SHBG – Sex Hormone-Binding Globulin Levels
Sex Hormone-Binding Globulin (SHBG) is a liver-produced protein that binds sex hormones—primarily testosterone and estradiol—regulating their bioavailability and activity in the body. Measuring SHBG levels helps interpret hormone test results, assess conditions like hypogonadism, polycystic ovary syndrome (PCOS), thyroid disorders, and metabolic disease, and guide treatment decisions. Levels can be influenced by age, sex, obesity, insulin resistance, liver function, medications, and hormonal therapies, so results are best evaluated alongside clinical context and other hormone measurements. PMID references and clinical thresholds vary, so clinicians typically combine SHBG with total and free hormone assays for accurate assessment.
SHBG Levels & Hormone Availability
Sex Hormone–Binding Globulin (SHBG), a liver-made protein that binds testosterone and estradiol, controls how much hormone is biologically available; measuring SHBG alongside total and free hormone levels improves interpretation of tests and helps diagnose and manage conditions like hypogonadism, PCOS, thyroid disease, and metabolic disorders. SHBG is affected by age, sex, body weight, insulin resistance, liver function, medications, and hormone therapy, so values should be interpreted in clinical context with complementary assays and established thresholds.
What is SHBG and Its Functions?
Sex hormone–binding globulin (SHBG) is a liver-produced glycoprotein that binds circulating sex steroids—primarily testosterone and estradiol—thereby regulating their free (biologically active) fraction, distribution, and clearance; because SHBG alters hormone bioavailability, its measurement alongside total and calculated free hormone levels improves interpretation of lab results and aids diagnosis and management of conditions such as hypogonadism, PCOS, thyroid disease, and metabolic disorders. SHBG concentrations vary with age, sex, adiposity, insulin resistance, liver function, medications, and hormonal therapies, so values must be interpreted in the context of clinical presentation and complementary hormone assays rather than in isolation.
Normal SHBG Values & Age/Sex Variations
Typical adult SHBG reference ranges vary by lab but are roughly 10–57 nmol/L in men and 18–144 nmol/L in women (with higher values in pregnancy and fluctuations across the menstrual cycle); SHBG tends to be lower with obesity, insulin resistance and androgen excess (e.g., PCOS) and higher with aging, estrogens, hyperthyroidism, liver disease recovery, and some medications, so interpretation requires age- and sex-specific reference intervals and correlation with clinical context and total/free hormone levels.
Low SHBG: Causes & Implications
Low SHBG is most often seen with obesity, insulin resistance, metabolic syndrome, type 2 diabetes, androgen excess (e.g., PCOS), and certain medications (glucocorticoids, androgens, anticonvulsants), and can also reflect hepatic dysfunction; low SHBG increases the fraction of free testosterone and estradiol, which may exacerbate androgenic symptoms, menstrual irregularities, infertility, and cardiometabolic risk, so clinicians interpret low SHBG alongside total and free hormone measurements and the clinical picture to guide management.
High SHBG: Causes, Effects & Treatment
High SHBG: Causes, Effects & Treatment — Elevated SHBG is commonly caused by factors that raise hepatic SHBG production such as aging, exogenous or endogenous estrogens, hyperthyroidism, hepatic disease or recovery, certain medications (e.g., anticonvulsants, tamoxifen), and genetic variants; it reduces the free (bioactive) fraction of testosterone and estradiol, which can lead to symptoms like low libido, fatigue, erectile dysfunction or menstrual disturbances and infertility despite normal total hormone levels. Evaluation focuses on confirming high SHBG with total and free hormone assays, screening for underlying drivers (thyroid function, liver tests, meds, estrogen exposure), and treating the cause; symptomatic men may need dose-adjusted testosterone replacement or alternative formulations, women may require tailored hormonal therapy or fertility-directed management, and reversible contributors (thyroid disease, medications, weight and metabolic factors) should be corrected.
How to interpret your results
Your SHBG result rarely stands alone. Clinicians read it next to a total testosterone value and use the pair to estimate how much testosterone is actually free and biologically available to your tissues. That step matters because total testosterone alone cannot distinguish between hormone bound to proteins (inactive) and hormone moving freely (active).
The general logic looks like this:
| Your SHBG | What it suggests about free testosterone | Common contexts |
|---|---|---|
| Below the reference range | More of your total testosterone is likely free and available | Hypothyroidism, type 2 diabetes or insulin resistance, obesity, anabolic steroid use, Cushing syndrome, PCOS in females |
| Within the reference range | Free testosterone broadly tracks total testosterone | Most healthy adults |
| Above the reference range | Less of your total testosterone is available for tissues | Liver disease, hyperthyroidism, certain eating disorders, estrogen-containing medicines in females, decreased sex hormone production in males |
A normal total testosterone value can still mask deficiency or excess once SHBG is factored in. That is why providers often pair the two tests when symptoms do not match an isolated total testosterone reading. SHBG also fluctuates throughout life in response to changing metabolic and physiologic states, and is altered by both natural hormones and synthetic steroids — so a single measurement reflects a snapshot, not a fixed trait.
