Today, ten million Americans have osteoporosis and another 34 million exhibit the early stages of the condition. How are these people diagnosed. Osteoporosis is a condition where a person has reduced bone density, which is the amount of bone present in the skeletal structure. Most methods of diagnosing the condition do so by measuring bone density. Bone density grows during childhood and adolescence, reaching its peak mass around age 25. At this point, density remains steady for about ten years. After age 35, bone density will gradually drop at the rate of .3 to .5 percent each year. This is a normal part of the aging process and not the same as osteoporosis. One way to diagnosis osteoporosis is with a routine x-ray, since the bones in someone with the condition appear much thinner than healthy bones. Unfortunately, because x-rays can only detect large changes in bone density, they are not effective for diagnosing early-stage osteoporosis. A better way to diagnose the condition is with a more advanced scan known as a DXA. This short procedure uses a very small amount of radiation to measure the bone density of the hip and spine. The bone density of the patient is then compared to that of average young adults of the same sex and race who have peak, healthy bone mass. This comparison is written as a negative number called a T-score. A T-score greater than negative 1 is normal, or the same as a patient who has ideal bone mass. A score between negative one and negative 2.5 is classified as osteopenia, or "pre-osteoporosis," while osteoporosis is a number less than negative 2.5. Because it is impractical to test everyone for osteoporosis, doctors only perform DXAs on people with specific risk factors. The biggest risk factor for developing osteoporosis is being female. About 80 percent of people with the disease are women, largely due to the decrease in estrogen that occurs post-menopause. Women also have smaller skeletons, and experience bone loss earlier in life than men do. Advanced age is a second major risk factor. This is because bone mass begins decreasing more rapidly after age 65. As with many diseases, genetics play a role, too. A family history of osteoporosis and broken bones increases risk by up to fifty percent. Certain medications, like corticosteroids and chemotherapy drugs, can also increase the risk of bone loss.