Lab Reference Library / Sex Hormone Binding Globulin
Hormones
Sex Hormone Binding Globulin
SHBGReference range, optimal functional medicine levels, and why SHBG is the critical gatekeeper that determines how much of your testosterone and estrogen is actually biologically active, and how insulin resistance, thyroid function, and liver health all drive it.
Most SearchedHormone Marker
Standard Range (M)10 to 57 nmol/L
FM Optimal (M)20 to 40 nmol/L
FM Optimal (W)40 to 80 nmol/L
Unitsnmol/L
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Category: Hormones | Also known as: Sex Hormone-Binding Globulin, Testosterone Binding Globulin | Sample: Serum (fasting preferred)
1. What This Test Measures
Sex Hormone Binding Globulin (SHBG) is a glycoprotein produced primarily by the liver that acts as a transport and regulatory protein for sex hormones in the bloodstream. It binds tightly to testosterone, dihydrotestosterone (DHT), and estradiol, in that order of binding affinity, carrying them through circulation while simultaneously preventing them from entering cells and exerting biological effects.
The key concept is hormonal bioavailability. Of the total testosterone or estradiol measured in a standard blood test, only a fraction is actually biologically active:
- SHBG-bound hormones (60 to 70%): tightly bound; completely biologically inactive
- Albumin-bound hormones (25 to 35%): loosely bound; weakly bioavailable; may dissociate in tissues
- Free hormones (1 to 4%): completely unbound; the only fraction fully able to enter cells and bind receptors
SHBG therefore functions as a hormonal dimmer switch. When SHBG is high, less hormone is available to cells regardless of total levels. When SHBG is low, more hormone is biologically active, which can be beneficial or problematic depending on context and sex.
SHBG production in the liver is exquisitely sensitive to metabolic and hormonal signals, making it one of the most clinically useful indirect markers of insulin resistance, thyroid status, and liver function available on a routine hormone panel.
2. Why This Test Matters
SHBG is essential context for any hormone evaluation. Without it, total testosterone, estradiol, and other sex hormone values can be deeply misleading:
- Free testosterone calculation: free testosterone, the clinically most relevant form, cannot be accurately assessed without knowing SHBG. A man with total testosterone of 650 ng/dL and SHBG of 70 nmol/L has significantly less free testosterone than a man with total testosterone of 450 ng/dL and SHBG of 20 nmol/L. The higher total testosterone man may be functionally hypogonadal while the lower total testosterone man is not.
- Insulin resistance surrogate: SHBG is one of the most sensitive early markers of insulin resistance available. Insulin directly suppresses hepatic SHBG production. Low SHBG is consistently associated with elevated fasting insulin, high HOMA-IR, metabolic syndrome, and type 2 diabetes risk, often before fasting glucose becomes abnormal.
- Cardiovascular risk: low SHBG is independently associated with increased cardiovascular disease risk in both men and women, beyond its association with insulin resistance and metabolic syndrome.
- PCOS diagnosis and management: low SHBG is a hallmark of PCOS. Insulin-driven SHBG suppression increases free testosterone, contributing to the androgenic symptoms of PCOS. SHBG is a critical monitoring marker for PCOS treatment response.
- Thyroid function: thyroid hormones stimulate SHBG production. Hyperthyroidism raises SHBG; hypothyroidism lowers it. Unexpectedly low SHBG can be an early sign of thyroid dysfunction.
- Hormone therapy monitoring: during testosterone replacement therapy in men, SHBG must be monitored to interpret free testosterone levels accurately and avoid over- or under-dosing.
3. Standard Lab Reference Range
| Population | Standard Range | Units |
|---|---|---|
| Men (adult) | 10 to 57 | nmol/L |
| Women (premenopausal) | 18 to 144 | nmol/L |
| Women (postmenopausal) | 17 to 125 | nmol/L |
These wide standard ranges reflect population averages and are of limited clinical utility. A man with SHBG of 55 nmol/L and a man with SHBG of 12 nmol/L are both "normal" yet have dramatically different free testosterone levels and represent entirely different hormonal and metabolic profiles. Functional medicine uses context-specific optimal targets.
