DXAscanning

DXAscanning refers to dual-energy X-ray absorptiometry (DXA or DEXA) scanning, a medical imaging technique used primarily to measure bone mineral density (BMD) and assess fracture risk. It is widely regarded as the clinical standard for diagnosing osteopenia and osteoporosis.

The technology uses two X-ray beams at different energy levels to estimate areal BMD (g/cm2) by measuring how much each beam is attenuated by bone and soft tissue. Common measurement sites are the lumbar spine and proximal femur (hip); the forearm is used when spine or hip assessment is not possible. Modern DXA systems can also estimate body composition, including lean mass and fat mass distribution.

DXA scans are noninvasive, quick (typically 10–20 minutes), and involve very low radiation exposure. Results are reported as T-scores and Z-scores. A T-score compares the patient’s BMD to a young healthy adult reference: a T-score of −1.0 or higher is normal, between −1.0 and −2.5 indicates low bone mass (osteopenia), and −2.5 or lower is diagnostic of osteoporosis. Clinical interpretation considers age, sex, prior fractures, and other risk factors.

Limitations include reduced accuracy in the presence of spinal degeneration, vascular calcifications, metal implants, or obesity. Serial monitoring is most reliable when performed on the same machine and site; typical reassessment intervals range from 1 to 2 years depending on clinical context. DXA is contraindicated during pregnancy due to ionizing radiation.

Alternatives and complementary tests include quantitative computed tomography (QCT), peripheral ultrasound, and biochemical markers of bone turnover. Clinical management decisions should be based on DXA results integrated with patient history and guideline-based risk assessment.