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A DXA scan is a type of medical test which is used to estimate the bone density of a patient. Such tests are useful for spotting early declines in bone density, which could be indicators of osteoporosis or other conditions. DXA scans are also called DEXA scans or bone densitometry tests, and they are typically recommended for the elderly, as they are at a higher risk of developing osteoporosis. In rare cases, such scans may also be used as diagnostic tools for younger patients.
DXA stands for Dual energy E-ray Absorptiometry. During the DXA scan, two x-rays with different levels of energy are aimed at the area of concern, and the absorption rate of the x-rays is used to calculate the concentration of minerals like calcium in the bone. Bones with a high concentration are deemed to be dense, at low risk of breaking, while bones with low density are porous, and potentially at risk of fracturing.
Typically, the DXA scan is performed on a bone which is at high risk of fracturing from osteoporosis, such as the hip. The test is usually very quick, and totally painless, and the amount of radiation involved is usually about a 10th of that experienced in a chest x-ray. After the scan, a radiologist will compute a T-Score and a Z-Score. The T-Score compares the density of the patient's bones to a healthy young adult of the same gender, while the Z-Score takes factors like age and ethnic identity into account.
Scores with negative numbers suggest that a patient has low bone mineral density (BMD). The scan will not, however, explain why the patient has low BMD. In some cases, this may be due to a condition like osteoporosis, but it can also be caused by a variety of medical conditions. When a DXA scan reveals low BMD, doctors typically recommend a medical workup to determine the root cause of the problem.
DXA scans are recommended for all women over age 65, as they are at the greatest risk for osteoporosis. Such scans may start as young as 60 for some patients, depending on a doctor's personal opinion. If a doctor recommends a DXA scan for you, you may want to be aware that many insurance companies do not cover these scans for women who are pre-menopausal.
There is an additional test available to check bone density. It does not use radiation but rather uses ultrasound of the heel. It is less expensive than DXA and since it does not use radiation, it has less risk associated with it.