It is suggested that bioavailable testosterone represents the fraction of circulating testosterone that readily enters cells and better reflects the bioactivity of testosterone than does the simple measurement of serum total testosterone. Also, varying levels of SHBG can result in inaccurate measurements of bioavailable testosterone. Decreased SHBG levels can be seen in obesity, hypothyroidism , androgen use, and nephritic syndrome (a form of kidney disease ). Increased levels are seen in cirrhosis , hyperthyroidism , and estrogen use. In these situations, measurement of free testosterone may be more useful.
Signs of low testosterone in men may include decreased sex drive, erectile dysfunction (ED), lowered sperm count or increased breast size. Men also may have symptoms similar to those seen during menopause in women – hot flashes, increased irritability, inability to concentrate and depression. Some men may have a prolonged and severe decrease in testosterone production. As a result, they may experience loss of body hair and reduced muscle mass, their bones may be more brittle and prone to fracture, and their testes may become smaller and softer. In younger men, low testosterone production may reduce the development of body and facial hair, muscle mass and genitals. In addition, their voices also may fail to deepen. Women may experience a decrease in sex drive, lack of energy, decreased “enjoyment of life”, and even depression.