Also known as: testosterone-oestrogen-binding globulin (TeBG)
Name: sex hormone-binding globulin
Related tests: Testosterone
Why get tested?
To assess whether the SHBG concentration is affecting the amount of testosterone available to the body’s tissues
When to get tested?
When total testosterone results do not match the clinical signs suggesting a lack or excess of testosterone
Sample required?
A blood sample taken from a vein in the arm
What is being tested?
The SHBG test measures the concentration of SHBG in the blood. SHBG is a protein produced by the liver. It binds tightly to testosterone, dihydrotestosterone (DHT) and oestradiol (an oestrogen) and transports them in the blood in a metabolically inactive form. The amount of SHBG in circulation is affected by age and sex and by increased or decreased production of testosterone or oestrogens, and it can be affected by certain diseases and conditions such as liver disease, hyperthyroidism or hypothyroidism, and obesity.
Changes in SHBG levels can affect the amount of testosterone available for use by the body’s tissues. Normally, about 40-60% of testosterone is bound to SHBG, and most of the rest is loosely and reversibly bound to albumin. Only about 2% is immediately available to the tissues as free testosterone.
The total testosterone test does not distinguish between bound and unbound testosterone; it measures the overall amount of testosterone. In many cases this is enough to assess whether testosterone production is excessive or deficient; however, if a patient’s SHBG level is abnormal, total testosterone may not accurately reflect the amount of testosterone available to the patient’s tissues.
How is the sample collected for testing?
A blood sample is taken with a needle from a vein in the arm
How is it used?
When is it requested?
What does the test result mean?
Is there anything else I should know?
How is it used?
The SHBG test is used primarily to assess a patient’s androgen (male hormone) status. In men, the concern is testosterone deficiency, while in women the problem is excess testosterone production. A total testosterone test may be requested before or together with the SHBG test.
SHBG and testosterone levels may be requested for an adult man to help determine the cause of infertility, reduced sex drive and erectile dysfunction, especially when total testosterone results do not agree with the clinical signs.
In women, small amounts of testosterone are produced by the ovaries and adrenal glands. Even slight increases in testosterone production can upset the hormonal balance and cause symptoms such as amenorrhoea, infertility, acne and hirsutism. These and other symptoms are often seen with polycystic ovary syndrome, a condition characterised by excess androgen production. SHBG and testosterone tests can help detect and assess excess testosterone production and/or reduced SHBG concentrations.
In both sexes, tests for free testosterone, albumin and one or more other hormones, such as prolactin, oestradiol and LH (luteinising hormone), may also be carried out to assess a patient’s overall hormonal balance.
Sometimes total testosterone and SHBG are requested to assess free androgens by calculating the free androgen index (FAI). This equation gives doctors an idea of the amount of testosterone not bound to SHBG and is calculated as follows: FAI = total testosterone / SHBG.
When is it requested?
At present, the SHBG test is not carried out frequently or routinely. In many cases, doctors feel that total testosterone, and perhaps free testosterone, provide enough information. SHBG is requested mainly when total testosterone results do not seem consistent with the clinical signs, such as reduced sex drive in men and hirsutism in women.
What does the test result mean?
When SHBG levels are higher than expected, there is probably less free testosterone available to the tissues than the total testosterone suggests. If SHBG concentrations are low, more of the total testosterone is “bioavailable”, i.e. not bound to SHBG.
Is there anything else I should know?
SHBG concentrations are normally high in children of both sexes. After puberty, SHBG levels fall more quickly in males than in females. Levels are usually stable in adults and then start to rise in older men at the same time as total testosterone levels start to fall. In women after the menopause, SHBG, testosterone and oestrogen concentrations fall as hormone production by the ovaries declines.
Bioavailable testosterone is becoming an increasingly important concept for both doctors and researchers. It can be measured by removing the SHBG-bound testosterone from the blood sample and then analysing what remains. It can also be estimated using the FAI (see above).
Although SHBG is not usually requested to diagnose or monitor these conditions, increased SHBG is found in liver disease, hyperthyroidism, anorexia and oestrogen use (hormone replacement therapy and oral contraceptives). Decreased SHBG is found in obesity, hypothyroidism, androgen use and Cushing’s disease.
1. Are there other uses for the SHBG test?
2. Can I change my SHBG level?
1. Are there other uses for the SHBG test?
Not yet, but researchers are studying conditions in which testosterone and SHBG levels change to see whether the test may have further clinical uses.
2. Can I change my SHBG level?
Not directly, and there is no reason to do so. SHBG is used to assess a patient’s hormonal balance. In some cases, testosterone and/or oestrogen replacement therapy may be used to correct a deficiency. Researchers are now exploring the benefits and risks of testosterone replacement in older men (men in andropause) and in women after natural or surgical menopause. It will take time to establish whether and when this treatment is safe, effective and clinically useful.