[Lotus]

There is also this, identifying prostate cancer risk factors related to high "bioavailable" SHBG (and low T):

http://www.ncbi.nlm.nih.gov/pubmed/23181478

I would like to understand better the relationship between elevated levels of SHBG and estradiol and prostate cancer risks.

Understanding how and why they test for SHBG:

The test for sex hormone binding globulin (SHBG) is primarily ordered in conjunction with other tests to evaluate the status of a person's androgen levels - the 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.

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 lack of menstruation (amenorrhea), infertility, acne, and male pattern hair growth (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.

Testing for free testosterone, albumin level, and one or more other sex hormones, such as prolactin, estradiol, and LH (lutenizing hormone), may also be performed to evaluate a person'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 (bioavailable testosterone) to SHBG and is calculated as follows: FAI = Total Testosterone / SHBG. In males, a fall in testosterone causes a rise in SHBG, so an FAI or another measure (bioavailable testosterone) is often ordered to detect low levels of free testosterone, which may cause decreased sex drive, loss of muscle mass, decreased bone mass, or occasionally problems with having erections (erectile dysfunction). An elevated FAI may be useful in the evaluation of androgenic alopecia (balding), hirsutism, and severe acne where testosterone levels may be normal.


When is it ordered?
Currently, the SHBG test is not performed frequently or routinely. In many cases, doctors feel that the total testosterone, and perhaps free 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 the SHBG level is 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 the SHBG concentration is decreased, more of the total testosterone is "bioavailable" - not bound to SHBG. This information may be important in the overall evaluation of an individual with signs and symptoms of a condition related to excess or deficient sex hormone production.

Increased levels may be seen in:

Liver disease
Hyperthyroidism
Eating disorders (anorexia)
Estrogen use (hormone replacement therapy and oral contraceptives)
Decreased sex hormone production (hypogonadism)
Decreases in SHBG are seen with:

Obesity
Polycystic ovarian syndrome
Hypothyroidism
Hirsutism
Androgen (steroid) use
Acne
Cushing disease

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.

Testing for 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).
http://labtestsonline.org/understanding/.../shbg/tab/