SHBG, or sex hormone binding globulin, is a transport protein that is mainly produced in the liver. It binds sex hormones in the blood, especially testosterone and estradiol, and affects the proportion of hormones that are free and available to the body's tissues.
The blood test measures the concentration of SHBG in serum. The analysis is usually used together with testosterone to provide a more accurate picture of the body's androgen status. A testosterone value within the reference range does not always mean that the amount of available testosterone is normal.
Why is SHBG analyzed together with testosterone?
The majority of testosterone in the blood is bound to SHBG or albumin. Only a small proportion circulates as free testosterone. Testosterone that is strongly bound to SHBG is usually not considered directly biologically available, while the free and albumin-bound proportion can more easily reach the body's tissues.
The SHBG value therefore affects how a total testosterone value should be interpreted. A high SHBG may mean that a smaller proportion of testosterone is free, even if the total testosterone is normal or high. A low SHBG may instead mean that a larger proportion is available, which means that a low total testosterone does not always correspond to a true testosterone deficiency.
What can an SHBG test show?
The analysis can help explain symptoms or test results that are not consistent with the level of total testosterone. By assessing SHBG together with testosterone and sometimes albumin, the amount of free testosterone can be estimated or calculated.
SHBG may be relevant in the investigation of suspected testosterone deficiency in men and in signs of androgen excess in women. The analysis can also be used to investigate, for example, irregular menstruation, increased hair growth, acne, decreased libido, erectile dysfunction, reduced muscle mass or fertility problems.
What can affect SHBG levels?
SHBG is affected by several hormonal, metabolic and medical factors. A deviating value is therefore not a diagnosis in itself but needs to be interpreted together with symptoms, other test results, medications and health conditions.
Elevated SHBG can occur, among other things, in
- increased estrogen exposure, for example during pregnancy or during treatment with estrogen
- hyperthyroidism, i.e. overfunction of the thyroid gland
- certain liver diseases
- increasing age, especially in men
- low body weight or malnutrition
- treatment with certain medications
Low SHBG can occur, among other things, in
- overweight and insulin resistance
- metabolic syndrome and type 2 diabetes
- hypothyroidism, i.e. underfunction of the thyroid gland
- androgen excess, for example in polycystic ovarian syndrome (PCOS)
- treatment with testosterone, anabolic steroids or certain other drugs
When may it be relevant to check SHBG?
A SHBG test may be relevant when a testosterone level is low, high or difficult to interpret, or when symptoms do not correspond to the level of total testosterone. The analysis can provide additional information in the following cases:
- suspected testosterone deficiency
- reduced libido or erectile dysfunction
- reduced muscle mass, strength or recovery
- fertility investigation
- irregular or absent menstruation
- increased hair growth, hair loss or acne in women
- suspected PCOS or other androgen disorder
- follow-up of hormonal treatment
How is an SHBG value interpreted?
A SHBG value should not be interpreted in isolation. The assessment is most informative when the value is analyzed together with total testosterone and, if necessary, albumin, LH, FSH, prolactin, estradiol and thyroid samples.
In men with suspected testosterone deficiency, testosterone testing is usually recommended in the morning, since testosterone levels vary throughout the day. The diagnosis of testosterone deficiency cannot be made based on SHBG or a single testosterone value alone, but requires a comprehensive medical assessment of symptoms and repeated test results.
Important to know
SHBG does not in itself show how much testosterone the body produces. Instead, the test helps to assess how much of the testosterone is bound and how the total testosterone should be interpreted. A high or low SHBG therefore does not necessarily mean that there is a disease.
For a more complete assessment of testosterone status, it is recommended that SHBG be analyzed together with testosterone. In the event of deviating results or clear symptoms, the test result should be discussed with a doctor.
