Serum SHBG

Specimen Required

3-5cc Clotted Blood or Serum

Fasting Required

Purpose of the Test

To evaluate whether the concentration of SHBG is affecting the amount of testosterone available to the body’s tissues.

When this test is required

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 but apparently normal levels. Generally Free Androgen calculations are not recommended as first line tests as do not, in most cases, give more information than testosterone levels alone.

What the Test Detects

The Sex Hormone Binding Globulin (SHBG) test measures the amount of SHBG in the blood. SHBG is a protein that is produced by the liver. SHBG binds tightly to the hormones testosterone, dihydrotestosterone (DHT), and oestradiol (an oestrogen) and transports them in the blood in an inactive form. The amount of SHBG in the circulation is affected by age and sex, by decreased or increased testosterone or oestrogen production. It is also affected by certain diseases and conditions such as liver disease, hyperthyroidism or hypothyroidism, by obesity, and by anticonvulsant drugs like phenytoin and phenobarbitone.Changes in SHBG can affect the amount of testosterone that is available to be used by the body. Normally, about 45% of testosterone in men and about 70% in women, is tightly bound to SHBG, and most of the rest is weakly and reversibly bound to another protein, albumin. Only about 1-3% is not bound and immediately available to the tissues as free testosterone.A total testosterone test does not distinguish between bound and free testosterone; it measures the overall quantity of testosterone. In many cases, this measurement is sufficient to discover excessive or deficient testosterone production; but, if a patient’s SHBG level is not normal, then the total testosterone may be misleading.How is the sample collected for testing?A blood sample is obtained by inserting a needle into a vein in the arm.Is any test preparation needed to ensure the quality of the sample?No test preparation is needed.

Preparation for the Test

None

Sample Requirements

A blood sample taken from a vein in your arm

Additional Notes

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 oestrogen 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.

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