- Made by
- The liver
- Binds
- Testosterone and estradiol
- Example adult range (Labcorp, men 20–49)
- 16.5–55.9 nmol/L; ranges vary by lab, sex and age
- Example adult range (Labcorp, women 20–49)
- 24.6–122.0 nmol/L
- Before the draw
- Labcorp advises stopping biotin at least 72 hours ahead
Bound, loosely bound and free
Most testosterone in your blood isn't floating freely. MedlinePlus explains that it is mostly attached to proteins, mainly SHBG and albumin. Testosterone stuck to SHBG is held tightly and is largely unavailable to tissues. Testosterone on albumin is held loosely and can be released where it is needed. A small free fraction is unattached and ready to act.
A total testosterone test counts all of it together. So if SHBG rises, total testosterone can look fine even while the usable portion shrinks. If SHBG falls, total testosterone may look low while the free fraction holds up.
Typical ranges and why they vary
Reference ranges depend on the lab and the assay. As one example, Labcorp lists about 16.5 to 55.9 nmol/L for men aged 20 to 49 and 19.3 to 76.4 nmol/L for men over 49. For women it lists about 24.6 to 122.0 nmol/L at ages 20 to 49 and 17.3 to 125.0 nmol/L after 49.
Notice that the male range shifts upward with age. SHBG tends to rise in men as they get older, which is one reason midlife men can have a respectable total testosterone with a lower free level. Always compare your result with the range on your own report.
What pushes SHBG up
- Older age in men
- Estrogen, including birth control pills and oral (swallowed) estrogen, which acts on the liver
- An overactive thyroid
- Some anti-seizure medicines
- Cirrhosis and other liver conditions
- Pregnancy
What pulls SHBG down
- Excess body weight, particularly with insulin resistance
- An underactive thyroid
- Androgens, including testosterone therapy
- Polycystic ovary syndrome (PCOS)
- Acromegaly, a rare growth hormone condition
When free testosterone is the better number
The AUA advises diagnosing low testosterone only when symptoms are present and two early-morning total testosterone results are low, with under 300 ng/dL as a reasonable cutoff. The Endocrine Society also recommends measuring free testosterone when indicated, such as when total testosterone sits near the lower limit or SHBG is likely to be abnormal.
Free testosterone can be measured directly by specialized methods or calculated from total testosterone, SHBG and albumin. Either way, it helps answer the real question: how much hormone is reaching your tissues?
SHBG for women
SHBG matters for women too. A low SHBG can mean more free testosterone, which is why it is often checked when someone has acne, unwanted hair growth or irregular periods. Labcorp notes it can be used to calculate the free androgen index for that purpose.
If you take oral estrogen, expect SHBG to rise, which can lower free testosterone. Transdermal estradiol, such as a patch or gel, has less effect on the liver. That difference is one of many factors your clinician weighs when choosing a form of hormone therapy.
Three examples of SHBG changing the picture
These simplified scenarios show why clinicians rarely read total testosterone alone. They are illustrations, not diagnoses.
A lean 61-year-old man who runs most days has a total testosterone in the low-normal range and a high SHBG. He reports low drive and poor recovery. Because so much of his testosterone is tightly bound, his calculated free testosterone may be low, which changes the conversation even though the total looked acceptable.
A 52-year-old man with central weight gain and prediabetes has a low total testosterone and a low SHBG. Some of his low total simply reflects less carrier protein, so his free testosterone may be closer to normal. Addressing weight and insulin resistance can shift both numbers, and a free testosterone result helps decide whether treatment is needed at all.
A 49-year-old woman starts oral estrogen for hot flashes and later notices lower desire. Her SHBG has risen, which can reduce free testosterone. Her clinician might discuss whether a transdermal form fits better, alongside the many non-hormonal reasons desire can change in midlife.
How HealifyMD uses SHBG
On a hormone panel, SHBG is a supporting marker. Your clinician uses it to interpret testosterone and estradiol, to decide whether a free testosterone calculation is needed and to spot clues about metabolic or thyroid health. It is not usually a treatment target by itself. Treatment decisions, such as starting testosterone therapy, follow established guidance on repeat morning tests, symptoms and safety labs like hematocrit and PSA.
Common questions
Can I lower my SHBG?
SHBG usually follows its causes. Treating an overactive thyroid or changing an oral estrogen to a transdermal one can shift it, but chasing the number itself isn't usually the goal.
Is high SHBG bad?
Not in itself. It matters because it can lower free testosterone, so a high SHBG with low-normal total testosterone and symptoms deserves a free testosterone check.
Why is my testosterone normal when I feel awful?
A high SHBG can leave less free hormone even with a normal total. Thyroid, iron, sleep apnea and mood are also common causes of similar symptoms.
Does low SHBG mean anything for my metabolism?
Low SHBG often goes along with excess weight and insulin resistance. It's a clue worth pairing with fasting glucose, A1c or fasting insulin.
Should I stop biotin before testing?
Labcorp advises stopping biotin at least 72 hours before an SHBG test, since it can interfere with the assay. Check your own lab's instructions.
Does the time of day matter?
SHBG itself is fairly stable, but testosterone is usually drawn in the morning, roughly 7 to 10 a.m., when levels are highest, so both are often collected together then.
Will testosterone therapy change my SHBG?
Androgens tend to lower SHBG. Your clinician tracks total and sometimes free testosterone during treatment rather than SHBG alone.
Sources
We cite government agencies, professional societies and peer-reviewed research. See our editorial policy.
- Testosterone Levels TestMedlinePlus (U.S. National Library of Medicine)
- Sex Hormone-binding Globulin (SHBG)Labcorp
- Testosterone Deficiency GuidelineAmerican Urological Association
- Testosterone Therapy in Men with Hypogonadism GuidelineEndocrine Society