What is sex hormone binding globulin? How SHBG levels shape testosterone in men

Sex hormone binding globulin is a liver made protein that binds testosterone and other sex hormones, and SHBG levels help predict how much testosterone is actually available to your tissues. If you have low testosterone symptoms but “normal” total testosterone, SHBG is often the missing piece that explains why you still feel off.

Key takeaways

• In adult men, many labs list normal SHBG levels at roughly 13.3 to 89.5 nmol/L, but ranges vary by assay and lab.
• According to research in Endocrine Reviews, about 70 percent of circulating testosterone is typically bound to SHBG and is not readily usable by tissues.^[2]
• Low SHBG levels are strongly linked to insulin resistance, obesity, metabolic syndrome, and nonalcoholic fatty liver disease (NAFLD) in men.^[3]
• High SHBG levels are linked to conditions such as hyperthyroidism, liver damage, and growth hormone deficiency, so out of range results warrant a medical workup.^[4],
• Guidelines diagnose testosterone deficiency based on symptoms plus consistently low testosterone (for example, the AUA uses total testosterone <300 ng/dL as a reasonable cutoff). Treatment benefit tends to be clearer at lower baseline testosterone, while “free testosterone” cutoffs depend on the assay or calculation method and the lab’s reference ranges, especially when SHBG is abnormal.^[8]

Why SHBG levels matter for men

In practical terms, sex hormone binding globulin is a transport protein that can “hold” testosterone in your bloodstream, which changes how much testosterone your tissues can use.^[1] That is why SHBG levels can matter as much as total testosterone, especially when symptoms and lab numbers do not match.

According to research in Endocrine Reviews, testosterone in blood exists in different “pools.” Some is free, meaning it is not attached to other proteins. Some is loosely attached to albumin, a common blood protein made by the liver. And a large share is bound tightly to SHBG.^[2] From a men’s health standpoint, the free and albumin bound portions are often grouped as bioavailable testosterone, meaning testosterone your tissues can access more easily.

This is where SHBG testing becomes useful. Two men can share the same total testosterone, but if one man has high SHBG levels, he may have lower free testosterone and more symptoms. The opposite can also happen. Low SHBG levels can make free testosterone look higher, but can also signal metabolic issues that deserve attention.

How SHBG controls testosterone availability

What is sex hormone binding globulin, in plain biology

According to a 2011 review in Biology of Reproduction, SHBG is a protein produced mainly in the liver that binds sex hormones, including testosterone, dihydrotestosterone, and estradiol, and carries them through the bloodstream.^[1] Dihydrotestosterone, also called DHT, is a more potent form of testosterone created in some tissues. Estradiol is the main estrogen in men and is largely produced by converting testosterone into estradiol in body fat and other tissues.

SHBG matters because hormones bound tightly to it are less available to enter cells. In other words, SHBG acts like a regulator knob that can raise or lower the amount of “usable” hormone without changing how much hormone your body produces overall.

Free testosterone vs total testosterone, and where SHBG fits

Free testosterone is testosterone circulating without being attached to proteins. Total testosterone is the sum of free testosterone plus protein bound testosterone. According to a 2017 review in Endocrine Reviews, most testosterone in circulation, often around 70 percent, is bound to SHBG, with smaller fractions bound to albumin or circulating freely.^[2]

This is why SHBG levels can change the story. If SHBG is high, a larger fraction of testosterone is locked up. You can have a normal total testosterone on paper and still have a low free testosterone that lines up with fatigue, low libido, and reduced performance in the gym. If SHBG is low, a larger fraction is accessible, but the low SHBG itself can be a red flag for metabolic health.

Bioavailable testosterone is a practical term used in clinics. It refers to free testosterone plus albumin bound testosterone, because albumin binding is looser than SHBG binding. That is the portion more likely to reach tissues efficiently.

