SHBG, or sex hormone-binding globulin, is a protein that attaches to testosterone in your bloodstream. Because testosterone bound tightly to SHBG isn’t readily available for your tissues to use, SHBG levels can influence how much free testosterone your body has. This is one reason hormone testing may involve more than checking total testosterone alone.
Board-certified family nurse practitioner Russ Henderson, FNP-BC, is the Founder and Clinical Director of Oregon Man Clinics. A U.S. Air Force veteran with a background in urology, he works with men seeking care at locations in Bend, Springfield/Eugene, Albany, Ontario, and Roseburg, OR.
What Does SHBG Do?
Most testosterone in your blood is attached to proteins. SHBG binds testosterone strongly, while albumin binds it more loosely. A small portion circulates unbound as free testosterone.
Free testosterone is readily available for tissues to use, while testosterone loosely bound to albumin may also be biologically available. Because SHBG affects this balance, two men with similar total testosterone levels can have different amounts of free testosterone.
How Does SHBG Affect Testosterone Test Results?
Total testosterone measures testosterone circulating in different forms, including testosterone bound to SHBG. When SHBG is unusually high or low, the total testosterone result may not fully reflect the amount available to your tissues.
Higher SHBG generally means a greater proportion of testosterone is tightly bound, potentially leaving less free testosterone. Lower SHBG can mean a greater proportion remains free or loosely bound.
For this reason, your provider may consider your symptoms alongside total testosterone, free testosterone, SHBG, your medical history, and other laboratory findings rather than relying on one number.
What Can Affect SHBG Levels?
Several factors can influence SHBG levels, including age, body composition, thyroid function, liver health, metabolic health, medications, and other hormonal factors.
An abnormal SHBG result isn’t a diagnosis on its own. Instead, it can provide additional context when interpreting testosterone levels, particularly when symptoms and total testosterone results don’t seem to match.
Why Does SHBG Matter When Evaluating Low Testosterone?
Diagnosing testosterone deficiency generally involves both symptoms and consistently low testosterone measurements. When SHBG may be affecting total testosterone results, measuring or calculating free testosterone can provide additional information about your hormone status.
For men receiving testosterone replacement therapy, follow-up testing also helps providers evaluate hormone levels and the response to treatment over time.
Learn More About Your Hormone Health
Understanding the relationship between total testosterone, free testosterone, and SHBG can provide a clearer picture of your hormone health. To discuss testosterone testing and hormone replacement with Oregon Man Clinics, schedule a consultation at one of five locations in Bend, Springfield/Eugene, Albany, Ontario, or Roseburg, OR.