DEXA (dual-energy X-ray absorptiometry) is a low-dose imaging test that measures bone mineral density and body composition by passing two X-ray beams of different energies through the body.
Because bone, fat, and lean tissue each absorb the two energy levels differently, the scanner separates them and quantifies each. Its original and most common clinical use is diagnosing osteoporosis and estimating fracture risk: results are reported as a T-score that compares a person's bone density against a healthy young-adult reference, with lower scores indicating weaker bone. The same scan also yields a detailed body-composition breakdown — total and regional fat mass, lean mass, and bone mass — which has made DEXA a reference standard used to validate other body-fat measurement methods.
A whole-body DEXA scan takes only a few minutes and delivers a radiation dose far smaller than a standard X-ray or CT. In clinical medicine it guides screening and treatment for bone loss; in fitness and longevity contexts it is used to track changes in muscle and fat over time with a precision that scales, calipers, and bioelectrical impedance cannot match.