Sex Hormone Binding Globulin (SHBG)

SHBG at a glance

What is sex hormone binding globulin?

Sex hormone binding globulin is a protein, not a hormone, and the liver produces it continuously and releases it into the blood. Its job is to bind tightly to certain sex hormones and hold onto them as they travel, which sounds unremarkable until you realise what it means in practice: a hormone that is bound is a hormone that is switched off. A total testosterone or oestradiol result shows how much hormone is in circulation. The SHBG result shows how much of it the body can actually reach.

This is why SHBG appears on so many hormone panels alongside Testosterone (total) and Oestradiol (Oestrogen). On its own, it is a single number. Read next to the sex hormones it travels with, it explains a great deal about how someone feels day to day.

What does SHBG do?

The bloodstream works something like a delivery network. Testosterone and oestradiol are the parcels, and SHBG is the courier that keeps them sealed. About 60% of the testosterone in a typical man’s blood is locked to SHBG, roughly another 38% is held loosely by Albumin, and only 1 to 2% floats completely free. Albumin lets go easily, so the loosely held portion plus the free portion is described as bioavailable, meaning it is the part that can genuinely get to work in muscle, brain, skin and bone.

Only the hormone that SHBG is not holding onto can reach your cells. Illustrative proportions for testosterone in the blood.

When SHBG rises, the locked-away share grows and the usable share shrinks, even though the total hormone level has not moved at all. When SHBG falls, the opposite happens and more hormones are left free and active. Neither direction is automatically good or bad, and that nuance is the thing most people miss when a result is flagged outside the range.

Which hormones does SHBG bind?

SHBG has a strong preference for androgens. It binds dihydrotestosterone (DHT) most tightly of all, Testosterone next, and Oestradiol (Oestrogen) more loosely than either. It does not carry progesterone in any meaningful way, and it has nothing to do with thyroid hormones, which travel on entirely different carrier proteins. That binding order matters more than it sounds. Because SHBG grips androgens harder than oestrogen, a rise in SHBG reduces active testosterone more than it reduces active oestrogen, which is part of why high SHBG tends to produce androgen-deficiency symptoms in both men and women.

SHBG is sometimes confused with other proteins that sit near it on a blood report, particularly Albumin and total Globulin. They are not the same thing. Total globulin is a broad measure of many proteins, mostly immune ones, while SHBG is one specific carrier with one specific job.

How SHBG affects your testosterone levels

Testosterone results are usually reported as a total, which counts every molecule in the sample regardless of whether it is bound or free. When SHBG is high, that total can look perfectly respectable while the amount reaching the tissues quietly falls short. Take two men who both have a total testosterone of 20 nmol/L. The one with an SHBG of 25 nmol/L has around 11.7 nmol/L of usable testosterone. The one with an SHBG of 70 nmol/L has around 5.9 nmol/L.

An identical testosterone result can mean very different things depending on SHBG. Free testosterone estimated using the Vermeulen method.

Same total, half the usable hormone. This is the single most useful thing SHBG tells you, and it is why a testosterone result should never be read on its own.

SHBG, free testosterone and the free androgen index (FAI)

Because measuring free testosterone directly is expensive and fiddly, most laboratories calculate an estimate instead. The Free Androgen Index (FAI) does this with a simple sum: total testosterone divided by SHBG, multiplied by 100. In the example above, the first man’s FAI is 80 and the second man’s is 29, from identical testosterone results.

In women the index is used slightly differently, as a way of spotting androgen excess. Since low SHBG lifts the index without testosterone production changing at all, a raised FAI often reflects low SHBG rather than a testosterone problem, which is a distinction worth understanding before drawing conclusions from it.

What are normal SHBG levels?

Normal depends heavily on sex and, particularly for men, on age. It also depends on which laboratory processed the sample, which is why two results that look different may in fact be telling the same story.

High results are almost equally common in both sexes. Low results are roughly twice as common in men. Source: Forth customer data.

