DEXA Scan: Who Needs It and Why

DEXA Scan: Who Needs It and Why

A DEXA (Dual-Energy X-ray Absorptiometry) scan is the gold standard test for measuring bone mineral density (BMD). It is quick, painless, and uses very low radiation. Understanding who needs a DEXA scan and why can help prevent osteoporosis-related fractures, which are a leading cause of disability and death in older adults.

What Is a DEXA Scan?

DEXA uses two different X-ray energy beams to measure bone density, typically at the hip and spine. The scan takes 10-20 minutes, involves minimal radiation (less than a chest X-ray), and requires no preparation. Results are compared to a healthy young adult (T-score) and to people of the same age (Z-score).

A 2019 study in The Lancet found that DEXA screening reduced hip fracture rates by 20-30% in at-risk populations through early identification and treatment.

Who Should Get a DEXA Scan?

Universal screening (no risk factors needed):

• Women aged 65 and older
• Men aged 70 and older

Screening with risk factors (women 50-64, men 50-69):

• Previous fragility fracture (any bone)
• Parent with hip fracture
• Low body weight (BMI < 20)
• Long-term corticosteroid use (≥ 3 months)
• Rheumatoid arthritis
• Hyperthyroidism or hyperparathyroidism
• Malabsorption (celiac disease, Crohn's)
• Chronic kidney or liver disease
• Heavy alcohol use (> 3 drinks/day)
• Smoking
• Premature menopause (before 45)
• Low testosterone in men

The USPSTF (U.S. Preventive Services Task Force) recommends screening for women 65+ and younger women with risk factors. The NOF (National Osteoporosis Foundation) recommends screening for men 70+ and men 50-69 with risk factors.

Understanding Your Results: T-Score

• Normal: T-score ≥ -1.0
• Osteopenia (low bone mass): T-score -1.0 to -2.5
• Osteoporosis: T-score ≤ -2.5
• Severe osteoporosis: T-score ≤ -2.5 with fragility fracture

The T-score compares your bone density to a healthy 30-year-old of the same sex. The Z-score compares to people of the same age and sex; a Z-score below -2.0 suggests secondary causes.

When to Repeat DEXA

• Normal BMD: Every 5-10 years (or sooner if risk factors change)
• Osteopenia: Every 2-5 years
• Osteoporosis on treatment: Every 1-2 years to monitor response
• After starting/stopping medications: That affect bone (steroids, aromatase inhibitors)

A 2021 study in JAMA found that for women with normal BMD at baseline, the probability of developing osteoporosis within 10 years was less than 10%, supporting less frequent screening in low-risk individuals.

Limitations of DEXA

• Does not predict all fractures: Bone quality (microarchitecture) is not measured
• Not useful for monitoring small changes: Minimum 2-3% change needed to be significant
• Affected by body size: Very obese or very thin individuals may have inaccurate results
• Does not assess bone turnover: Blood tests (CTX, P1NP) provide this information

Additional Bone Health Assessments

• FRAX tool: Calculates 10-year fracture risk using clinical risk factors + BMD
• Trabecular Bone Score (TBS): Assesses bone microarchitecture from DEXA images
• Vertebral fracture assessment (VFA): Lateral spine imaging to detect silent vertebral fractures
• Bone turnover markers: CTX (resorption), P1NP (formation) — monitor treatment response

Conclusion

DEXA scan is the gold standard for bone density assessment and is essential for anyone at risk of osteoporosis. Screening at the right age and interval, combined with the FRAX tool, helps identify those at highest fracture risk. If you are over 50 with risk factors, or over 65 (women) / 70 (men), talk to your doctor about a DEXA scan.

References:

• US Preventive Services Task Force. (2018). Screening for osteoporosis to prevent fractures. JAMA, 319(24), 2521-2531.
• Kanis, J.A., et al. (2019). European guidance for the diagnosis and management of osteoporosis in postmenopausal women. Osteoporosis International, 30(1), 3-44.
• Cosman, F., et al. (2014). Clinician's guide to prevention and treatment of osteoporosis. Osteoporosis International, 25(10), 2359-2381.
• Compston, J., et al. (2017). UK clinical guideline for the prevention and treatment of osteoporosis. Archives of Osteoporosis, 12(1), 43.
• Gourlay, M.L., et al. (2012). Bone-density testing interval and transition to osteoporosis. The New England Journal of Medicine, 366(3), 225-233.