Sex Hormone Binding Globulin and Testosterone
When testosterone blood tests are ordered by a physician, he or she may also measure your Sex Hormone Binding Globulin (SHBG). Put simply SHBG is the the carrier molecule which transports sex-steroids, like testosterone, within in the bloodstream and around the body. Current research points to a more complex scenario, however it can be used as a laboratory marker to diagnosis and monitor conditions involving testosterone.
SHBG is synthesized in the liver, it is also produced by the placenta of pregnant women who will have higher SHBG levels during pregnancy. SHBG has binding sites on its surface which hold tight to sex-steroids with the highest affinity for dihydrotestosterone (DHT), then testosterone and then oestrogens. When testosterone is bound to SHBG it is said to be ‘inactive’ meaning it is not ‘free’ or bioavailable to act on targets tissues. There is a delicate and complex balance that occurs within the body between the sex-steroids for these binding sites so when the amount of SHBG alters from the norm various hormonal conditions may arise.
For men, SHBG levels are stable through adulthood until mid to late life when it then increases, at the same time testosterone begins to decrease. This combination of high SHBG and low testosterone may lead to late onset hypogonadism which can benefit from testosterone replacement therapy.
Your blood test may also include the Free Androgen Index (FAI). It is calculated by dividing total testosterone (x100) by SHBG and approximates how much of the testosterone is ‘free’ testosterone. It is not a good predictor if SHBG is particularly low.
Common Laboratory Values
These values are a guide to the ‘normal’ range for men and non-pregnant women, the laboratory processing your blood test may have a slightly different reference range.
|Unit of Measure||Normal Adult Male||Normal Adult Female|
|ng/dL||375 to 1,200||
28 to 80
|nmol/L||10 to 35||
1.0 to 2.8
|pg/mL||50 to 175||
1.3 to 6.8
|175 to 600||
4.5 to 23.6
|nmol/L||10 to 57||
18 to 144
|Free Androgen Index (FAI)||>75||
7 to 10
Interpreting SHBG Results
A fall in testosterone may cause a rise in SHBG, this in turn can reduce the amount of ‘free’ testosterone. In both men and women the following symptoms may arise, low libido, increased abdominal fat, decreased mood and lack of energy. In these cases testosterone replacement may be considered. On the other hand if SHBG is low and there is more ‘free’ testosterone then signs of testosterone excess can arise such as androgenic balding, increase hairiness and acne. This scenario of low SHBG and high free testosterone is often seen in polycyctic ovarian syndrome where treatment may involve anti-androgen (testosterone) therapy.
Occasionally when SHBG is high it can hinder the effects of testosterone creams. In these cases where the total testosterone levels is within normal to high range and symptoms are still apparent then further investigation as to why SHBG is high may be considered. Some lifestyle measures may be beneficial to reduce SHBG such as stopping smoking.
Research has also shown that SHBG may be a predictor for type 2 diabetes. Those individuals with insulin resistance or at high risk of type 2 diabetes that have low SHBG are more likely to progress to type 2 diabetes. This begs the question whether increasing SHBG levels therapeutically will prevent type 2 diabetes. Current research is being conducted in the T4DM study using testosterone in men with pre-diabetes to answer some of these questions.
You may see increased SHBG levels in;
- oestrogen replacement including HRT (more likely when given orally)
- oral contraceptive use
- liver disease
- eating disorders such as anorexia
You may see decresed SHBG levels in;
- polycycstic ovarian syndrome
- steroid use
- cushing disease
It is recommended that after starting testosterone replacement therapy such as Androforte or Androfeme, blood levels are taken three to four weeks after commencement of therapy and then once or twice a year thereafter. In conjunction with blood tests it is also important to consider how you are responding to testosterone therapy. If you are feeling a benefit then don’t get too ‘caught up’ in the numbers (unless they are very high or your doctor is concerned) because as individuals we may respond in different ways.
If you would like to learn more about Lawley Pharmaceuticals Testosterone for Men and Testosterone for Women , please click on the booklets below.