How is it used?
A sex hormone binding globulin (SHBG) test is primarily ordered to help evaluate the status of a patient’s androgens (male hormones). With men, the issue of concern is testosterone deficiency, while with women the concern is excess testosterone production. A total testosterone may be ordered prior to or along with a SHBG test, which can be useful in determining whether or not a total testosterone measurement is reflecting the amount of testosterone that is available to the body’s tissues.
SHBG and testosterone levels may be ordered on an adult male to help determine the cause of infertility, a decreased sex drive, and erectile dysfunction, especially when total testosterone results are inconsistent with clinical signs.
In women, small amounts of testosterone are produced by the ovaries and adrenal glands. Even slight increases in testosterone production can disrupt the balance of hormones and cause symptoms such as , infertility, acne, and . These symptoms and others are often seen with polycystic ovarian syndrome, a condition characterised by an excess production of androgens. SHBG and testosterone testing may be useful in helping to detect and evaluate excess testosterone production and/or decreased SHBG concentrations.
For both sexes, a free testosterone, albumin level, and one or more other hormones, such as prolactin, oestradiol, and LH (luteinising hormone) may also be performed to help evaluate a patient’s existing balance of hormones.
Sometimes, a total testosterone and SHBG are ordered to help evaluate free androgens by calculating the Free Androgen Index (FAI). This equation gives doctors an idea of the quantity of testosterone that is not bound to SHBG and is calculated as follows: FAI=total testosterone / SHBG x 100.
When is it requested?
Currently, the sex hornmone binding globulin (SHBG) test is not performed frequently or routinely. In many cases, doctors feel that the total testosterone provides sufficient information. SHBG is ordered primarily when the total testosterone results do not seem to be consistent with clinical signs, such as decreased sex drive in men or hirsutism in women.
What does the test result mean?
When SHBG levels are increased beyond what is expected, there is likely to be less free testosterone available to the tissues than is indicated by the total testosterone. If SHBG concentrations are decreased, more of the total testosterone is 'bioavailable' (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 decrease more rapidly in males than in females. Levels are normally stable in adults and then begin to increase in the elderly male at the same time that total testosterone levels begin to decrease. In postmenopausal women, SHBG, testosterone, and estrogen concentrations decrease as hormone production by the ovaries tapers off.
Bioavailable testosterone is becoming an increasingly important concept to both doctors and researchers. It may be measured by removing the SHBG-bound testosterone from the collected blood sample and then analyzing what’s left. An estimate can also be calculated using the Free Androgen Index (see above).
Although SHBG is not usually ordered to diagnose or monitor these conditions, increases in SHBG are seen with liver disease, hyperthyroidism, anorexia, and oestrogen use (replacement and oral contraceptive). Decreases in SHBG are seen with obesity, hypothyroidism, androgen use, and Cushing’s disease.