Which test is used to measure bone density in osteoporosis evaluation?

• A. MRI scan
• B. CT scan
• C. DEXA bone density scan
• D. Ultrasound of the calcaneus

Answer: (C)

Measuring bone mineral density to evaluate osteoporosis is best done with a DEXA scan. This dual-energy X-ray absorptiometry test uses low-dose X-rays to quantify bone density at key sites, typically the spine and hip, and it yields a T-score and Z-score to classify bone health. A T-score of -2.5 or lower defines osteoporosis, while -1.0 to -2.5 indicates osteopenia, guiding treatment decisions and fracture risk assessment. DEXA is the standard because it directly measures density with high accuracy, is highly reproducible over time, and involves only a small amount of radiation, making it ideal for screening and monitoring therapy. Other imaging modalities can visualize bone or structure, but they do not provide the reliable density measurement needed for diagnosing osteoporosis; MRI and CT focus more on anatomy and morphology, and while quantitative CT exists, it’s not as widely used as DEXA due to higher radiation and cost. Ultrasound of the calcaneus has limited accuracy and is not the primary method for diagnosing osteoporosis.