Used to measure the calcium content of bones, a bone density scan is often ordered when a patient has risk factors for osteoporosis. In patients who have already been diagnosed with the condition, the study is used to determine if the prescribed treatment is effective.
The test is quick and painless, and no preparation is needed. Dual energy X-ray absorptiometry (DEXA) uses a movable scanner that passes over the lower spine and hip area and produces X-ray beams of two different energy levels. The patient lies on a table during the noninvasive procedure, which emits very low radiation levels and takes about 10 minutes.
Measurements from a bone density test are converted to a T-score, which is the level of bone density that is expected from a healthy 30-year-old adult of the same sex, and a Z-score, which compares the patient’s bone density to that of a healthy person of the same age, sex, and body size. A T-score of -2.5 or lower or a Z-score of -2 or lower could indicate osteoporosis.