The Testosterone Test measures the level of testosterone in your blood. In men, testosterone is the hormone that regulates sex drive, builds bone mass, regulates body fat distribution, maintains muscle mass and strength, and is essential for the sperm production. Low levels of testosterone are associated with aging and common medical conditions including diabetes, high blood pressure, and obesity. Abnormal levels of testosterone in the blood may cause changes in health and physical appearance. If your results are not within normal range, it is important to consult with your physician to discuss next steps.