What is SHBG?
Sex Hormone Binding Globulin (SHBG) is a glycoprotein produced primarily by the liver that binds tightly to sex hormones in the bloodstream , particularly testosterone and estradiol. When testosterone is bound to SHBG, it is biologically inactive: it cannot enter cells, bind to androgen receptors, or produce the physiological effects associated with testosterone. Only the unbound fraction , called free testosterone , is bioavailable and capable of acting on target tissues. SHBG is therefore the gatekeeper that determines how much of your total testosterone is actually usable.
A standard testosterone panel measuring only total testosterone can be misleading in either direction. A person with total testosterone of 650 ng/dL and very high SHBG may have lower free testosterone bioavailability than someone with total testosterone of 450 ng/dL and low SHBG. This is why SHBG must be measured alongside total testosterone , and why researchers investigating testosterone-adjacent peptides like GH secretagogues (which lower SHBG) or libido peptides need to understand the full picture of hormonal bioavailability before and during any protocol.
What do the numbers mean?
Women 40–80 nmol/L
Women 18–144 nmol/L
SHBG is strongly influenced by thyroid status, insulin levels, estrogen, and liver function , a single SHBG value should always be interpreted alongside total testosterone, free testosterone, TSH, and fasting insulin for full clinical context.
Why this marker matters before peptide research.
The most clinically relevant insight from SHBG in a peptide research context is its relationship with growth hormone. GH and IGF-1 are established regulators of SHBG , elevated GH activity tends to lower SHBG, which increases free testosterone bioavailability without changing total testosterone. This is one of the documented secondary effects of GH secretagogue protocols in research: men who begin a GH secretagogue protocol often see their free testosterone improve even without any direct testosterone intervention, purely because SHBG has decreased. Understanding baseline SHBG before a protocol allows researchers to observe and attribute this effect accurately.
For men with high SHBG and low-normal total testosterone, SHBG context transforms the interpretation of their hormonal picture. A man with total testosterone of 500 ng/dL but SHBG of 65 nmol/L may have free testosterone in a deficiency range , explaining symptoms that a total testosterone result alone would not account for. Kisspeptin-10 and PT-141 research in the context of sexual function becomes more interpretable when SHBG is part of the baseline, since the subjective endpoints (libido, arousal response) are sensitive to free testosterone status.
Low SHBG is equally informative. Very low SHBG in men (below 10–15 nmol/L) is commonly associated with insulin resistance, obesity, and metabolic syndrome , the same constellation that GLP-1 peptide research targets. A low SHBG alongside elevated fasting insulin and high HbA1c creates a coherent metabolic picture that contextualizes why GLP-1 and metabolic peptide research may be relevant in a given individual.
How to get this test.
Where to order
Available at LabCorp, Quest Diagnostics, and through a physician. Less commonly included in standard panels , typically requires explicit ordering. Available through some direct-to-consumer hormone panels without a prescription.
How to prepare
Draw in the morning (7–10 AM) alongside total and free testosterone for the most useful picture. No fasting strictly required for SHBG alone, but fasting is recommended when ordering with testosterone and insulin simultaneously.
What to ask for
"SHBG" or "Sex Hormone Binding Globulin." Always order alongside total testosterone and free testosterone. Adding TSH and fasting insulin creates a complete hormonal and metabolic context panel in a single blood draw.