Why SHBG levels change over time

SHBG levels are not fixed. They can shift with age, body composition, and underlying disease. The liver is the main production site, so anything that changes liver function or liver signaling can change SHBG output.^[1]

Research published in Clinical Endocrinology links insulin resistance to reduced SHBG production.^[3] Insulin resistance is when your cells respond poorly to insulin, so your body makes more insulin to compensate. High insulin levels appear to suppress SHBG production in the liver. This helps explain why low SHBG levels often travel with weight gain and metabolic problems in men.

A 2009 study in Molecular Endocrinology found that thyroid hormones can increase SHBG production through liver signaling pathways.^[4] That is one reason hyperthyroidism, meaning an overactive thyroid, is associated with higher SHBG levels in men.

How to interpret labs when SHBG is high or low

An SHBG blood test is rarely useful in isolation. It is most informative alongside total testosterone and free testosterone. Many clinicians also check albumin, since albumin influences calculated free testosterone.

If you want your labs to map to your real life symptoms, timing matters. According to the American Urological Association, testosterone deficiency evaluation should be based on symptoms plus appropriately collected testosterone testing, and results should be confirmed rather than acted on from a single reading.^[8] In practice, you and your clinician are trying to answer two questions: is testosterone low, and if so, is it low because production is low, or because binding is high.

Here is a clinically useful way to frame it when you are reviewing SHBG levels with your doctor:

• Normal total testosterone plus high SHBG: free testosterone may be low. Symptoms may still be real and explainable.
• Low total testosterone plus low SHBG: free testosterone might be “less low” than expected, but low SHBG can point toward insulin resistance, fatty liver, or other metabolic risk.
• Normal total testosterone plus low SHBG: free testosterone can be higher, but that does not automatically mean “optimal.” Balance matters.

Evidence reviews suggest symptom improvement with testosterone focused therapy is most consistent when baseline testosterone is clearly low, and most guidelines emphasize symptoms plus repeat morning testing rather than a single number.^[8] Free testosterone can be especially helpful when SHBG is abnormal, but it should be interpreted using the assay or calculation method and the lab’s reference ranges, since “cutoffs” are not universal.

SHBG also binds DHT and estradiol in men

SHBG binds multiple sex hormones, including testosterone, DHT, and estradiol.^[1] Even though testosterone is usually the main focus in men, it helps to remember that DHT and estradiol are also part of male sexual function, body composition, and mood.

Research in Endocrinology has explored how SHBG can influence hormone action in prostate cancer cells, which is one reason abnormal SHBG levels are sometimes treated as a clue, not just a number.^[5] This does not mean SHBG causes prostate cancer. It means SHBG can be part of the broader hormone environment that your clinician may consider when evaluating risk and symptoms.

Health conditions tied to high and low SHBG

Abnormal SHBG levels can be a consequence of lifestyle, a sign of an underlying medical condition, or both. The goal is not to “treat the SHBG number.” The goal is to find out why your body is producing too little or too much SHBG, and how that is affecting free testosterone.

Conditions linked to low SHBG levels in men

• Insulin resistance: Research published in Clinical Endocrinology links insulin resistance with lower SHBG production in the liver.^[3]
• Obesity and metabolic syndrome: Metabolic syndrome is a cluster of risk factors, such as abdominal obesity and abnormal blood sugar, that raises cardiovascular risk. These metabolic patterns commonly track with low SHBG.
• Nonalcoholic fatty liver disease (NAFLD): A 2017 study in Endocrine found low SHBG levels were associated with insulin resistance in men with NAFLD.
• Hypothyroidism: Hypothyroidism is an underactive thyroid. It is linked clinically with lower SHBG in men, consistent with thyroid hormone signaling’s role in SHBG production.^[4]
• Other medical causes: Cushing syndrome, meaning chronic high cortisol, and certain cancers are also reported associations in clinical settings.

