Testosterone is the principal male sex hormone. In men, it plays an important role in the development of reproductive tissues like the prostate and testis.
It also promotes secondary sexual characteristics such as sexual stamina, deeper voice, aggressive behavior, growth of body hair and increased muscle.
Testosterone is present in 2 forms in the body:
One type is the testosterone which is bound to either Sex Hormone Binding Globulin (SHBG) or to albumin. Both of these are types of proteins which are present in our body. This type of testosterone i.e. the bound form is like a storehouse of testosterone which is used as and when required.
The second type of testosterone is the “free testosterone” which is not bound to anything but moves freely in the body. This “free testosterone” is the one which is readily available for various functions of the body.
Due to the ready availability of free testosterone, it is believed that a measurement of free testosterone is a better indicator of the various effects of testosterone than “total testosterone”.
Generally when you get a hormone test done, you will get to know the level of “total testosterone”. However, a high value of “total testosterone” may not mean that you have good amount of “free testosterone” – the one that is readily available. This is because, out of total amount of testosterone in the body of males, only 1-4% is “free testosterone” while the rest of it if the bound form.
Like most things, Testosterone in men declines with age – look at the figure below to understand the expected average decline.