SHBG -- What It Measures

Introduction

Understanding SHBG

SHBG is a protein that circulates in the blood and attaches to sex hormones. Because it binds testosterone, it is commonly measured together with total and free testosterone to add context to a hormone panel. This page explains, in plain language, what SHBG is, why it is commonly measured, and how it relates to the testosterone markers.

Everything here is educational context. It does not interpret what any particular value means, does not diagnose, and does not describe any course of action.

What it measures

What SHBG is

SHBG stands for sex hormone-binding globulin.
It is a hormone-binding protein made mainly by the liver.
It binds sex hormones, including testosterone and estradiol, and carries them in the blood.
Because SHBG binds testosterone, it can influence how much testosterone remains as the unbound fraction.

SHBG binds testosterone with strong affinity, so testosterone attached to SHBG is generally considered unavailable to tissues. Albumin also binds some testosterone, but more loosely. The small portion attached to neither protein is the unbound (free) fraction.

Educational context

Why SHBG is commonly measured

SHBG is commonly measured as part of a broader look at hormone status, usually together with total and free testosterone. In research and clinical education it adds context in several ways:

Hormone panels — SHBG is a routine companion marker when testosterone is ordered.
Testosterone context — because SHBG binds testosterone, it helps describe how the total amount is distributed.
Free testosterone context — SHBG is one of the inputs used when free testosterone is estimated.
Total vs free context — SHBG helps explain the relationship between the total measurement and the unbound fraction.
Sex and age context — SHBG differs by sex and can vary with age, so it is read within the context of the individual.
Lab-method context — assays and units vary between laboratories.

This page does not interpret what any particular value means and does not recommend any action. Any individual measurement should be discussed with a licensed healthcare provider.

Relationship

Relationship to testosterone biomarkers

SHBG is most useful when read alongside the testosterone markers, because it helps explain how they connect:

Total Testosterone measures the combined amount — both bound and unbound testosterone.
Free Testosterone measures only the unbound fraction.
SHBG helps explain why total and free testosterone may not move together: when more testosterone is bound to SHBG, a smaller proportion circulates as free testosterone.
Albumin also binds some testosterone, more loosely than SHBG.

For a broader view of how these markers fit together, see the Testosterone Overview.

Units

Common units

SHBG is most often reported in nmol/L (nanomoles per liter). Units and assay methods vary by laboratory, so always read the unit printed next to your own measurement.

Reference

Public reference example

The figure below is a public reference example drawn from a published source and labeled by the study population it came from. It is shown for educational context only.

Public reference example · adult study population (ages 40 and older)

12.6 – 92.4 nmol/L

From published reference intervals in 1,477 healthy adults ages 40 and older (NHANES, chemiluminescence assay). This example is not sex-specific. Source: Endotext (Winters), Laboratory Assessment of Testicular Function.

SHBG reference ranges vary by laboratory, assay, age, sex, and population. This is a public reference example for education, not a universal standard and not a determination about any individual. Where a measurement is available, Pepvela prioritizes the reference range printed on your own lab report.

Related biomarkers

These related biomarkers are often reviewed alongside SHBG for educational context:

Total Testosterone Free Testosterone Testosterone Overview LH and FSH DHEA-S Estradiol

Related peptide research

Research literature involving certain compounds may measure testosterone-related or hormone-related markers as endpoints. The following research pages are provided for educational context only and make no claim about any effect on testosterone or SHBG:

Gonadorelin A research compound studied in the reproductive axis, where hormonal-axis markers are sometimes measured as endpoints.

Kisspeptin-10 A research compound whose literature may include reproductive-axis or hormone-related endpoints.

HCG Studied in research contexts where testosterone-related markers are sometimes measured.

Sermorelin A growth-hormone-axis research compound; hormonal-axis markers are sometimes measured alongside it.

Research: Understanding Your Biomarkers →

Citations

MedlinePlus. SHBG Blood Test. U.S. National Library of Medicine. https://medlineplus.gov/lab-tests/shbg-blood-test/
Winters SJ. Laboratory Assessment of Testicular Function. Endotext. NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK279145/
Thaler MA, Seifert-Klauss V, Luppa PB. The biomarker sex hormone-binding globulin - from established applications to emerging trends in clinical medicine. Best Pract Res Clin Endocrinol Metab. 2015;29(5):749–760. https://pubmed.ncbi.nlm.nih.gov/26522459/

SHBG - What It Measures and Why It Is Tracked