A sex hormone binding globulin (SHBG) test is primarily ordered to help evaluate the status of a patient’s androgens (male hormones). In men, it is used to look for testosterone deficiency. In women it is used to investigate excess production of testosterone. 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 like testosterone. 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.
When testosterone and SHBG are measured together the laboratory will usually estimate the amount of free testosterone. This may be done using a mathematical formula, such as the Vermeulen equation, or by dividing the testosterone result by the SHBG result to give what is called the Free Androgen Index (FAI= Total testosterone /SBHG x 100).
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 infertility, decreased sex drive, and erectile dysfunction in men or infertility, irregular menstrual periods, and excess facial and body hair (hirsutism) in women.
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). 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 SHBG levels may be seen in:
- Liver disease
- Eating disorders (anorexia nervosa)
- Corticosteroids or oestrogen use (hormone replacement therapy and oral contraceptives)
- Decreased sex hormone production (hypogonadism).
Decreased in SHBG may be seen in:
- Polycystic ovary syndrome
- Androgen (steroid) use
- Cushing's syndrome
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.