If you want to revisit the broader hormone panel SHBG anchors, see our pages on total testosterone and estradiol, which cover the bound-and-free testing logic in more depth.
How to prepare for the SHBG blood test
Preparation is minimal. No special preparations are needed before an SHBG blood test. The sample itself is a routine venous draw: a clinician inserts a small needle into a vein in your arm, collects blood into a tube, and the procedure usually takes less than five minutes.
The substantive step on your end is medication disclosure. Tell your provider about every prescription drug, over-the-counter medicine, vitamin, and supplement you take, because hormone-containing products in particular can shift SHBG levels. Examples MedlinePlus flags include:
- Birth control pills
- Estrogen therapy
- Anabolic steroids
Importantly, do not stop any medication on your own before the test — discontinuation should only happen if your provider explicitly tells you to.
The risks of the draw itself are very small. You may notice slight pain or bruising at the puncture site, but most symptoms resolve quickly. If you tend to feel faint with blood draws, mention it before the needle goes in so the team can have you lie down.
SHBG and free testosterone: why both matter
The reason SHBG is ordered alongside testosterone is mechanical. Sex hormones in your blood exist in two states: bound to carrier proteins like SHBG, or unbound (free). Only the free fraction interacts with tissues to do work — supporting bone and muscle growth, reproductive function, and other roles. Hormone bound to SHBG is held out of action.
A standard total testosterone test measures both pools at once and cannot separate them. That creates a real interpretive blind spot: you can have symptoms of too little or too much free testosterone even when your total testosterone result lands inside the reference range. SHBG fills the gap by indicating which way the bound-to-free balance is tilted.
This pairing is the reason a 2012 review by Hammond frames SHBG as a tool to predict plasma free testosterone levels in patients with excess androgen exposures. The same review notes that interindividual differences in SHBG are also influenced by polymorphisms within the structural and regulatory regions of the SHBG gene, which is part of why two people with similar metabolic profiles can post different baseline SHBG values.
When the pairing changes the picture
A few clinical patterns illustrate why the pairing is informative:
- A man with borderline-low total testosterone and low SHBG may have free testosterone closer to normal than the total suggests
- A woman with hirsutism or acne and a normal total testosterone but low SHBG may still be functionally androgen-excess
- A man with a normal total testosterone but high SHBG may have functionally low free testosterone
In each case the SHBG number changes how the total testosterone number is read.
SHBG, PCOS, and women’s hormonal health
In women, SHBG measurement is most often used in the context of suspected or known polycystic ovary syndrome (PCOS) — a condition that affects the female reproductive system. An SHBG test alone cannot diagnose PCOS, but it does help providers reach a diagnosis when paired with other test results, and it is also used to monitor PCOS treatment over time.
The clinical pattern is straightforward: PCOS is associated with low SHBG, which raises the free fraction of circulating testosterone. That tilt is part of why PCOS produces androgenic symptoms in women, including:
- Excess hair growth on the face and body
- Deepening of the voice
- Irregular or absent menstrual periods
- Acne
- Weight gain
- Fertility problems
If you have these symptoms, your clinician may order an SHBG test as part of the PCOS work-up rather than as a standalone screen. The result then sits alongside total testosterone and the menstrual history.
SHBG is also relevant in pediatric medicine. Normally, SHBG levels are high in all children, and those high levels keep sex hormones from prematurely affecting body tissues. If a child’s SHBG comes back low, it can be an early signal that puberty is starting too early — a separate referral pathway that usually involves a pediatric endocrinologist.
SHBG as a metabolic risk biomarker
One of the more interesting modern uses of SHBG is as a window onto metabolic health. The 2012 Hammond review concludes that SHBG measurements, beyond their role in androgen-excess assessment, have broader utility in assessing the risk for endocrine diseases and clinical sequelae of the metabolic syndrome — namely, type 2 diabetes and cardiovascular disease.
The MedlinePlus interpretation section reflects the same pattern from the clinical side: low SHBG is associated with type 2 diabetes or insulin resistance, with obesity, and with hypothyroidism. Cushing syndrome and PCOS — both of which carry their own metabolic risks — also appear in the low-SHBG list. Conversely, elevated SHBG can reflect liver disease or hyperthyroidism.
Why metabolism affects SHBG
Hammond’s review notes that plasma SHBG levels fluctuate throughout life in response to changes in metabolic and physiologic states, and are altered by both natural hormones and synthetic steroids. That sensitivity is what turns SHBG into a useful indirect signal: a chronically low SHBG value, especially in the absence of androgen excess or anabolic steroid use, can prompt a clinician to look more closely at insulin resistance and weight-related drivers.
