While testosterone is inherently considered to be a male sex hormone, minimal amounts of it are also found in women. This hormone helps in bone and muscle development, sperm production, hair growth, deepening of the voice and other characteristics that relate to appearance. Although it is a natural phenomenon for testosterone levels to plummet as one gets older, the AUA (American Urology Association) indicates that anything below 300ng of the hormone per deciliter of blood is a red flag that the hormone levels are low. While the only way to confirm the testosterone level is through a blood test, several symptoms point to the deficiency of this hormone in your body.