⚠ Educational only. LabPlain does not provide medical advice or diagnosis. Always discuss your specific results with your healthcare provider.
What this test measures
SHBG stands for Sex Hormone-Binding Globulin. It is a specialized protein produced primarily by your liver. Its primary job is to bind to specific sex hormones—most notably testosterone, dihydrotestosterone (DHT), and estrogen—and carry them safely through your bloodstream.
Think of SHBG as a vehicle that locks up hormones while transporting them. When a hormone is bound to SHBG, it is temporarily inactive, meaning your body's tissues and cells cannot actively use it. Only the tiny fraction of hormones that float completely free (unbound) are immediately bioavailable to regulate your energy, muscle mass, mood, and reproductive health.
Doctors typically order an SHBG test alongside total testosterone measurements. This helps evaluate whether your body has the right amount of active, usable hormones, which is often crucial when investigating symptoms of hormonal imbalances or fertility issues.
Normal reference range
Adult Men: 10–57 nmol/L | Adult Women (Non-Pregnant): 18–144 nmol/L
SHBG levels inherently differ by biological sex and change significantly with age. For instance, adult men typically possess lower baseline SHBG values than women, but a man's levels often rise gradually over time as natural testosterone drops.
Because reference thresholds fluctuate significantly between different clinical testing facilities, you should always check the exact custom range printed directly on your laboratory report.
⚖️ The Hormone Balance Connection
Because SHBG controls the balance between "bound" and "free" testosterone, looking at total testosterone alone can sometimes be misleading. An SHBG test helps your doctor calculate your Free Androgen Index (FAI) or calculated free testosterone to see the true clinical picture.
What your result might indicate
↑ If High
Elevated SHBG can imply that too much of your total testosterone or estrogen is locked up, leaving less free hormone available for your tissues. This is often seen in conditions like hyperthyroidism, liver disease, or with estrogen therapy.
↓ If Low
Lowered SHBG can indicate that less protein is binding to your sex hormones, meaning you might have a higher proportion of free, active testosterone circulating. This is often associated with insulin resistance, metabolic syndrome, or PCOS.
Symptoms associated with abnormal SHBG
↑ High SHBG Symptoms
Low libido or reduced sex drive
Chronic fatigue and low energy
Loss of muscle mass or tone
Difficulty burning fat or weight gain
Mood changes or mild depression
Erectile dysfunction (in men)
↓ Low SHBG Symptoms
Severe acne or oily skin
Excessive body or facial hair growth
Irregular or missed menstrual cycles
Unexplained weight gain around abdomen
Thinning hair on the scalp
Fertility or ovulation difficulties
Common causes of abnormal SHBG
What can raise SHBG?
An elevated SHBG level can occur when the liver produces too much of this binding protein. Common underlying factors include hyperthyroidism (an overactive thyroid), underlying liver conditions such as cirrhosis or hepatitis, and nutritional habits like prolonged fasting or severe calorie restriction.
Hormonal factors can also heavily drive up SHBG. Pregnancy naturally triggers a steep increase in this protein, as does the use of oral contraceptives or hormone replacement therapies containing oral estrogens. Additionally, as men age, their SHBG levels frequently shift upward naturally.
What can lower SHBG?
Low SHBG is very frequently tied to metabolic factors. Conditions that involve insulin resistance—such as obesity, metabolic syndrome, and poorly controlled type 2 diabetes—can signal the liver to decrease its production of SHBG. Polycystic Ovary Syndrome (PCOS) in women is also a primary cause of low SHBG levels.
Other clinical causes can include hypothyroidism (an underactive thyroid), high levels of circulating androgens (such as from anabolic steroid use), or a growth hormone deficiency. Certain medications, particularly progestins or glucocorticoids, may also drag SHBG levels down.
Tests often ordered alongside SHBG
An isolated SHBG test rarely reveals the entire clinical status. Your medical professional may also request:
Total Testosterone — measures the complete pool of testosterone (both bound and unbound)
Free Testosterone — checks the active portion of testosterone not bound to SHBG
Albumin — another abundant carrier protein that weakly binds to sex hormones
Thyroid Panel (TSH, Free T4) — screens for underlying thyroid dysfunctions affecting the liver
Fasting Glucose & Insulin — evaluates if metabolic shifts or insulin resistance are altering your protein levels
What to do next
A single out-of-range SHBG result does not establish an absolute medical diagnosis. Because SHBG serves as a regulator that reacts to a wide web of lifestyle, dietary, metabolic, and liver factors, your result must be reviewed holistically. Your practitioner will compare your SHBG level alongside free hormone scores, your comprehensive medical history, and any clinical symptoms to map out an accurate health profile.
Questions to ask your doctor
01Does my SHBG level explain why my free testosterone might differ from my total testosterone?
02Could metabolic health factors, like insulin levels or body weight, be influencing my result?
03Do my symptoms lean toward an excess of active hormones, or a deficiency?
04Are any current supplements or prescription medications I take modifying my liver's SHBG output?
05Would evaluating my thyroid performance or liver function be a reasonable next step?
06Do I need a formal referral to an endocrinologist for specialized hormone mapping?
Frequently asked questions
Can a specific diet or lifestyle choice modify my SHBG levels?
Yes, metabolic shifts significantly affect SHBG. Diets high in refined sugars that spike insulin can reduce liver SHBG production over time, while regular aerobic exercise and managing body weight can help raise low SHBG levels naturally. However, lifestyle changes should complement medical guidance for underlying conditions.
Can biotin supplements interfere with an SHBG blood draw?
Yes. Many modern hormone lab tests utilize immunoassays that can be skewed by high doses of biotin (Vitamin B7). It is often recommended to avoid high-dose biotin supplements for at least 8 to 72 hours prior to your blood draw, depending on the dose. Always consult your doctor or the testing lab.
Why do men have lower SHBG levels than women on average?
Biological differences in baseline hormone concentrations drive this variation. Higher levels of androgens (like testosterone) naturally suppress liver production of SHBG, keeping baseline values lower in men, whereas higher levels of estrogens stimulate the liver to release more SHBG.
What is the Free Androgen Index (FAI)?
The FAI is a mathematical calculation that divides your total testosterone level by your SHBG level and multiplies it by 100. It is often used by clinicians to approximate the amount of active, free testosterone in women, particularly when evaluating potential conditions like PCOS.