What the SHBG test shows
Sex hormone-binding globulin (SHBG) is a protein made mainly by the liver that binds the sex hormones travelling in your blood — chiefly testosterone and estradiol — and holds them in an inactive form. Only the small unbound (free) fraction can enter cells and act, so SHBG works like a dimmer switch on how much of your sex hormones are actually available, as MedlinePlus explains.
That is what sets it apart from the hormone tests it accompanies. Total testosterone measures everything — bound plus free — while free testosterone measures only the active slice. Because most testosterone travels bound to proteins — much of it locked to SHBG — and only about 1–2% circulates free, per StatPearls, the total figure can mislead when SHBG is unusually high or low. SHBG is the number that explains the gap: labs combine it with total testosterone and albumin to report calculated free testosterone, or divide total testosterone by SHBG to give the free androgen index.
SHBG normal range
SHBG is reported in nmol/L in both the conventional (US) and SI (European) systems, so a report reads the same number on either side of the Atlantic — there is no separate unit to convert. Typical adult orientation ranges:
| Group | Orientation, nmol/L (SI identical) |
|---|---|
| Men (adult) | ~10–55 |
| Women (adult, non-pregnant) | ~20–130 |
| Pregnancy | several-fold higher (estrogen-driven) |
| Children, before puberty | high, then fall after puberty |
Two patterns matter. SHBG drifts upward with age in men even as testosterone falls, so an “in-range” number in an older man can still leave free testosterone low; and in women, oral estrogen (contraceptive pills or oral HRT) and pregnancy push SHBG well above the non-pregnant band. Ranges depend on the lab, assay, sex and age, so read your result against your own report’s range, not a general table.
Why SHBG is low
A low SHBG is the more common direction and often the more telling one, because the hormone that lowers it — insulin — also drives metabolic disease. Ordered roughly by frequency:
- Insulin resistance, obesity and type 2 diabetes (commonest). Insulin suppresses the liver’s output of SHBG, so a low value is a recognised early flag for metabolic syndrome; a large NEJM study found low SHBG strongly predicts future type 2 diabetes in both sexes.
- Polycystic ovary syndrome (PCOS). A low SHBG frees up more androgen, feeding the acne, unwanted hair growth and irregular cycles of PCOS — which is why it is central to that work-up.
- Non-alcoholic fatty liver disease, which travels with insulin resistance.
- Underactive thyroid (hypothyroidism), since thyroid hormone normally lifts SHBG.
- Androgen excess, including anabolic-steroid use, plus some progestins and corticosteroids.
- Cushing’s syndrome and acromegaly (less common), reflecting glucocorticoid and growth-hormone excess.
When is it urgent? Never in itself, but it flags metabolic risk that deserves timely attention — weight, blood pressure, HbA1c and lipids. In a woman with rapidly worsening hair growth, a deepening voice or other virilisation, a same-month endocrine review is sensible.
Why SHBG is high
A high SHBG means more testosterone is bound and less is free, so it can produce symptoms of low testosterone even when the total looks normal — the scenario the Endocrine Society flags as a reason to measure free testosterone, not just the total. Roughly by frequency:
- Overactive thyroid (hyperthyroidism), a potent driver of SHBG production.
- High-estrogen states: oral estrogen (the pill, oral HRT, tamoxifen) and pregnancy.
- Aging in men — the steady age-related climb noted above.
- Liver disease (including cirrhosis) and low body weight, such as anorexia or prolonged fasting.
- Some medications, such as certain anticonvulsants.
When is it urgent? The number itself is not an emergency, but the cause can be: a high SHBG with weight loss, palpitations, tremor or heat intolerance suggests an overactive thyroid, which needs prompt assessment.
What to test alongside
SHBG is almost never read alone — its job is to reinterpret other hormones:
- Testosterone (total) — the value SHBG exists to put in context.
- Free testosterone — the active fraction, often calculated from total testosterone and SHBG.
- Estradiol — the other main hormone SHBG binds; high-estrogen states raise it.
- LH and FSH — the pituitary signals that separate gonadal from pituitary causes of low testosterone.
- DHEAS, 17-OH-progesterone and AMH — the hyperandrogenism and PCOS work-up in women with unwanted hair growth or irregular cycles.
- Prolactin — part of the low-libido and hypogonadism work-up.
- TSH and free T4 — thyroid activity moves SHBG up or down.
- HbA1c and glucose — insulin resistance is the leading reason SHBG runs low.
- ALT — a liver check, since the liver makes SHBG and fatty liver lowers it.
What to do about an abnormal result
- Don’t self-treat, and don’t read SHBG in isolation. The number only makes sense next to your total testosterone, your symptoms and, where relevant, thyroid and metabolic markers.
- Confirm the calculated free testosterone or free androgen index. These translate an abnormal SHBG into the figure that actually matters: how much active hormone reaches your tissues.
- For a low SHBG: treat it as a prompt to check metabolic health — weight, HbA1c, blood pressure and lipids — with your primary-care doctor. The main lever is improving insulin sensitivity through weight loss and activity; there is no pill that simply “raises SHBG.”
- For a high SHBG: the first steps are a thyroid panel and a review of any oral estrogen or other medication. Persistent low free testosterone with symptoms warrants fuller hormone testing.
- See your GP or primary-care physician first; they decide whether the picture calls for an endocrinologist (hormone or thyroid disorders) or a gynecologist (PCOS or menstrual concerns).
Mini-FAQ
What does an SHBG test tell you that a testosterone test alone can’t?
It shows how much of your testosterone is bound and inactive versus free and usable. A normal total testosterone can still mean low active testosterone if SHBG is high, so labs combine the two to calculate free testosterone or the free androgen index.
What makes SHBG low?
Most often insulin resistance, obesity, type 2 diabetes, polycystic ovary syndrome (PCOS) and an underactive thyroid. A low SHBG is a recognised early signal of metabolic risk and, in women, drives up free androgens.
Does a high SHBG mean my testosterone is low?
Not always, but a high SHBG binds more testosterone and leaves less free and active. It is common with an overactive thyroid, oral estrogen such as the pill or HRT, liver disease, aging and pregnancy.
Can I change my SHBG level?
Indirectly, yes. Losing excess weight and improving insulin sensitivity tend to raise a low SHBG, while treating thyroid disease or reviewing oral estrogen can lower a high one. Do not self-medicate — SHBG is only interpreted alongside your hormones and symptoms.
Is SHBG the same as free testosterone?
No. SHBG is the carrier protein; free testosterone is the small fraction not attached to it. They tend to move in opposite directions — as SHBG rises, free testosterone falls.