Conditions linked to high SHBG levels in men

• Hyperthyroidism: Hyperthyroidism is an overactive thyroid. A 2009 Molecular Endocrinology study supports that higher thyroid hormone signaling can increase SHBG production.^[4]
• Liver damage or chronic liver disease: Cirrhosis is advanced scarring of the liver. Hepatitis is inflammation of the liver. A 2015 study in Clinical Endocrinology described clinically meaningful testosterone abnormalities in men with advanced liver disease, where SHBG can be part of the pattern.
• Growth hormone deficiency: Growth hormone deficiency is insufficient production of growth hormone from the pituitary gland. A study in Clinical Endocrinology reported altered sex steroid patterns in men with lifetime isolated growth hormone deficiency, including SHBG changes.
• Viral infections and cancer signals: Viral infections including HIV and prostate cancer have been linked with high SHBG in clinical research and practice, though causality is complex.

Limitations: Many SHBG associations are observational, meaning they show correlation, not direct cause and effect. Your personal result still needs to be interpreted alongside symptoms, thyroid labs, liver labs, glucose markers, and testosterone fractions.

Signs your SHBG and testosterone may be out of sync

Most men do not feel “high SHBG” or “low SHBG” directly. You feel the downstream effect, usually a mismatch between your hormones and what your tissues can use. Consider talking with a clinician if you have symptoms plus abnormal SHBG levels, or symptoms that persist even with a normal total testosterone result.

• Low libido or reduced sexual interest
• Erections that are less reliable
• Low energy that does not improve with sleep
• Low mood, irritability, or reduced motivation
• Difficulty gaining muscle or recovering from training
• Brain fog or trouble concentrating
• Unexpected changes in body fat
• Symptoms that do not match total testosterone such as “normal” total testosterone but classic low testosterone complaints

Also watch for “context clues” that point toward root causes of abnormal SHBG levels. For example, increasing waist size, higher fasting glucose, or fatty liver history can point toward low SHBG driven by metabolic stress. Unexplained weight loss, palpitations, or heat intolerance can raise suspicion for hyperthyroidism, which can push SHBG up.

What to do about abnormal SHBG levels

There is no one size fits all fix for abnormal SHBG levels. The best plan depends on whether SHBG is high or low, what your free testosterone looks like, and what is driving the change. Your goal is to restore healthy hormone availability and address the underlying health issue, not chase a single lab number.

1. Step 1: Get the right tests, not just total testosterone Ask for a hormone evaluation that includes total testosterone, free testosterone (measured or calculated), SHBG, and albumin. Many clinicians also add luteinizing hormone, called LH, which is the pituitary signal that tells the testes to produce testosterone. Do not ignore metabolic markers. Fasting glucose, A1C, lipids, and liver enzymes matter because low SHBG levels are often a metabolic signal.^[3] Ask your clinician about comprehensive testing and appropriate follow up so results are interpreted in context, not as isolated numbers.
2. Step 2: Address the driver, then adjust hormones if symptoms persist If low SHBG levels are paired with metabolic risk, prioritize basics that move insulin sensitivity in the right direction. According to a 2008 study in the Journal of Applied Physiology, exercise can change sex hormone patterns in men, including factors tied to testosterone balance.^[6] A 2003 study in Obesity Research found that weight loss in obese men was associated with changes in sex hormones and sexual function, supporting that body composition can shift the hormone environment.^[7] If SHBG is high, ask your clinician about thyroid testing and liver evaluation, since those are common medical drivers in men.^[4] If you have persistent symptoms of testosterone deficiency, treatment decisions should be guided by symptoms plus repeat morning testosterone testing (total and, when appropriate, free), not total testosterone alone.^[8] Depending on the diagnosis (primary vs secondary hypogonadism), fertility goals, and risk profile, options may include treating underlying conditions, medications used off label to stimulate endogenous testosterone production, or testosterone replacement therapy with appropriate monitoring and shared decision making.
3. Step 3: Recheck and calibrate SHBG is dynamic, so you need follow up labs after meaningful changes. Recheck SHBG, total testosterone, and free testosterone, along with the metabolic markers that likely drove the change. If you start medication, monitoring is not optional. It is how you avoid overcorrecting and how you keep symptoms, safety markers, and goals aligned over time.

