SHBG
The Test
How is it used?
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 amenorrhea, infertility, acne, and hirsutism. These symptoms and others are often seen with polycystic ovarian syndrome, a condition characterized 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, estradiol, and LH (lutenizing hormone) may also be performed to evaluate a patient’s existing balance of hormones.
Sometimes, a total testosterone and SHBG are ordered to 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.
When is it ordered?
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?
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 estrogen use (hormone replacement therapy and oral contraceptives). Decreases in SHBG are seen with obesity, hypothyroidism, androgen use, and Cushing’s disease.
