Quick version
SHBG can be the explanation when symptoms and testosterone tests don't quite match up. A man may have fatigue, decreased sex drive or poorer recovery despite total testosterone being within the reference range. Then the question becomes not just how much testosterone is in the blood, but how much is actually available to the body's tissues.
Free vs. bound: How SHBG controls your biological hormone levels
SHBG stands for sex hormone-binding globulin. It is a transport protein that is formed mainly in the liver and that binds testosterone and estradiol in the blood. When testosterone is bound to SHBG, it is not freely available in the same way to the body's tissues, which means that SHBG affects how much biologically active testosterone you actually have.
That's why a regular total testosterone doesn't always give the whole picture. International guidelines recommend that the diagnosis of testosterone deficiency is only made when symptoms are present together with repeated low, correctly measured morning testosterone values, and that free testosterone or calculation of free testosterone becomes particularly relevant when SHBG may be altered.
What does SHBG do in the body?
SHBG functions as a carrier protein. In the blood, testosterone is found in three main forms: bound to SHBG, more weakly bound to albumin and unbound, i.e. free. The free part and a large part of the albumin-bound part are usually considered biologically available, while SHBG-bound testosterone is in practice less available to the tissues.
This explains why two people can have the same total testosterone but feel different. If one has high SHBG, more testosterone is bound, and then the amount of free testosterone can be low despite a “normal” total value. Conversely, low SHBG can make total testosterone appear low, while free testosterone is still sufficient.
In practice, this is common in primary care. A person seeks help for decreased energy and libido, takes a single testosterone test and is told that the value is normal. Only when SHBG, albumin and sometimes calculated free testosterone are added does the hormonal picture become understandable.
When can SHBG give a misleading picture of testosterone?
SHBG becomes especially important when levels are unusually high or low. SHBG and calculation of free testosterone should be used when indicated, precisely to better interpret testosterone values in symptomatic men.
Low SHBG is often seen in:
- overweight and obesity
- insulin resistance and type 2 diabetes
- hypothyroidism"/>
- use of anabolic steroids or certain other hormonal medications
High SHBG can be seen in:
- hyperthyroidism
- underweight or starvation
- drugs or treatments containing estrogen
- liver disease
A concrete example is the man with abdominal obesity and prediabetes. In this case, SHBG is often lowered, which can lower total testosterone. Another example is the slim older man or the person with hyperthyroidism, where SHBG may be elevated and hide low biologically available testosterone levels even though total testosterone does not look alarming.
Symptoms of abnormal testosterone levels when SHBG is involved
SHBG helps interpret testosterone tests and rarely gives clear symptoms in itself. What is noticeable is instead the effect of the free testosterone level becoming too low. Common symptoms of testosterone deficiency in men can be reduced sex drive, fewer spontaneous morning erections, erection difficulties, fatigue, reduced physical energy, depression and reduced muscle mass. The diagnosis should not be based on test results alone, but on the combination of symptoms and repeated low testosterone values.
It is easy to misinterpret these cases. A man with high SHBG may be told that testosterone is 'normal' despite clear symptoms, while a man with low SHBG may have a low total value without actually having any pronounced lack of free testosterone. The diagnosis should therefore never be based on test results alone, but on the combination of the patient's symptoms and correctly correlated tests.
For women, SHBG is also used in hormone assessment, but more often when there is suspicion of androgen excess, for example in case of irregular menstruation, acne or increased hair growth. This article focuses on testosterone levels in men, where SHBG primarily helps to interpret suspected hypogonadism.
The right test at the right time - this is how the hormone balance is investigated correctly
If testosterone deficiency is suspected, testosterone should be taken in the morning, usually on an empty stomach and preferably between around 7 and 10 a.m., as levels vary throughout the day. It is recommended that low values are confirmed with a new morning test before a diagnosis is made.
A well-thought-out hormone test often contains total testosterone and SHBG, and sometimes albumin to be able to calculate free testosterone. If testosterone deficiency is further suspected, LH and FSH may also be needed to determine whether the problem is in the testicles or in the pituitary-hypothalamus system. Prolactin may also be relevant in cases of low sex drive or signs of secondary hypogonadism.
This is particularly valuable if you:
- have symptoms despite normal total testosterone
- are overweight, diabetic, have thyroid disease or liver disease
- want to follow up on hormonal changes over time
- are considering testosterone treatment and need a more reliable baseline
Fatigue, low energy, sleep problems and depression often have multiple causes, but a structured health check can identify whether hormonal abnormalities are part of the picture. This will make the investigation more accurate and reduce the risk of both overtreating and missing treatable conditions.
What can you do if SHBG or testosterone deviates?
Treatment is not directed at SHBG as an isolated laboratory value, but at the cause and clinical consequence. If SHBG is low due to obesity, insulin resistance or type 2 diabetes, you often need to start with the metabolic whole. If SHBG is high, you may need to investigate the thyroid gland, liver function, nutritional status or medication.
Lifestyle changes can play a major role, especially in functional testosterone reduction linked to abdominal obesity, lack of sleep and metabolic disease. At the same time, you should not assume that all problems will be solved with testosterone. Testosterone treatment is only recommended for clear symptoms together with consistently low, correctly measured testosterone values, and treatment is advised against if fertility is desired in the near future or if certain risk factors are present.
It is also worth knowing that testosterone treatment is not a general energy treatment. Treatment can improve several sexual symptoms in men with documented hypogonadism, but the benefit is less well documented in people without true testosterone deficiency.
In practice, this means that the right diagnosis comes before the right treatment. A well-planned blood test can show whether you need lifestyle support, further medical investigation or follow-up with a doctor, instead of guessing based on a single hormone value.
