Dual-Emission X-Ray Absorptiometry (DEXA ) is a means of measuring bone mineral density (BMD). Two x-ray beams with differing energy levels are aimed at patient' bones. When soft tissue absorption is subtracted out, the BMD can be determined from the absorption of each beam by bone. Dual-energy X-ray absorptiometry is the most widely used and most thoroughly studied bone density measurement technology. The DXA scan is typically used to diagnose and follow osteoporosis. It is not to be confused with the nuclear bone scan, which is sensitive to certain metabolic diseases of bone in which bones are attempting to heal from infections, fractures, or tumors.
DEXA scans are used primarily to evaluate bone mineral density. DXA scans can also be used to measure total body composition and fat content with a high degree of accuracy comparable to hydrostatic weighing with a few important caveats. However, it has been suggested that, while very accurately measuring minerals and lean soft tissue (LST), DXA may provide skewed results as a result of its method of indirectly calculating fat mass by subtracting it from the LST and/or body cell mass (BCM) that DXA actually and measures.
Woman over the age of 65 should get a DXA scan. At risk woman should consider getting a scan at age 60. 'At risk' includes many different clinical risk factors including: prior fragility fracture, use of glucocorticoids, heavy smoking, excess alcohol intake, rheumatoid arthritis, history of parental hip fracture, chronic renal and liver disease, chronic respiratory disease, long-term use of phenobarbitone or phenytoin, celiac disease, inflammatory bowel disease, and other risks. Clinical evidence on use of bone density scans in men is at present insufficient.