- Made by
- Mostly the liver
- Binds
- Testosterone and estrogen
- Often lowered by
- Obesity, insulin resistance, hypothyroidism
- Often raised by
- Oral estrogen, hyperthyroidism, liver disease
Bound, loosely bound and free
Most testosterone in the blood is attached to proteins. Some is held tightly by SHBG, some is held loosely by albumin, and a small fraction floats free. The free and loosely bound portions are the hormone your muscles, brain and other tissues can readily use.
A standard total testosterone test counts all of it together. SHBG tells you how much of that total is locked away.
When SHBG runs low
- Obesity, insulin resistance and type 2 diabetes.
- Underactive thyroid.
- Use of anabolic steroids or other androgens.
- Cushing's syndrome.
- Polycystic ovary syndrome in women, where low SHBG can increase free testosterone and symptoms such as acne or excess hair.
When SHBG runs high
- Liver disease and an overactive thyroid.
- Estrogen-containing medicines, including oral menopause hormone therapy and birth control pills.
- Eating disorders or very low body weight.
Why it matters for testosterone results
The Endocrine Society recommends measuring free testosterone, by an accurate method or a validated calculation, when SHBG is likely altered or total testosterone is near the lower limit. A man with high SHBG may have a total testosterone in range but low free testosterone and genuine symptoms. A man with obesity may have a low total but a free level that is closer to normal.
MedlinePlus notes that SHBG is most often ordered when symptoms do not match a total testosterone result.
SHBG in women
For women, SHBG shapes how strongly both estrogen and testosterone act. Oral estrogen raises SHBG more than estrogen through the skin, which is one reason clinicians consider the delivery route when libido or energy changes on hormone therapy. Low SHBG is common in PCOS and with insulin resistance.
Can you change it?
SHBG follows its causes. Improving insulin resistance, weight and thyroid function can shift it, and changing medications can too. Chasing the number itself is rarely the goal; it is a tool for interpreting your hormones. A HealifyMD clinician reviews SHBG alongside total testosterone, estradiol and your symptoms.
Why it matters after 45
SHBG tends to shift in midlife in both directions. Weight gain and insulin resistance pull it down, while thyroid changes, liver conditions and some medicines push it up. That is why two people with the same total testosterone can feel very different, and why your clinician may ask for SHBG before deciding a total testosterone result explains your symptoms.
SHBG: common questions
Is high SHBG bad?
Not inherently. It matters when it reduces free hormone enough to cause symptoms, or when it points to an underlying issue such as thyroid or liver disease.
Do I need SHBG if my total testosterone is normal?
It can help when you have symptoms of low testosterone despite a normal total, or when your total is borderline.
Does oral estrogen affect SHBG?
Yes. Estrogen taken by mouth tends to raise SHBG, which can lower free testosterone in women.
How is free testosterone calculated from SHBG?
Labs can estimate it with a formula using total testosterone, SHBG and albumin, or measure it directly with specialized methods.
Can weight loss change SHBG?
In people with obesity and insulin resistance, weight loss often raises SHBG toward a more typical range.
Do I need to fast for SHBG?
It is usually drawn with a morning testosterone test, which may be scheduled fasting. Follow your lab instructions.
Sources
We cite government agencies, professional societies and peer-reviewed research. See our editorial policy.
- Sex hormone-binding globulin (SHBG) blood testMedlinePlus (U.S. National Library of Medicine)
- Testosterone levels testMedlinePlus (U.S. National Library of Medicine)
- Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline (2018)Endocrine Society