TRT Monitoring with Free Testosterone Blood Test

Testosterone is a hormone that causes male characteristics. For men, it helps to regulate sex drive and has a role in controlling bone mass, fat distribution, muscle mass, strength and the production of red blood cells and sperm. Testosterone is produced in the testicles of men and, in much smaller amounts, in the ovaries of women. Testosterone levels in men naturally decline after the age of 30, although lower than normal levels can occur at any age and may be associated with low libido, erectile dysfunction, difficulty in gaining and maintaining muscle mass and lack of energy. During TRT, monitoring total testosterone helps ensure levels are within the therapeutic range—neither too low (ineffective treatment) nor too high (increased risk of side effects).

Most testosterone circulating in the blood is bound to proteins, in particular SHBG and albumin; only 2–3% of testosterone is free and available to cells. This test uses an algorithm to calculate the level of free or unbound testosterone in relation to total testosterone, SHBG and albumin. Free testosterone is considered by many clinicians to be a more accurate reflection of testosterone availability to tissues than total testosterone alone. During TRT, free testosterone levels help assess whether the treatment is effectively delivering bioavailable hormone to your cells, regardless of changes in binding proteins.

Oestradiol is the strongest of the three oestrogens. It's labelled a female hormone but it's made in both the ovaries and testes. It's responsible for the growth of breast tissue, the female reproductive system, and male sexual function. In men, oestradiol levels tend to increase slightly with age as testosterone levels decline. Elevated oestradiol in men may be associated with fertility problems, gynaecomastia (enlarged breast tissue), and erectile dysfunction. During TRT, some testosterone is converted to oestradiol by the aromatase enzyme. Monitoring oestradiol is important because elevated levels can cause side effects such as water retention, mood changes, and gynaecomastia, and may require treatment adjustment or the addition of an aromatase inhibitor.

Prolactin is a hormone produced in the pituitary gland and plays a role in reproductive health. Its primary purpose is to stimulate milk production after childbirth, and in pregnant and breastfeeding women prolactin levels can soar. Elevated prolactin levels in men may be associated with low libido, erectile dysfunction, and reduced testosterone production. During TRT, prolactin is monitored because elevated levels can indicate pituitary problems or can occur as a side effect of certain medications. High prolactin can also suppress testosterone production and reduce the effectiveness of TRT.

SHBG (sex hormone binding globulin) is a protein which transports the sex hormones (testosterone, oestrogen and dihydrotestosterone) in the blood. Hormones which are bound to SHBG are inactive, meaning they are unavailable to your cells. Measuring SHBG gives important information about your levels of free or unbound hormones which are biologically active and available for use. High SHBG reduces the amount of free testosterone available to tissues, while low SHBG increases it. SHBG levels can be affected by age, obesity, liver disease, thyroid conditions, and certain medications. During TRT, SHBG helps interpret whether total testosterone levels are translating into adequate free testosterone.

Albumin is a protein made mainly in the liver. It helps to exert the osmotic pressure which holds water within the blood, carries nutrients and medications through the blood, and is important for tissue growth and healing. Albumin also carries hormones around the body—testosterone binds loosely to albumin, and this albumin-bound testosterone is considered bioavailable (unlike SHBG-bound testosterone). Measuring albumin allows for accurate calculation of free testosterone using established algorithms. Albumin levels can be affected by liver disease, kidney disease, malnutrition, and inflammation.