What does it measure?
The liver makes SHBG, which binds sex hormones including testosterone and estradiol. Bound and unbound hormone contribute differently to what tissues can use. Measuring SHBG helps explain why a total testosterone level may not match symptoms.
Before the test
- Sample
- A blood sample from a vein.
- Medicines
- Mention contraceptives, estrogen therapy, and other hormone medicines.
What can the result mean?
Higher SHBG can mean a smaller free fraction at a given total testosterone level; lower SHBG can mean a larger free fraction. Neither pattern diagnoses a hormone disorder on its own. SHBG is a carrier, not a hormone to raise or lower without a clinical reason. [1]
When is it useful, and how is it read?
Read SHBG when a testosterone result needs context, with symptoms, age, medicines, thyroid status, and liver health. The goal is to understand hormone availability and its cause, rather than to change the carrier number for its own sake. [1]
Reading the results together
| Marker | What it adds |
|---|---|
| Testosterone (Total) | Includes both bound and unbound testosterone. |
| Sex Hormone Binding Globulin (SHBG) | A carrier protein that affects hormone availability. |
| Free Androgen Index | A ratio using total testosterone and SHBG in selected assessments. |
An index is not a direct free-testosterone measurement. Read the method, symptoms, and medicines together. [1] [2]
What can affect it?
Age, pregnancy, estrogen medicines, thyroid function, liver health, and metabolic conditions can change the level. Total testosterone and, when appropriate, a validated free-testosterone estimate provide the missing context. [1]
The carrier can help explain a hormone mismatch
Two people with the same total testosterone can have different free fractions if their SHBG differs. That is one reason symptoms and a total hormone value may not line up neatly. [1]
Questions you might have
Can total testosterone look normal while availability differs?
Yes. Changes in SHBG affect how much testosterone is bound, so the total alone may miss part of the picture. [1]
Does SHBG alone diagnose PCOS?
No. It can add context, but symptoms and other findings are needed. [1]
What comes next?
Bring your medicine and supplement list, including hormonal treatments, to the review. Your clinician can decide whether SHBG explains an unexpected hormone result and whether any additional testing would actually change care. [1]
Could SHBG explain the difference between my total testosterone result and how I feel?
The reference interval and units on your report are part of understanding your result. Understand units, reference intervals, and treatment targets.
Sources & references
Medical references & original research
- MedlinePlus — SHBG blood test
- York and Scarborough Teaching Hospitals NHS — Free Androgen Index
- Mayo Clinic Laboratories. Testosterone, Total, Bioavailable, and Free, Serum (TTFB).
- Bhasin S, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology & Metabolism. 2018;103:1715–1744.
Books we consulted
References that informed our explanations of the test and its context.
- Rifai N, Chiu RWK, Young I, Burnham CAD, Wittwer CT, editors. Tietz Textbook of Laboratory Medicine. 7th ed. Elsevier; 2023.
Practical-section sources accessed: .
For general health education. Interpreting your result and deciding on tests or treatment requires your health context and a qualified clinician.
