Ask An Expert: DEXA Scan

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Ask An Expert: DEXA Scan

Question:

Is a DEXA scan the same as a bone density scan?

Answer:

A DEXA scan (now often called a DXA scan) is the most widely used test to measure bone mineral density (BMD). There are other methods of measuring BMD, including smaller "peripheral DEXA" scans done in doctors' offices and malls, scans that use photon energy, special computer tomography (CT) scans that measure BMD, and ultrasound bone density tests. However, these are not widely used at this time because of limitations compared to DEXA scans.

DEXA stands for "dual-energy X-ray absorptiometry." DEXA scanners produce two different X-ray beams, one high energy and one low energy. The X-ray energy that passes through the bone is measured, and calculations are then made to arrive at a bone density measurement. The amount of radiation used for the test is extremely small — much less than that used in a chest X-ray.

The strength of a bone generally depends on the amount of bone material present — the bone mineral density. A DEXA scan measures bone density in order to estimate bone strength. Studies have shown a strong connection between a person's risk of fractures (broken bones) and the DEXA-measured BMD. A DEXA scan can also used to monitor a person's response to treatment of thin bones (osteoporosis).

DEXA bone density testing is the most accurate method widely available for the diagnosis of osteoporosis. Usually, DEXA scans focus on the bone density of the hip and the spine, but this usually is a good measure of bone density in other bones. A DEXA scan is painless, accurate and takes only about 15 minutes to complete.

A "bone density scan" or DEXA scan should not be confused with a bone scan, which is a test using radioactive material to look for tumors, infections and fractures.

Diana Post, M.D., is an assistant professor of medicine at Harvard Medical School and a member of the Department of Medicine at Brigham and Women's Hospital.

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Last updated:	January 24, 2007

Medical content reviewed by the Faculty of the Harvard Medical School. Harvard Health Publications, Copyright © 2007 by President and Fellows of Harvard College. All rights reserved. Used with permission of StayWell.

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