT eligibility screening — a full assessment should include SHBG alongside total testosterone, and ideally a direct measurement or calculation of free testosterone as well.
Mechanism of action
SHBG is synthesized in the liver and released into the bloodstream, where it binds testosterone and estradiol with high affinity, forming a complex unable to cross the cell membranes of most tissues. SHBG levels are regulated by many factors — they rise with hyperthyroidism, liver cirrhosis, estrogen use, and age, and fall with obesity, insulin resistance, hypothyroidism, and exogenous androgen use.
Because only the free fraction of testosterone and the fraction loosely bound to albumin (so-called bioavailable testosterone) is capable of producing a biological effect in target tissues, changes in SHBG level translate directly into how much hormone is actually available, even when total testosterone concentration stays unchanged — which is why, when assessing hormonal status, clinicians increasingly recommend interpreting both parameters together rather than total testosterone alone.
Synthesis in the liver
SHBG is produced mainly in hepatocytes and released into the bloodstream.
Binding testosterone and estradiol
SHBG binds sex hormones with high affinity, rendering them biologically inactive.
Regulating biological availability
Only the free fraction of testosterone can enter tissues and produce a physiological effect.
Evidence: strong — based on 1 study in this database.
Benefits
Common myths
MythA normal total testosterone always means normal hormonal balance.
FactWith elevated SHBG, the actual, biologically available amount of testosterone can be low despite an apparently normal total testosterone result.
MythSHBG is a parameter without practical clinical relevance.
FactSHBG is a key element of correctly interpreting androgen status, especially relevant when symptoms are ambiguous despite an apparently normal total testosterone result.
Practice
Frequently asked questions
Low SHBG usually means more free, biologically available testosterone at the same total level, but it can also point to obesity, insulin resistance, or hypothyroidism as an underlying cause.
It isn't always part of the basic panel, but it's standardly recommended when working up symptoms suggesting testosterone deficiency, especially when the total testosterone result is ambiguous.
Yes — exogenous androgens, including testosterone replacement therapy, usually lower SHBG levels.
What to combine with
Good combinations
Testosterone — Interpreting SHBG only makes sense together with a total, and ideally free, testosterone result
Safety
Side effects & contraindications
Possible side effects
Contraindications
No significant contraindications at typical doses.
Interactions
Estrogens and estrogen-containing medications raise SHBG
Exogenous androgens (including TRT) lower SHBG
Is it worth taking?
Who it's for
- Men being worked up for hypogonadism
- People interpreting a full hormonal panel, not just a single result
Not for
- No significant contraindications at typical doses.
Evidence
Worth knowing
SHBG levels naturally rise with age, which partly explains the decline in bioavailable testosterone in older men despite a less dramatic drop in total testosterone.
Obesity and insulin resistance usually lower SHBG, which can mask a real testosterone deficiency in the total result alone.
Studies
SHBG concentration significantly modifies the amount of biologically available testosterone, making its measurement an essential part of correctly interpreting androgen status.
Selby C, Annals of Clinical Biochemistry, 1990
Sex hormone binding globulin: origin, function and clinical significance
Strong evidenceSelby C · Annals of Clinical Biochemistry · 1990
A classic review discussing the origin, function, and clinical significance of SHBG in interpreting hormonal status.
View studySources & bibliography
Citations are illustrative for this demo version and require full bibliographic verification by the editorial team before production publication.
Compare with similar entries
About the authors of this entry
Author
dr Piotr ZielińskiEndocrinologist
Piotr reviews content on hormones, metabolic health and supplement pharmacology.
131 publications on this site
Medical review
Michał NowakClinical Dietitian
Michał specializes in metabolic nutrition, intermittent fasting and sports supplementation.
61 publications on this site
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Comments (2)
- KW
Kasia W. 2 weeks ago
Very clearly explained, especially the interactions section — I hadn't seen it laid out this well anywhere else.
- MT
Marek T. a month ago
Are you planning to update this with the newest study from this year? I saw an interesting meta-analysis.