What Is Sex Hormone Binding Globulin?

Medically Reviewed by Jabeen Begum, MD on November 22, 2021
3 min read

Sex hormone binding globulin (SHBG) is a protein in your blood that binds certain hormones. It’s produced in the liver and—in smaller amounts—in the testes. 

It’s an ancient protein that’s found in all mammals. There are even versions of it in fish. 

The job of this protein is to control the amount of certain other hormones in your blood and determine which tissues these hormones can access.   

Sex hormone binding globulin binds three hormones that are found in males and females: 

  • Testosterone. This is the main sex hormone for males, but is also found in females.
  • Dihydrotestosterone. This is also found in greater quantities in males.
  • Estradiol. This is a form of estrogen—the main female sex hormone. 

Testosterone and estrogen are important hormones that help your body develop its sexual and reproductive tissues. SHBG is a necessary protein that helps move the active — i.e., working — versions of these hormones throughout your body. 

The sex hormone binding globulin test is an SHBG blood test. Your doctor will use this test to measure the levels of the SHBG protein in your blood. It’s commonly done at the same time as other tests that look at testosterone levels. 

The blood test itself is simple and should take less than five minutes.

Your doctor will usually order these tests when they suspect that your testosterone levels are abnormal. For males, that may mean your testosterone levels are too low. For women, your levels may be too high.   

Be sure to tell your doctor if you take any supplements, opioids, recreational drugs, or have an eating disorder. All of these things can change the results of this test, so it’s important for your doctor to know about them before you take it.  

Children usually have very high levels of SHBG, so the test is only for adults. 

Sex hormone binding globulin levels can vary from person to person, and they change in amount throughout your lifetime. Factors that impact your normal levels of SHBG include: 

  • Sex
  • Age
  • Weight
  • Genetics
  • Metabolism

A number of conditions can result from having too much or too little SHBG. Your doctor will need to take all of these factors into account—as well as any other symptoms you have—in order to decide whether or not your level of SHBG is normal for you.  

When your sex hormone binding globulin levels are low, that could indicate that you have one of the following conditions, including: 

  • Hypothyroidism. When your thyroid doesn’t produce enough thyroid hormone.
  • Cushing’s syndrome. This is when your body makes too much cortisol.
  • Type II diabetes. A disease where your body has problems regulating your blood sugar levels. 
  • Cancer in the testes. This is only a possibility in males. 
  • Polycystic ovary syndrome. This is a hormone disorder in females that can lead to infertility.

When you have high sex hormone binding globulin levels, it could indicate that you have one of the following conditions, including: 

  • Hyperthyroidism. When your thyroid makes too much thyroid hormone. 
  • Pituitary problems. This is a gland located beneath the brain that controls many important bodily functions. 
  • Addison's disease. This is when your adrenal glands don’t make enough of particular hormones. 

Sometimes, your doctor will find it helpful to compare SHBG levels to total testosterone levels in your body. This will give them an estimate of how much of your body’s testosterone is currently in use. Problems with your ratio of SHBG to testosterone could indicate particular conditions, including:  

  • Androgen deficiency. Androgen is another hormone. When levels are low, symptoms vary between males and females. 
  • Hypogonadism. A condition found mostly in males that leads to low testosterone levels. 

Each of these conditions has its own treatment. Your doctor will probably not be able to determine your underlying condition from this sex hormone binding globulin test alone. 

If your test shows abnormal levels of SHBG, your doctor will need to collect more information in order to decide what is causing this problem. Then, they’ll create a treatment plan that’s unique to your particular situation.