DEXA scan (body composition)

Dual-energy X-ray absorptiometry (DEXA) measures body composition and bone mineral density by directing two X-ray beams at different energy levels through tissue and quantifying differential attenuation; it partitions the body into lean mass, fat mass, and bone mineral content at regional and whole-body levels with high precision and low radiation (~1–10 µSv per scan). DEXA-derived appendicular lean mass index (ALMI = lean mass in kg of arms + legs / height in m²) is used in EWGSOP2 sarcopenia criteria and visceral adipose tissue (VAT) estimates are increasingly available on modern scanners. Serial DEXA measurements quantify muscle and fat changes from training, diet, and aging interventions; the method's main limitations include hydration sensitivity for lean-mass estimates and scanner-model variability.