4. Optimal Functional Medicine Range
| SHBG Level | Men Interpretation | Women Interpretation |
|---|---|---|
| Below 15 nmol/L | Very low; strong insulin resistance signal; excess free testosterone | Very low; PCOS and androgen excess risk; significant insulin resistance |
| 15 to 19 nmol/L | Low; metabolic dysfunction likely; evaluate insulin resistance | Low; evaluate for PCOS and insulin resistance |
| 20 to 40 nmol/L | Optimal: balanced free testosterone availability | Low-normal for women; may indicate androgen excess |
| 40 to 80 nmol/L | Elevated for men; may reduce free testosterone availability | Optimal for women: appropriate hormonal balance |
| Above 80 nmol/L (M) | High; evaluate thyroid, liver, estrogen excess; low free T likely | High-normal; interpret in clinical context |
| Above 100 nmol/L | Very high; significant reduction in free sex hormone availability | Elevated; evaluate for hyperthyroidism, eating disorder, or excess estrogen |
5. Symptoms Associated With Abnormal SHBG
Low SHBG
- In men: abdominal weight gain, fatigue, elevated triglycerides, insulin resistance signs; paradoxically normal or high total testosterone with excess free fraction
- In women: acne, hirsutism (excess facial and body hair), irregular or absent menstrual cycles, PCOS symptoms, scalp hair thinning
- Both sexes: signs of metabolic syndrome; abdominal obesity, elevated triglycerides, low HDL, hypertension
- Elevated cardiovascular risk markers
- Insulin resistance and blood sugar dysregulation symptoms
High SHBG
- In men: low libido, erectile dysfunction, fatigue, reduced muscle mass, depression, poor motivation; classic low free testosterone symptoms despite potentially "normal" total testosterone
- In women: low libido, vaginal dryness, fatigue, mood disturbances; low free estrogen and testosterone availability
- Poor response to testosterone replacement therapy if SHBG not addressed
- Signs of hyperthyroidism if thyroid-driven elevation
- Signs of liver disease or anorexia if driven by those conditions
6. What Causes Abnormal SHBG
Causes of low SHBG
- Insulin resistance and hyperinsulinemia: the most common cause; insulin directly suppresses hepatic SHBG production; low SHBG is among the earliest and most sensitive surrogate markers for insulin resistance
- Obesity: particularly visceral adiposity; adipose tissue produces inflammatory cytokines and androgens that suppress SHBG
- Type 2 diabetes
- Hypothyroidism: reduced thyroid hormone stimulation of SHBG synthesis
- Excess androgens: (testosterone, DHEA); androgens suppress SHBG production
- Anabolic steroid use: dramatically lowers SHBG
- Non-alcoholic fatty liver disease (NAFLD): impairs hepatic SHBG production
- Polycystic ovarian syndrome (PCOS): a combination of insulin resistance and androgen excess drives SHBG down
- Progestins and synthetic androgens in oral contraceptives or HRT
Causes of high SHBG
- Hyperthyroidism: thyroid hormones are the primary stimulators of hepatic SHBG production
- Aging: SHBG rises with age in men, progressively reducing free testosterone availability
- Oral estrogen therapy or high-dose oral contraceptives: first-pass liver effect dramatically raises SHBG; transdermal estrogen does not have this effect
- Liver disease (cirrhosis): paradoxically elevates SHBG through disrupted hepatic regulation
- Caloric restriction and eating disorders (anorexia): severe caloric deficit upregulates SHBG
- Vegetarian and vegan diet: high fiber intake is independently associated with higher SHBG
- Anti-epileptic drugs (phenytoin, carbamazepine): induce hepatic proteins including SHBG
7. How to Improve This Marker
To Raise Low SHBG
- Address root cause: improve insulin sensitivity (most impactful)
- Reduce refined carbohydrates and sugar
- Resistance training and weight loss
- Optimize thyroid function if hypothyroid
- Increase dietary fiber; consistently associated with higher SHBG
- Reduce alcohol intake
- Switch from oral to transdermal estrogen if oral estrogen is the driver
- Treat PCOS-related insulin resistance
To Lower High SHBG
- Treat underlying hyperthyroidism if present
- Address caloric restriction or eating disorder if contributing
- Resistance training modestly lowers SHBG in men
- Consider switching from oral to transdermal estrogen if OCP is elevating SHBG
- Evaluate and address liver disease
- If medication-induced, discuss alternatives with prescribing physician
Targeted Support
- Zinc: inhibits hepatic SHBG production; particularly relevant for men with low SHBG and excess free testosterone
- Boron: shown in clinical studies to lower SHBG and increase free testosterone; 3 to 6mg per day
- Berberine: improves insulin sensitivity, indirectly raising SHBG in low-SHBG states
- Myo-inositol: improves insulin sensitivity in PCOS; raises SHBG as insulin resistance improves
- Magnesium: improving insulin sensitivity raises SHBG in patients with low SHBG due to metabolic syndrome
- Metformin: raises SHBG in patients with insulin-driven low SHBG and PCOS
8. Related Lab Tests
SHBG is most informative when interpreted alongside these related markers:
Total TestosteroneRequired for Complete Picture
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Free TestosteroneThe Biologically Active Fraction
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Fasting InsulinPrimary Metabolic Driver of Low SHBG
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HOMA-IRInversely Correlated with SHBG
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TSHPrimary Stimulator of SHBG Production
