What does a DXA scan measure?

A DXA (dual-energy X-ray absorptiometry) scan is the most common densitometry test used to measure bone mineral density at key sites such as the lumbar spine, hip, and sometimes the forearm. DXA provides precise numeric BMD values and derives standardized scores that allow comparison with young-adult or age-matched reference populations. Clinicians use DXA results to inform diagnosis and monitor changes over time. Because DXA is low-radiation, it is suitable for repeat screening and assessment in populations at risk of osteoporosis or fracture.

This article is for informational purposes only and should not be considered medical advice. Please consult a qualified healthcare professional for personalized guidance and treatment.

Understanding T-scores and Z-scores

T-scores and Z-scores are standardized metrics reported from densitometry imaging. A T-score compares an adult’s BMD to a healthy young-adult reference and helps classify bone status for osteoporosis diagnosis. A Z-score compares BMD to an age- and sex-matched population and can highlight when results are unusually low for that age. Both scores are useful in clinical risk assessment but have different diagnostic roles. Interpreting these scores alongside clinical factors such as menopause status, medication use, and other conditions improves diagnostic accuracy.

How is fracture risk estimated?

Fracture risk estimation combines bone mineral results with clinical risk factors such as age, prior fracture, family history, smoking, alcohol use, and glucocorticoid exposure. Tools that integrate DXA-derived values with clinical inputs provide a probabilistic fracture risk over a set period, often ten years. BMD is an important predictor, but bone quality, fall risk, and comorbidities also influence fracture outcomes. Communicating results in terms of relative and absolute fracture risk helps patients and clinicians weigh prevention or treatment options and prioritize interventions like fall prevention or bone-targeted therapies.

When is bone screening recommended?

Bone screening is commonly recommended for older adults and for people with specific risk factors: long-term steroid use, prior fragility fractures, conditions that affect bone metabolism, and values such as early menopause. Screening frequency depends on initial results and risk changes; repeat DXA might be advised every one to three years in cases of rapid bone loss or after starting treatment, and less often when bone density is stable. Local services and primary care providers can advise on appropriate screening intervals based on individual risk and clinical guidelines.

Calcium, vitamin D, and prevention

Nutritional factors such as adequate dietary calcium and vitamin D status support bone health but do not replace the diagnostic role of imaging. Preventive strategies for people with low bone density include lifestyle measures—regular weight-bearing exercise, smoking cessation, limiting alcohol intake—and ensuring recommended calcium and vitamin D intake. Supplementation decisions should be individualized, accounting for dietary intake, laboratory values, and potential interactions. Prevention efforts also focus on reducing fall risk through home safety, vision checks, and balance training, which complement bone-specific interventions.

Role of imaging in diagnosis and management

Beyond DXA, other imaging techniques and tests may contribute to diagnosis or secondary evaluation. Vertebral imaging can detect asymptomatic fractures that influence diagnosis and treatment choice. Quantitative CT provides three-dimensional assessment and trabecular vs cortical bone evaluation in selected cases but involves higher radiation and cost. Laboratory tests assess calcium metabolism, vitamin D levels, and secondary causes of bone loss. Together, imaging and targeted testing inform a comprehensive assessment, guide diagnosis of osteoporosis or other bone conditions, and help tailor prevention and treatment strategies.

In summary, bone mineral results provide numeric measures that must be interpreted in clinical context. DXA-derived BMD, T-scores, and Z-scores are central to assessment, while fracture risk estimation combines those numbers with health history and lifestyle factors. Imaging and laboratory evaluation together guide diagnosis, monitoring, and prevention approaches for people at risk of osteoporosis and fracture.