Test & Diagnostics 31

Why testing your testosterone is more complex than you think

4 min read

Simon Körösi

Reviewed by: Joanna Elmes

Testosterone is a sex hormone that plays a critical role in numerous areas of health. Optimal testosterone levels are essential for muscle development and strength, bone health, sexual function, overall vitality, and athletic performance. Furthermore, in both men and women, testosterone aids in tissue recovery and stimulates the production of red blood cells. Testosterone also facilitates the body's recovery processes. However, excess testosterone can decrease levels of high-density lipoprotein (HDL) cholesterol, also known as "good" cholesterol, potentially impacting heart health and leading to infertility. In contrast, low testosterone may result in fatigue, decreased libido, and diminished athletic performance.

Whilst it is beneficial to know your overall testosterone level, the metabolism of testosterone is complex. Therefore, Supernormal assesses four testosterone-related markers. Taken together, these provide a more comprehensive understanding of how testosterone is functioning within your body.

Total Testosterone - This term refers to the measure of the total amount of testosterone in your bloodstream, incorporating both free testosterone and testosterone that is bound to proteins such as sex hormone-binding globulin (SHBG) and albumin. It signifies the overall concentration of testosterone in your body, irrespective of its binding status.


Free Testosterone – Free testosterone points to the proportion of testosterone that is not attached to any proteins, primarily sex hormone-binding globulin (SHBG) and albumin, within the bloodstream. It is unattached and freely available (making up about 1-2% of the total testosterone), and is viewed as the biologically active form of testosterone that is ready to interact with androgen receptors in target tissues.


Sex-Hormone Binding Globulin (SHBG) - This is a glycoprotein primarily produced in the liver that plays an essential role in the transportation and regulation of sex hormones, including testosterone and oestrogen. Approximately 45% of the testosterone within your body is bound to SHBG. SHBG levels often rise in line with testosterone levels, as it is the protein accountable for regulating sex hormone levels.


Albumin - This protein is the most abundant in human blood and is produced by the liver. The majority of testosterone (around 60-70%) is attached to albumin, forming an albumin-bound testosterone complex. This complex acts as a reservoir of testosterone, making it readily available for use by tissues when required. However, the binding affinity between testosterone and albumin is relatively weak compared to the bond between testosterone and SHBG.

Whilst it's certainly useful and crucial to measure your total testosterone level, gaining insight into the balance between free testosterone, SHBG, and albumin provides you with a much more comprehensive understanding of the quantity of testosterone active in your body, as well as your anabolism/catabolism status. For instance, a high level of SHBG can bind more testosterone, thereby reducing your free testosterone and possibly triggering symptoms akin to those of low total testosterone.