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EstradiolEstrogen Influences SHBG and Free Hormone Balance
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9. When Testing Is Recommended
- Any patient presenting with symptoms of low testosterone despite normal total testosterone levels
- PCOS evaluation; SHBG is a core diagnostic and monitoring marker
- Men and women on hormone replacement therapy; essential for accurate free hormone calculation
- Patients with metabolic syndrome, insulin resistance, or type 2 diabetes; SHBG provides additional metabolic risk information
- Women with acne, hirsutism, or irregular cycles to assess androgen excess and free testosterone availability
- Men with fatigue, reduced libido, or muscle loss despite "normal" total testosterone
- Evaluation of thyroid function in conjunction with suspected hyperthyroidism
- Monitoring response to insulin-sensitizing therapies (metformin, lifestyle interventions)
- Any comprehensive functional medicine hormone panel
10. Clinical Perspective
Clinical Perspective
SHBG is the marker that explains why so many men come to me saying "my testosterone is fine, my doctor tested it" but they still feel terrible. Total testosterone tells you how much is in circulation. SHBG tells you how much is locked up and unavailable. I regularly see men with total testosterone of 550 to 650 ng/dL and SHBG of 60 to 70 nmol/L who calculate out to a free testosterone in the bottom quartile of normal, and they have every symptom of testosterone deficiency. Conversely, SHBG is the first marker I look at when a woman presents with acne, hair loss, and irregular cycles. In PCOS, the combination of low SHBG and insulin resistance creates a perfect storm of androgen excess that looks almost identical to the symptoms of low estrogen at first glance. You cannot do hormone medicine without knowing SHBG. It is as fundamental as the hormone itself.
Brian Lamkin, DO | Founder, The Lamkin Clinic | Edmond, Oklahoma
11. Frequently Asked Questions
What is SHBG?
SHBG (Sex Hormone Binding Globulin) is a glycoprotein produced by the liver that binds testosterone, estradiol, and DHT in the bloodstream. Only the unbound fraction of these hormones, called free hormones, can enter cells and exert biological effects. SHBG acts as a hormonal gatekeeper: high SHBG reduces free hormone availability; low SHBG increases it. It is also a sensitive surrogate marker for insulin resistance and metabolic health.
What does low SHBG mean?
Low SHBG indicates that insulin resistance, metabolic syndrome, excess androgens, hypothyroidism, or fatty liver disease is suppressing hepatic SHBG production. In men, more testosterone is free and biologically active, which paradoxically is often associated with metabolic dysfunction. In women, low SHBG increases free testosterone, contributing to PCOS symptoms including acne, hirsutism, and menstrual irregularities. Low SHBG is one of the most sensitive clinical markers for insulin resistance.
What does high SHBG mean?
High SHBG means more sex hormones are bound and unavailable to cells. In men, this is the most common cause of functional hypogonadism with normal total testosterone; high SHBG leaves too little free testosterone for cells to utilize. Common drivers include hyperthyroidism, aging, oral estrogen, liver disease, and severe caloric restriction.
How does SHBG affect testosterone?
SHBG binds testosterone tightly, rendering it biologically inactive. A man can have normal total testosterone of 600 ng/dL but very low free testosterone if SHBG is elevated. Conversely, a man with lower total testosterone of 400 ng/dL and low SHBG may have perfectly adequate free testosterone. Total testosterone without SHBG provides an incomplete and potentially misleading hormonal picture.
How do you lower SHBG naturally?
For elevated SHBG, address the underlying driver: treat hyperthyroidism if present, address caloric restriction, and consider switching from oral to transdermal estrogen if oral contraceptives are the cause. Resistance training and boron supplementation (3 to 6mg per day) modestly lower SHBG. For low SHBG, the primary intervention is improving insulin sensitivity through diet, resistance training, and weight loss.
What labs should be tested alongside SHBG?
SHBG is most informative when evaluated alongside total testosterone, free testosterone, estradiol, fasting insulin, HOMA-IR, and thyroid function (TSH, Free T3). Together these provide a complete picture of hormonal bioavailability and the metabolic and thyroid drivers of SHBG levels.
Content authored and clinically reviewed by Brian Lamkin, DO, founder of The Lamkin Clinic in Edmond, Oklahoma. Brian Lamkin, DO has 25+ years of experience in functional and regenerative medicine. This page reflects current functional medicine practice standards and is updated as new clinical evidence becomes available.
Total testosterone without SHBG is half the story.
Understanding how much hormone is actually available to your cells requires a complete hormone panel. Schedule a consultation to evaluate SHBG alongside your full hormone profile.
Schedule a ConsultationMedical Disclaimer: This content is provided for educational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Lab interpretation should always be performed in clinical context by a qualified healthcare provider. Reference ranges and optimal targets may vary based on individual patient history, clinical presentation, and laboratory methodology. Schedule a consultation to discuss your specific results with Dr. Lamkin.