Worth holding onto before reading any further: the overwhelming majority of results land where they should. Around 8 in 10 sit inside the healthy range, and the proportion coming back high is almost identical for men and women at roughly 9%. It is the low end where the sexes part company.

Normal SHBG levels in men

The healthy range for men at our UKAS-accredited laboratory is 16.5 to 55.9 nmol/L. Across Forth’s male customers the median result is around 30 nmol/L for anyone under 40, sitting comfortably in the middle of that range. Men are more likely than women to return a low result: about 12.6% of male results come back below range, compared with 6.8% of female results. That difference is closely tied to weight and metabolic health rather than to anything about male hormones specifically.

Normal SHBG levels in women

The healthy range for women is 24.6 to 122 nmol/L, which is far wider than the male range and often comes as a surprise. The median result among Forth’s female customers rises with age, from around 52 nmol/L in the early twenties to a peak of around 67 by the early fifties. Roughly 8.7% of female results come back high and 6.8% come back low, so more than eight in ten women land inside the healthy band.

SHBG reference ranges in nmol/L

SHBG is reported in nanomoles per litre almost everywhere in the UK, so conversions are rarely needed. What does change is the range itself. The NHS commonly quotes 15 to 64 nmol/L for men under 50 and 19 to 145 nmol/L for women under 50, while large reference laboratories elsewhere publish their own figures, and none of them are wrong. Ranges are built from the population each laboratory tested, using the specific analyser and assay in its building, so a result should always be read against the range printed beside it. Comparing a number from one laboratory to a range from another is the most common reason people believe they have a problem when they do not.

Even within a single laboratory the limits are not always identical for everyone, since reference ranges can be adjusted for age and sex, which is another reason the range on a report is the one that counts.

SHBG levels by age

The age pattern is one of the clearest signals in Forth’s data, and it looks quite different depending on sex.

In women the median climbs from around 52 nmol/L in the early twenties to a peak of around 67 by the early fifties, which is a gentle slope rather than a steep one, roughly 15 nmol/L spread across three decades. Past the early fifties the climb stops, and levels hold broadly steady through the sixties with the sort of small movement either side that a plateau produces rather than a trend. 

Men follow a different shape entirely. Their median sits around 29 to 30 nmol/L right through the twenties and thirties, barely moving, then lifts from about 40 and keeps lifting, reaching roughly 44 by the early sixties and 49 past 65. By that point a man’s SHBG has risen by about two thirds from where it started. That continuing rise in men matters more than it appears, because it happens at the same time as total testosterone is gently declining. Rising SHBG and falling testosterone pull in the same direction, so the amount of usable testosterone can drop noticeably even when the total still looks acceptable. It is one of the better arguments for tracking these markers together over time rather than testing once and filing the result away.

SHBG levels in pregnancy, perimenopause and menopause

Pregnancy raises SHBG dramatically, driven by the surge in oestrogen, and levels can climb several times above the usual range before returning to normal after birth. That rise is expected and is not a cause for concern on its own.

Menopause moves things far more gently than most people expect. Among Forth’s female customers, the median SHBG is around 59 nmol/L before menopause and around 66 nmol/L after it, a modest step up rather than a jump. Perimenopause is the harder phase to interpret, because oestrogen and progesterone are swinging unpredictably while SHBG drifts slowly upwards in the background, which is exactly why a single snapshot can be so unsatisfying during those years. When symptoms change from month to month, mapping hormones across a full cycle with MyFORM® tells a far more complete story than one measurement ever could.

HRT complicates the picture slightly. Forth’s data shows almost no difference in median SHBG between post-menopausal women taking HRT and those who are not, which reflects the fact that oral and transdermal preparations behave differently. Oestrogen swallowed as a tablet passes through the liver first and pushes SHBG up, while gels and patches largely bypass that route and leave it much closer to where it was.

High and low SHBG levels

High SHBG levels

A high SHBG result means more sex hormone is bound and less is free to work. Around 9% of Forth results come back above range, and in a meaningful share of those cases there is a straightforward explanation that has nothing to do with disease.

What causes high SHBG?

