What's your t-score? Bone density scans for osteoporosis

We tend to associate broken bones with children roughhousing on playgrounds, but as we age our bones can turn brittle. Gradual bone loss with aging can lead to osteoporosis, a disease that thins and weakens bones and can result in broken hips, arms, and other fractures. Thanks to newer technology, finding out whether you have osteoporosis has become much easier.

Several technologies assess bone density. The most common is dual energy x-ray absorptiometry (DEXA): a machine sends x-rays through bone to calculate its density. The process is quick - about five minutes - and simple: you lie on a table while a scanner passes over your body.

Although DEXA can measure density anywhere in the body, it is usually aimed at the lumbar spine (lower back), the hip (a specific site near the hip joint), and the femoral neck (the top of the thighbone). And it does so with only one-tenth the radiation of a standard chest x-ray.

DEXA is considered the gold standard for osteoporosis screening. Ultrasound, which uses sound waves to gauge bone mineral density at the heel, shin, or finger, is also used at health fairs and in some medical offices.

Either test yields a number called a T-score, which shows how far your bone density sits from the average peak. The World Health Organization has set this classification system:

If your T-score is -1 or greater: your bone density is normal.

If your T-score is between -1 and -2.5: you have low bone density, known as osteopenia, but not osteoporosis.

If your T-score is -2.5 or less: you have osteoporosis, even if you have not yet broken a bone.