The review also flags an open question: it is not yet resolved whether SHBG is simply a biomarker of these diseases or actually participates in their cause — new genetic and functional data are anticipated to clarify that. Either way, the clinical association is real enough to act on.
Medications and lifestyle factors that affect SHBG
A number of medications and physiologic states shift SHBG. Knowing which apply to you helps you and your clinician interpret the number rather than treating a borderline result as a fixed trait.
Factors associated with lower SHBG:
- Hypothyroidism (underactive thyroid)
- Type 2 diabetes or insulin resistance
- Obesity
- Overuse of steroid medicines and anabolic steroids
- Cushing syndrome
- PCOS in females
- Older age (a normal physiologic decline as sex hormone production decreases)
Factors associated with higher SHBG:
- Liver disease
- Hyperthyroidism (overactive thyroid)
- Certain eating disorders
- Estrogen-containing medicines in females, including hormone replacement therapy and birth control pills
- Decreased sex hormone production in males
Two caveats follow. First, several entries are conditions you would not self-diagnose from an SHBG result alone — thyroid function tests, liver tests, and a clinical history all play a role. Our pages on TSH and fasting insulin cover two of the most common companion tests when SHBG is unexpectedly low or high.
Second, the cached evidence does not support specific protocols claiming to “lower” or “raise” SHBG with supplements, foods, or particular drug doses. Hammond’s review describes SHBG as altered by natural hormones, synthetic steroids, and metabolic state, but it does not endorse self-directed optimization. If your SHBG is out of range and bothering you, address the underlying driver with your clinician rather than chasing the number directly.
Frequently asked questions
What does it mean if my SHBG is high?
A high SHBG result usually means less of your total testosterone is available for your tissues to use, so they may not be getting enough testosterone. High SHBG can be related to liver disease, hyperthyroidism, certain eating disorders, estrogen-containing medications in females, or decreased sex hormone production in males.
What are the symptoms of low SHBG?
Low SHBG itself does not cause distinctive symptoms. Instead, it raises the free fraction of testosterone, which can amplify symptoms tied to the underlying cause — for example, hirsutism, acne, or menstrual irregularity in women with PCOS, or symptoms tied to insulin resistance, obesity, or hypothyroidism.
What is a good SHBG score?
There is no single universal “good” number. Your SHBG result should be compared against the reference range printed on your own report and read alongside your total testosterone result, since the pairing tells your provider whether free testosterone is adequate, low, or high.
What causes high SHBG?
The most commonly cited drivers of high SHBG are liver disease, hyperthyroidism, certain eating disorders, and estrogen-containing medications in females (such as hormone replacement therapy or birth control pills). Decreased sex hormone production in males is also associated with elevated SHBG.
How is SHBG different from a total testosterone test?
A total testosterone test measures all the testosterone in your blood, including hormone bound to proteins like SHBG and the small free fraction; it cannot distinguish between the two. SHBG indicates how much of that total is likely sequestered, which lets your provider estimate the active free portion.
Do I need to fast for an SHBG blood test?
No. MedlinePlus states you do not need any special preparations for an SHBG test. The one important step is to tell your provider about every medicine, vitamin, and supplement you take, because hormone-containing products can shift the result.
Can SHBG levels change over time?
Yes. The Hammond review notes that plasma SHBG levels fluctuate throughout life in response to changes in metabolic and physiologic states, and are altered by natural hormones and synthetic steroids. Genetic variation in the SHBG gene also drives interindividual differences in baseline levels.
When to talk to your doctor
SHBG is almost always interpreted in a clinical conversation rather than as a standalone alert. Speak with a provider about ordering — or revisiting — an SHBG test in the following situations:
- Men with symptoms of low testosterone (low sex drive, difficulty getting an erection, fatigue or loss of muscle mass, or fertility problems), especially when a previous total testosterone test did not explain the symptoms
- Women with symptoms of high testosterone, including excess hair growth on the face and body, deepening of the voice, irregular or absent menstrual periods, acne, weight gain, or fertility problems
- Anyone undergoing hormone replacement therapy or treatment for a hormone disorder, where SHBG can help track how the therapy is shifting hormone availability
- Women with signs of PCOS, such as irregular menstrual periods, where SHBG can support a diagnosis when paired with other tests
- Children with signs of early puberty, since low SHBG in a child can be an early signal of precocious puberty
- Anyone with an SHBG result outside the reference range who has not had it explained, since interpretation depends on the accompanying total testosterone, the clinical picture, and other tests your provider may order
If you have questions about your specific result, MedlinePlus’s plain advice still holds: talk with your provider. They can integrate the SHBG number with your symptoms, your other lab work, and any medications you take into a coherent interpretation that a single value on a printout cannot give you.
References
- MedlinePlus (U.S. National Library of Medicine, NIH)
- PubMed (U.S. National Library of Medicine, NIH)