Most of what moves SHBG is something else going on in the body, which is why the cause matters more than the number.

An overactive thyroid is one of the classic drivers, since thyroid hormone directly stimulates the liver to make more SHBG. Liver conditions can do the same, as can pregnancy, older age and certain medicines including some epilepsy treatments and tamoxifen. Very low body weight or a prolonged period of eating far less than your body is using will also push SHBG up sharply, often alongside periods becoming irregular or stopping altogether. Forth’s own results bear this out with some force: among men in the lowest BMI band, 36% return a high SHBG, the single highest rate of out-of-range results anywhere in the dataset, and the figure for women in that band is 15%. 

Anyone in that situation is better served by speaking to a GP than by interpreting the number alone, and organisations such as Beat offer support when food and eating feel difficult.

The most common explanation in women, though, is hormonal contraception, and our data shows something that the general advice tends to blur.

The combined pill more than doubles SHBG. Progesterone-only methods and menopause barely move it. Source: Forth customer data.

Women taking the combined pill or vaginal ring have a median SHBG of around 126 nmol/L, more than double the 59 nmol/L median seen in women using no hormonal contraception. Progesterone-only methods behave completely differently: the median for the mini pill, implant, injection or coil sits at around 50 nmol/L, slightly below the level of women taking nothing at all. 

The flag rates follow the same split, with 14.4% of combined pill users returning a result above the range against 5.3% of women not using hormonal contraception. On the combined pill, a high SHBG result is expected rather than alarming, and it is not evidence that something has gone wrong. The effect is strong enough to run off the end of the scale. Around 7% of combined pill users return a result at or above the laboratory’s reporting ceiling of 200 nmol/L, against well under 1% of women not using hormonal contraception, which is why a report that reads simply as greater than 200 nmol/L is a recognised pattern in this group rather than a cause for concern on its own.

Symptoms of high SHBG in men

When SHBG rises in men, less testosterone reaches the tissues, and the symptoms mirror those of low testosterone even when the total looks fine. Men describe a fading sex drive, erectile difficulties, tiredness that sleep does not fix, low mood and a frustrating loss of strength or muscle despite training as hard as ever.

Symptoms overlap heavily with thyroid problems, perimenopause and simple exhaustion, which is why testing is more useful than guessing.

Symptoms of high SHBG in women

Women with high SHBG often notice symptoms linked to low free testosterone, a hormone women need as much as men do, just in smaller quantities. Low libido is the most commonly reported, alongside vaginal dryness, persistent tiredness, brain fog, low mood and skin or hair that feels drier and thinner than it used to. Because these overlap so heavily with perimenopause, thyroid problems and simple exhaustion, they are frequently attributed to something else for years before anyone measures the hormones involved.

High SHBG with normal or low testosterone

This combination causes more confusion than almost any other hormone result, and it is entirely possible. Total testosterone can sit squarely in the healthy range while SHBG is high and the calculated free testosterone or FAI comes back low. Nothing about that is contradictory. The total is real, the binding is real, and the symptoms are usually being driven by the shortfall in what is left over.

When total testosterone is low and SHBG is high at the same time, the effect compounds, and that picture is worth discussing with a GP rather than acting on alone. The wider point is simple: a normal testosterone result does not rule out a testosterone problem unless SHBG has been measured alongside it.

How to lower your SHBG levels

Treating the number itself is rarely the right approach, because SHBG is a messenger. The far more useful question is what is driving it up, and dealing with that.

If thyroid function is the cause, treating it usually brings SHBG down as thyroid levels settle, so checking Thyroid Stimulating Hormone (TSH), Thyroxine (T4, Free Direct) and Triiodothyronine (T3, Free) is a sensible first step. When the combined pill is behind it and the symptoms are genuinely bothersome, a conversation with a GP or sexual health clinic about switching method is a reasonable one to have, since progesterone-only options do not have the same effect. Where the cause is under-fuelling relative to training load, restoring adequate energy intake tends to bring SHBG back down over a matter of months, and that is a change best made with proper support.

