Free Testosterone Calculation is a measurement of the amount of free testosterone in the body. It is a steroid hormone produced by the male testes and the adrenal glands in both men and women. It regulates the male sex drive and maintains muscle mass. Free testosterone calculation is used in the diagnosis of various conditions such as erectile dysfunction and infertility in men.

Sex Hormone Binding Globulin (SHBG) is a protein produced by the liver. Its main function is to bind and transport the hormones oestradiol, testosterone and dihydrotestosterone in the blood. The SHBG test is used to diagnose testosterone deficiency in men and is used to investigate the production of testosterone in women.

Testosterone is an important sex hormone for both men and women. In men, it is made in the testicles. In women, it is made in small amounts in the ovaries.  

It is important for normal male sexual development. During puberty (in the teen years), testosterone helps boys develop male features like body and facial hair, a deeper voice, and muscle strength. Too much testosterone in men can cause shrinking of the testicles, impotence, an increased risk of heart attack and prostate enlargement with difficulty urinating. Too little can cause fatigue, irritability, depression, erectile dysfunction and reduced muscle mass. 

Combined with oestrogen, testosterone helps with the growth, maintenance, and repair of a woman's reproductive tissues and bone mass. Too much can cause acne, excess hair on the face and body, irregular periods and mood changes. Too little can cause low libido and weight gain.