New Biomarker Published Jun 19, 2026
SHBG (Sex Hormone-Binding Globulin)
SHBG is a liver-made blood protein that changes how much testosterone and estrogen are free to act on tissues.
Also known as
sex hormone binding globulin · sex hormone-binding globulin · SHBG test · SHBG blood test · testosterone binding globulin · TeBG · sex steroid binding globulin
Why this matters
SHBG can explain why a “normal” total testosterone result does not match how someone feels. It also moves with thyroid status, liver health, insulin resistance, oral estrogen use, pregnancy, and some medications, so it is often a clue about the setting around the hormone result, not a diagnosis by itself.
4 min read · 872 words · 3 sources
In brief
SHBG (sex hormone-binding globulin) is a liver-made blood protein that binds testosterone and estrogen, and it matters most when total hormone levels do not match symptoms or free hormone status.
- SHBG controls the free fraction of sex hormones in blood, so higher SHBG lowers free testosterone relative to total testosterone 3.
- SHBG helps interpret testosterone testing when symptoms and total testosterone results do not match 2.
- Thyroid disease, liver disease, oral estrogen, pregnancy, obesity, and insulin resistance can shift SHBG 1.
Deep dive
How it works
SHBG binds dihydrotestosterone most strongly, testosterone and estradiol with medium strength, and hormones such as DHEA and androstenedione more weakly. Because it binds and releases hormones reversibly, the SHBG level changes the balance between tightly bound hormone and hormone that can more readily reach tissues.
When you'll see this
The term in the wild
Scenario
A 42-year-old man has total testosterone of 360 ng/dL, SHBG of 82 nmol/L, and symptoms that do not match the “normal” total testosterone label.
What to notice
The SHBG value is near or above the upper end of some adult male ranges, such as 10 to 80 nmol/L. More testosterone may be tightly bound, so calculated or accurately measured free testosterone becomes the more useful next result.
Why it matters
This can prevent the common mistake of dismissing symptoms because total testosterone alone was inside the reference range.
Scenario
A 29-year-old woman being evaluated for acne and irregular cycles has SHBG of 18 nmol/L, with a lab reference range near 20 to 130 nmol/L for non-pregnant women.
What to notice
Low SHBG can fit with higher androgen effect, polycystic ovary syndrome, obesity, hypothyroidism, or insulin resistance. It does not name the cause by itself.
Why it matters
The result points the visit toward context: cycle pattern, free testosterone or free androgen index, thyroid testing, glucose or insulin markers, and medication history.
Scenario
Someone takes Nature Made Biotin 5000 mcg daily and gets an unexpectedly low SHBG result.
What to notice
5000 mcg equals 5 mg. Some SHBG tests can be affected by high-dose biotin taken close to the blood draw, and one lab warns about doses above 5 mg in the prior 12 hours.
Why it matters
Holding biotin before repeat testing, under the lab or clinician’s instructions, may prevent a false interpretation.
Scenario
A lab report lists SHBG as 115 nmol/L in a person taking an oral combined contraceptive.
What to notice
Oral estrogen exposure can raise SHBG. In this setting, the SHBG value may reflect the medication effect rather than a new disease signal.
Why it matters
Medication context keeps the result from being overread as a standalone hormone disorder.
Key takeaways
- SHBG is measured in nmol/L and typical adult reference ranges are wide, such as 10 to 80 nmol/L for men and 20 to 130 nmol/L for non-pregnant women in one lab system.
- High SHBG can make free testosterone lower than total testosterone suggests.
- Low SHBG can make total testosterone look low while free testosterone may be less reduced.
- SHBG is made mostly by the liver and is influenced by thyroid status, liver disease, oral estrogens, pregnancy, obesity, insulin resistance, and some medications.
- High-dose biotin supplements can falsely lower SHBG results in some lab methods.
