SHBG

SHBG is measured to find the status of the patient’s testosterone in the blood. In men it is used to look for testosterone deficiency.  In women it is used to investigate excess production of testosterone. A total testosterone test is used at the same time as the SHBG test.

SHBG and testosterone levels may be used on an adult man to help discover 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 are often seen with polycystic ovarian syndrome, a condition which has an excess production of androgens like testosterone. SHBG and total testosterone testing may be useful in helping to detect and investigate excess testosterone production and/or decreased SHBG levels.

For both sexes, one or more other hormones, such as prolactin, oestradiol, and LH (luteinising hormone) may also be measured to 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, or by dividing the testosterone result by the SHBG result to give what is called the Free Androgen Index (FAI=Total testosterone/ SHBG).

In most cases the total testosterone measurement gives sufficient information.  SHBG is normally used when the total testosterone results do not seem to fit with clinical signs, such as decreased sex drive in men or 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. This could lead to poor libido in men.

If SHBG concentrations are decreased, more of the total testosterone is available to the tissues.  In women this could lead to hirsutism.

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 decreases.

Some laboratories calculate bioavailable testosterone from the total testosterone and SHBG results.  Bioavailable testosterone is the free testosterone plus the testosterone bound to albumin.  Since testosterone is loosely bound to albumin it has been suggested that it is also available to tissues and should be also considered.  It gives the same information as calculated free testosterone and the FAI.

Although SHBG is not usually used to diagnose or monitor these diseases, increases in SHBG are seen with liver disease, hyperthyroidism, anorexia, and oestrogen use (hormone replacement therapy and oral contraceptives). Decreases in SHBG are seen with obesity, hypothyroidism, androgen use, and Cushing’s disease.