Testosterone Replacement Therapy Primer
Below is a alphabetical list of testosterone replacement therapy terms. Each post will allow the user to hover over certain words, leading to a popup definition. These definitions can also be found below.
Albumin: This is a serum blood plasma protein produced in in the liver and has many different functions. It is part of a standard CBC blood test your doctor can order. Testosterone binds weakly to this protein and is easily removed to make more T available for biological functioning. The blood test will uncover issues with Albumin serum levels, however this test is not the same as the bioavailable testosterone test which includes as part of its result the amount of protein bound to Albumin, which is then added to the amount of free serum testosterone to discern the amount of testosterone available to the body that is bioactive (not bound up or tied up to other molecules, i.e. the sexual hormone binding globulin (SHBG). The reported number includes the sum of these values.
Bioavailable Testosterone: Bioavailable T is a measure of the amount of testosterone bound weakly to Albumin and free testosterone. This amount is is what is can be made biologically available to the body.
Sexual Hormone Binding Globulin (SHBG): This is a protein that binds to the sex hormones testosterone and estradiol. SHBG is primarily produced by the liver and secreted into the blood where its plasma levels can be measured. Testosterone strongly binds to this protein and therefore T that is bound to SHBG is not biologically available to the body. As SHBG is really a measure of a complex balancing of hormones that is active in the body, it is not advisable to attempt to raise or lower SHBG with medications except in some cases. As we age, SHBG bound T tends to raise, lowering the amount of testosterone that is available to the body. Males of certain ethnicities may posses a genetic blueprint that leads to high SHBG at an early age. Usually progesterone is used to lower SHBG in this subset of patients. Low SHBG is often an indicator of other issues. For example, insulin resistance is often associated with low SHBG. Medically lowering SHBG in this case by the use of supplements or drugs is contraindicated. If the underlying cause is addressed, the amount of SHBG will raise. Low SHBG often leads to high levels of Free-T and Bioavailable-T. The body will dump this excess Free-T into estrogens and the amount of Total-T will lower. Therefore, patients with low SHBG due to a medical issue will often find high levels of Free-T and low levels of Total-T. In some cases, if the Free-T is high normal and Total-T is low normal, the patient may be better advised to lose weight and diet before attempting TRT. In many cases, the androgen system and testosterone levels can return to normal vales.
Selective Estrogen Receptor Modulator (SERM): A class of drugs that acts on the estrogen receptors to selectively stimulate or inhibit estrogen activity in various tissues. Of interest in testosterone replacement therapy is the use of two particular SERMS – Clomiphene Citrate (Clomid) and Tamoxifen (Nolvadex). Some post-cycle therapy (PCT) protocols use both SERMs together, some do not. Some also use human chorionic gonadotropin (HCG) while on TRT prior to a PCT while other protocols use HCG prior to SERM use. There are many PCT protocols out there for those whose hypothalamic-pituitary-testicular axis (HPTA) are intact. Stopping TRT is always challenging and some protocols work better than others.
Total Testosterone: Total T is a serum blood test used to measure the amount of testosterone that is strong bound to Sexual Hormone Binding Globulin (SHBG), loosely bound to Albumin, and the remaining Free Testosterone. As testosterone is loosely bound to Albumin, another measure, Bioavailable Testosterone is the measure of Free Testosterone + the amount of testosterone bound to Albumin. In other words, if your body needs it, it will rip the testosterone off Albumin. To summarize Total T is the equivalent of Free-T + T bound to SHBG + T bound to Albumin.