The full picture
The number that can make “normal testosterone” misleading
A testosterone lab can look fine on paper while the useful part of the signal is low or high. The reason is that most sex hormone in blood is not floating around alone. Some is attached to carrier proteins. SHBG, short for sex hormone-binding globulin, is one of the main carriers. It is made mostly in the liver, circulates in blood, and binds testosterone and estradiol, a major form of estrogen.
Here is the surprise: SHBG does not measure testosterone or estrogen. It measures how tightly the bloodstream is holding onto part of those hormones. Hormone attached tightly to SHBG is less available to enter tissues. Hormone that is unattached, called free hormone, is more available. Albumin, another blood protein, also carries sex hormones, but it holds them much more loosely than SHBG.
Why the same total testosterone can mean two different things
Total testosterone counts several pools together: testosterone bound tightly to SHBG, testosterone loosely bound to albumin, and free testosterone. If SHBG is high, more testosterone may be tied up, so free testosterone can be lower than expected. If SHBG is low, total testosterone can look low even when free testosterone is less affected. This is why the Endocrine Society recommends checking free testosterone, either by a direct equilibrium dialysis method or by a reliable calculation, when total testosterone is near the lower end or when SHBG is likely to be altered.
Common adult lab ranges are broad and lab-specific. One University of Iowa laboratory lists men: 10 to 80 nmol/L and non-pregnant women: 20 to 130 nmol/L. Mayo Clinic notes that SHBG is useful in evaluating suspected androgen excess in women, infertility, puberty disorders, thyroid hormone excess, and monitoring sex-steroid or anti-androgen therapy. The key point is that SHBG is interpreted with symptoms, sex, age, menstrual or pregnancy status, medications, and related labs.
What pushes SHBG up or down
SHBG often rises with older age in men, thyroid hormone excess, liver cirrhosis, pregnancy, oral contraceptives, and some anti-seizure medicines. It often falls with obesity, hypothyroidism, polycystic ovary syndrome, high androgen states, and insulin resistance. A low SHBG result is not proof of insulin resistance, but it can fit that pattern, especially when waist gain, elevated fasting insulin, high triglycerides, or abnormal glucose results are also present.
One supplement detail matters: high-dose biotin, commonly sold for hair, skin, and nails, can interfere with some SHBG immunoassays. The University of Iowa lab warns that biotin doses above 5 mg within the prior 12 hours may falsely lower SHBG results.
The one decision to make today
If SHBG is flagged and testosterone is part of the question, do not act on total testosterone alone. The strongest next step is to review the result with a clinician using free testosterone calculated from total testosterone, SHBG, and albumin, or measured by a high-quality method when needed. That single move turns SHBG from a confusing extra number into context for the hormone result.
Myths vs reality
What people get wrong
Myth
High SHBG means the body has too much testosterone.
Reality
High SHBG can mean more testosterone is tightly bound in blood. The free amount may be normal, low, or occasionally high depending on total testosterone and albumin.
Why people believe this
Many lab portals display total testosterone and SHBG on the same screen, but they do not automatically show how binding changes free testosterone.
Myth
Low SHBG is always good because it leaves more testosterone free.
Reality
Low SHBG can come with obesity, hypothyroidism, polycystic ovary syndrome, high androgen states, or insulin resistance. It can also make total testosterone look lower than expected.
Why people believe this
Fitness and testosterone forums often frame SHBG only as something that “steals” testosterone, which ignores why the liver changed SHBG production in the first place.
Myth
An SHBG result is exact even if you take hair and nail biotin.
Reality
Some SHBG tests can read falsely low after high-dose biotin supplements, depending on the lab method.
Why people believe this
Biotin is sold as a vitamin supplement, so people often do not think of it as something that can distort lab tests. The named issue is biotin interference in immunoassays, the antibody-based tests many labs use.
How to use this knowledge
For anyone using testosterone therapy, oral contraceptives, anti-androgens, thyroid medication, or high-dose biotin, the failure mode to avoid is comparing SHBG results across time without noting medication and supplement changes. A real trend requires the same lab method when possible and a stable testing setup.
Frequently asked
Common questions