Myth vs fact

Use the myths below as a checklist for smarter testing, not as a diagnosis. If symptoms suggest testosterone deficiency, most guidelines recommend repeat morning testing and interpreting results in context, including SHBG when there is a mismatch between symptoms and total testosterone.^[8] That approach helps avoid overreacting to a single lab value and reduces the chance that high or low SHBG is masking what is happening with free or bioavailable testosterone.

In real life, the decision point is usually not “Is SHBG high or low?” but “Why is SHBG high or low, and what does that do to the testosterone my tissues can actually use?” For many men, the most impactful next steps are addressing metabolic health (when SHBG is low) or evaluating thyroid and liver health (when SHBG is high), then revisiting hormone levels and symptoms after those drivers are treated.

• Myth: “If my total testosterone is normal, my hormones cannot be the problem.”
  Fact: High SHBG levels can reduce free testosterone enough to cause symptoms even when total testosterone looks normal.^[2]
• Myth: “Low SHBG is always good because it means more free testosterone.”
  Fact: Low SHBG levels often track with insulin resistance and NAFLD risk in men, so it can be a health warning sign.^[3]
• Myth: “You should try to raise or lower SHBG with supplements first.”
  Fact: The most reliable levers are identifying the underlying cause, improving metabolic health, and treating thyroid or liver disease when present.^[4]
• Myth: “SHBG is just a ‘binding protein’ that does not matter clinically.”
  Fact: SHBG is a major determinant of how much testosterone is available to tissues, and it can explain symptom and lab mismatches.^[1],[2]

Practical safety note: Some medications can influence SHBG levels, but changing prescriptions to “move SHBG” is not a do it yourself project. Work with a clinician who can assess risks, benefits, and the real goal, which is symptom relief with long term safety.

Bottom line

Sex hormone binding globulin (SHBG) is a liver made protein that binds testosterone in the bloodstream. When SHBG is high, free and bioavailable testosterone can be lower even if total testosterone looks normal; when SHBG is low, free testosterone can appear higher while metabolic risk may be higher. Testing SHBG helps explain why symptoms and total testosterone do not always match.

References

1. Hammond GL. Diverse roles for sex hormone-binding globulin in reproduction. Biology of reproduction. 2011;85:431-41. PMID: 21613632
2. Goldman AL, Bhasin S, Wu FCW, et al. A Reappraisal of Testosterone’s Binding in Circulation: Physiological and Clinical Implications. Endocrine reviews. 2017;38:302-324. PMID: 28673039
3. Wallace IR, McKinley MC, Bell PM, et al. Sex hormone binding globulin and insulin resistance. Clinical endocrinology. 2013;78:321-9. PMID: 23121642
4. Selva DM, Hammond GL. Thyroid hormones act indirectly to increase sex hormone-binding globulin production by liver via hepatocyte nuclear factor-4alpha. Journal of molecular endocrinology. 2009;43:19-27. PMID: 19336534
5. Li H, Pham T, McWhinney BC, et al. Sex Hormone Binding Globulin Modifies Testosterone Action and Metabolism in Prostate Cancer Cells. International journal of endocrinology. 2016;2016:6437585. PMID: 27990161
6. Hawkins VN, Foster-Schubert K, Chubak J, et al. Effect of exercise on serum sex hormones in men: a 12-month randomized clinical trial. Medicine and science in sports and exercise. 2008;40:223-33. PMID: 18202581
7. Kaukua J, Pekkarinen T, Sane T, et al. Sex hormones and sexual function in obese men losing weight. Obesity research. 2003;11:689-94. PMID: 12805389
8. Mulhall JP, Trost LW, Brannigan RE, et al. Evaluation and Management of Testosterone Deficiency: AUA Guideline. The Journal of urology. 2018;200:423-432. PMID: 29601923