Testosterone is a notorious hormone that plays magic with muscles and masculinity. Testosterone has nothing to do with libido or increasing muscle mass, but it can regulates mood and bone strength.
It is normal to have steady and slow drop in blood testosterone level as a part of aging. Many times it does not show up any significant symptoms. But some may notice lack of libido, hot flash or mood swing. In most of the men fall in testosterone level can show up some changes like, thinner muscles, breast enlargement, loosing body hair, testicles become soft and small.
Low testosterone levels can cause osteoporosis in men. Osteoporosis is a condition that makes the bones thinner, weaker, and brittle.
All though testosterone has nothing to do with sex, but it makes the brain and body difficult to get sexually stimulated. Fall in testosterone makes it difficult to maintain erection. Testosterone is an essential component for the sperm production in the tentacles. Hence low level can lead to low sperm count and infertility.
All though getting older is the major cause, but some illnesses can also lead to fall in testosterone levels, including: diabetes, liver disease, injuries of testicles, and disease of pituitary gland.
Blood is used to test the Testosterone level and usually done in the morning. Level is said to be normal if it ranges between 300 - 1,000 ng/DL.