Diet has a real but modest influence. Higher protein intake and adequate carbohydrate are both associated with lower SHBG, while very high fibre intakes and heavily plant-based eating patterns are associated with higher levels. These effects are gentle and slow, so they are better treated as fine tuning than as a fix.

Low SHBG levels

Around 10% of all Forth results come back below range, rising to 12.6% among men. A low SHBG result leaves more free hormone in circulation, which sounds appealing until the usual cause comes into view.

What causes low SHBG?

Low SHBG is one of the most reliable early signals of metabolic strain that a routine blood test can give. Insulin is the key player: when insulin levels are persistently raised, the liver produces less SHBG. That is why low results cluster so tightly around carrying extra weight, insulin resistance, type 2 diabetes and fat accumulating in the liver.

Forth’s data shows the relationship with body weight with unusual clarity. 

SHBG falls steadily as BMI rises, roughly halving across the bands in women. Source: Forth customer data.

Among women, the median SHBG falls from around 76 nmol/L in the lowest BMI band to around 38 nmol/L in the highest, roughly halving. Among men it drops from around 43 nmol/L to around 25 nmol/L across the same bands. Body weight moves SHBG more than almost any other everyday factor, and the gradient is smooth rather than sudden, which means smaller changes are still worth making.

The medians only tell half the story. Looking instead at how often results actually fall outside the healthy range reveals something the averages smooth over, which is that the problem does not simply get worse with weight. It changes direction entirely.

High SHBG dominates at the lowest body weights and low SHBG at the highest, with the two swapping places around a BMI of 25. Source: Forth customer data.

At the lower end of the BMI scale, high SHBG dominates and low results are almost absent. By the time BMI passes 30 the picture has inverted, and among women with a BMI above 35 more than a quarter return a low result, against 2% of women in the 20 to 25 band. The pattern in men is the same shape and arrives earlier, with low results already reaching 14% in the 25 to 30 band. SHBG is not a marker that simply drifts downwards with weight, it sits at the centre of two quite different stories, one about insulin and one about under-fuelling, and which story applies depends on where someone sits on that curve.

An underactive thyroid also lowers SHBG, as does testosterone replacement therapy, long courses of steroid medication and excess growth hormone. In women, Polyendocrine Metabolic Ovarian Syndrome (PMOS) is a frequent finding behind a low result.

SHBG, ethnicity and why one reference range cannot fit everyone

Body weight explains a great deal, but it does not explain everything. South Asian customers, meaning people of Indian, Pakistani and Bangladeshi heritage, return lower SHBG than white customers in every single BMI band, including the band usually described as healthy.

At a BMI between 20 and 25, the median for South Asian women sits at around 51 nmol/L against 68 nmol/L for white women, and for South Asian men at around 28 nmol/L against 38 nmol/L. The gap carries through to how often results fall outside the range: roughly 20% of South Asian women return a low SHBG compared with about 6% of white women, with a narrower difference of 15% against 12% in men.

None of this is a quirk of the biochemistry. It lines up closely with a well-documented pattern in which people of South Asian heritage develop insulin resistance at lower body weights than white populations, which is precisely why NICE recommends lower BMI thresholds for identifying raised risk in this group. Since insulin suppresses SHBG production in the liver, a lower SHBG at a weight that looks entirely unremarkable is a plausible early expression of the same underlying biology.

The practical consequence is worth sitting with, because it cuts against how reference ranges are normally used. Standard SHBG ranges were built largely from white European populations, which means a result sitting comfortably inside the range may be less reassuring for a South Asian reader than the same number would be for someone else, particularly when it sits in the lower half. It does not make the result abnormal, and it is not a prediction about any individual. What it does justify is reading a low-ish SHBG alongside HbA1c and Triglycerides rather than in isolation, and paying attention to the direction of travel across repeat tests rather than to a single position inside a range that was never calibrated on everyone.

Symptoms of low SHBG in men

Men with low SHBG often have no symptoms directly attributable to the SHBG itself, and instead notice the effects of whatever is causing it:

• weight settling around the middle;
• flagging energy;
• mood swings;
• oilier skin;
• and fluid retention. 

The value of a low result here is as an early warning, since it can flag insulin resistance well before blood sugar starts to drift, which is why testing HbA1c alongside it is so informative.

Symptoms of low SHBG in women

In women, low SHBG leaves more free testosterone available, and the symptoms tend to reflect that androgen excess: 

• acne along the jawline;
• oily skin;
• hair appearing where it is least wanted while thinning on the scalp;
• irregular or absent periods;
• and difficulty conceiving. 

These are also the hallmark features of PMOS, which is why the two are so often discussed together.

Low SHBG, insulin resistance and PMOS

The link between low SHBG and PMOS is not a coincidence and it is not really about the ovaries. Insulin resistance is present in a large proportion of women with PMOS, and it does two things at once: it suppresses SHBG production in the liver, and it encourages the ovaries to produce more testosterone. Less binding protein plus more testosterone means considerably more free androgen, which is what produces the acne, the excess hair growth and the disrupted cycles.

A low SHBG result with a raised FAI is one of the recognised biochemical patterns in PMOS, though a diagnosis needs more than a blood test and belongs with a GP or a specialist. Forth’s data adds a small supporting detail: women reporting irregular periods have a slightly lower median SHBG, at around 57 nmol/L, than women with regular cycles at around 61 nmol/L.

Age sharpens the picture considerably. Among women under 30 with a BMI of 35 or above, 47% return a low SHBG, compared with around 2% of lean women of the same age. That is almost half of a group young enough that metabolic problems are rarely looked for, and it matters because low SHBG shifts before blood sugar does. For anyone in their twenties with irregular cycles, acne or unwanted hair growth, that makes a low result early information worth acting on rather than something to revisit once other markers catch up, which usually means looking at HbA1c and the free androgen index in the same panel.

How to increase your SHBG levels naturally

Because low SHBG often reflects insulin resistance, the same changes that improve insulin sensitivity can also help raise SHBG levels:

• Lose excess weight: even modest weight loss can have a measurable effect on SHBG. You do not need to reach an ideal BMI before seeing an improvement.
• Reduce refined carbohydrates and sugar: both can increase insulin levels, which in turn suppress SHBG production. Cutting back may therefore help SHBG rise.
• Eat more fibre: a higher-fibre diet can support better insulin sensitivity and metabolic health, both of which tend to favour higher SHBG levels.
• Check thyroid function: low thyroid function can contribute to lower SHBG, so thyroid testing is worth considering when levels are low without an obvious explanation.
• Focus on exercise that improves body composition and insulin sensitivity: in our data, self-reported weekly training hours showed negligible differences in SHBG levels in both men and women. This suggests that what matters is the effect exercise has on body composition and insulin sensitivity, rather than the number of hours spent training.

Any change deserves a fair run. SHBG responds over months rather than weeks, so retesting after around three months gives a meaningful comparison rather than noise.

What is an SHBG blood test?

An SHBG blood test measures the concentration of the protein in blood, reported in nmol/L, and it is almost always ordered as part of a wider hormone panel rather than on its own. In isolation the number has limited meaning. Read next to the sex hormones it controls, it shows how much of them the body is actually able to use.

Who should test their SHBG levels?

Testing makes sense for anyone with symptoms that point towards too much or too little androgen activity who wants to understand why. For men, that usually means low libido, erectile difficulties, fatigue or a stubborn loss of strength, particularly when a previous testosterone result came back normal and did not explain how they feel. For women, it is often acne, unwanted hair growth, irregular cycles, low libido or the collection of symptoms that arrive in perimenopause and never quite get a name.

It is also worth testing as part of tracking metabolic health, since a falling SHBG is an early and inexpensive signal of insulin resistance. Forth is a preventive service rather than a diagnostic one, so symptoms that are severe, sudden or worrying should start with a GP.

How do Forth tests work?

Forth measures SHBG from a small blood sample collected at home, either by finger-prick or with an AutoDraw device, and posted back in the prepaid envelope provided. Samples are analysed at a UKAS-accredited laboratory to NHS standards, every result is reviewed by the Forth clinical team, and results appear on a secure personal dashboard alongside a written interpretation and the trend across previous tests.

No fasting is required. There is no strict requirement about time of day either, since SHBG is far more stable across the day than Cortisol (9am) or testosterone, although a morning sample is best when SHBG is tested with testosterone, which does follow a clear daily rhythm. For women with regular cycles, days two to five are the usual recommendation when SHBG is measured alongside Follicle Stimulating Hormone (FSH), Luteinising Hormone (LH) and Oestradiol (Oestrogen). Where cycles are irregular or perimenopause has begun, consistency matters more than the exact day.

Two Forth tests include SHBG:

• The Ultimate Health Check Test covers 47 biomarkers across hormones, thyroid, metabolic health, liver, kidneys and nutrition, which places SHBG in the context of the whole system rather than in isolation. 
• The Female Hormone Imbalance Test is a single-day snapshot of the key female hormones alongside thyroid function, including SHBG, oestradiol, testosterone, FSH, LH and prolactin.

How to read your SHBG results

The starting point is the range printed next to the number, not one found online. The next step is to look at the sex hormones beside it, because the pair is where the meaning lives. Three real examples show how this works in practice.

A 54-year-old woman returned a result of 200 nmol/L against a range of 27.1 to 128.0 nmol/L. That is clearly high, and the questions worth asking are about thyroid function, liver health, oral HRT and any medication, rather than about SHBG itself.

A 42-year-old man returned 55.9 nmol/L against a range of 16.5 to 55.9 nmol/L. Technically healthy, sitting exactly on the upper boundary. A result like this is not a problem, but it is a good reason to look at total testosterone and the free androgen index, and to retest in a few months to see which way it is heading.

A man in his thirties returned a result far below the male range. Results that extreme are uncommon and would normally prompt a repeat test to confirm before anything is read into them, followed by a look at weight, thyroid function, blood sugar and any testosterone therapy.

The habit worth building is this: one result is a starting point, and the trend is the story. SHBG moves slowly and steadily, which makes it an excellent marker to follow over years.

What can make your SHBG results fluctuate?

SHBG is stable compared with most sex hormones, but it does drift. Looking at women not using hormonal contraception, Forth’s data traces a clear arc across the cycle: the median sits at around 58 nmol/L during the first few days, climbs to a peak of around 65 nmol/L between days 15 and 21, then eases back to around 60 nmol/L in the days before the next period. SHBG peaks mid-luteal and then settles again, which is a far smaller movement than the swings in Oestradiol (Oestrogen) or Progesterone, though a result taken at the peak can read around 12% higher than one taken during a period. Testing at a similar point each time keeps comparisons honest. 

Starting or stopping the combined pill will move a result substantially. So will pregnancy, significant weight change, a change in thyroid treatment and starting testosterone therapy. Acute illness and heavy alcohol intake can nudge it too. None of this makes the test unreliable. It simply means the circumstances at the time of testing are part of the result.

What biomarkers should I test with SHBG?

SHBG earns its place on a panel by changing how everything else reads, so testing it alone is a wasted opportunity.

• Testosterone (total) is the essential partner, since the two together produce the Free Androgen Index and show how much androgen is genuinely available. 
• Albumin allows a more precise estimate of bioavailable testosterone. 
• Thyroid markers are worth including in almost every case, because both an overactive and an underactive thyroid move SHBG, which makes Thyroid Stimulating Hormone (TSH), Thyroxine (T4, Free Direct) and Triiodothyronine (T3, Free) useful context.
• Oestradiol (Oestrogen), Follicle Stimulating Hormone (FSH), Luteinising Hormone (LH), Progesterone and Prolactin build the fuller female hormonal picture, and Anti-Müllerian Hormone adds ovarian reserve where fertility is the concern. 
• HbA1c is the natural follow-up when SHBG is low, with liver markers such as Gamma GT and Alanine Aminotransferase (ALT) close behind.

FAQs about SHBG