DEXA Scan – Bone Density & Body Composition Test
DEXA (Dual-Energy X-Ray Absorptiometry) is an imaging technique used to measure bone mineral density and body composition. It is the gold standard for diagnosing osteoporosis.
Things worth knowing about "DEXA"
DEXA (Dual-Energy X-Ray Absorptiometry) is an imaging technique used to measure bone mineral density and body composition. It is the gold standard for diagnosing osteoporosis.
What is DEXA?
DEXA stands for Dual-Energy X-Ray Absorptiometry (also written as DXA). It is a non-invasive imaging technique that uses two X-ray beams at different energy levels to precisely measure bone mineral density (BMD) and body composition. DEXA is internationally recognized as the gold standard for diagnosing osteoporosis and monitoring bone health over time.
How Does a DEXA Scan Work?
During a DEXA scan, the patient lies comfortably on a padded table. A mechanical arm passes slowly over the body, emitting two low-dose X-ray beams at different energy levels. Because bone tissue and soft tissue absorb these beams differently, the scanner can accurately calculate bone mineral density as well as the proportions of fat mass, lean muscle mass, and bone mass – even for specific body regions.
- The scan is completely painless and typically takes between 10 and 20 minutes.
- Radiation exposure is extremely low – much less than a standard chest X-ray.
- No special preparation is required, and no contrast agents are used.
When is DEXA Used?
Bone Density Measurement (Osteoporosis Diagnosis)
The most common use of DEXA is in the diagnosis and monitoring of osteoporosis – a condition in which bone mass decreases, increasing the risk of fractures. The most common measurement sites are the lumbar spine and the femoral neck (hip). Results are reported as a T-score and a Z-score:
- T-score: Compares the patient's bone density to that of a healthy young adult. A T-score of −2.5 or lower indicates osteoporosis.
- Z-score: Compares the patient's bone density to the average for their age group.
Body Composition Analysis
DEXA is also widely used in sports medicine, nutritional medicine, and preventive health to analyze body composition in detail. It separately quantifies fat mass, lean mass (muscle), and bone mass – including regional breakdowns for the arms, legs, and trunk.
Indications for a DEXA Scan
- Suspected or confirmed osteoporosis
- Fracture following low-impact trauma (fragility fracture)
- Long-term use of corticosteroids or other bone-weakening medications
- Postmenopausal women with risk factors
- Men over 70 years of age with risk factors
- Conditions associated with increased bone loss (e.g., rheumatoid arthritis, malabsorption syndromes)
- Monitoring response to osteoporosis treatment
- Body composition assessment in sports and nutritional medicine
Interpreting DEXA Results
Bone mineral density is measured in g/cm² (grams per square centimeter). The T-score is the key value for clinical assessment:
- T-score ≥ −1.0: Normal bone density
- T-score between −1.0 and −2.5: Osteopenia (low bone mass, a precursor to osteoporosis)
- T-score ≤ −2.5: Osteoporosis
- T-score ≤ −2.5 with fracture: Severe osteoporosis
Results should always be interpreted within the broader clinical context, including additional risk factors and tools such as the FRAX score, which estimates the 10-year probability of a major fracture.
Advantages and Limitations of DEXA
Advantages
- Very low radiation exposure
- High precision and reproducibility
- Fast and non-invasive procedure
- Internationally standardized reference values
- Detailed body composition analysis capability
Limitations
- Osteoarthritis or vertebral deformities can distort spinal measurements
- Less accurate in patients with severe obesity
- Does not directly assess bone microstructure or quality
- Results may vary slightly between different manufacturers' devices
References
- World Health Organization (WHO): Assessment of fracture risk and its application to screening for postmenopausal osteoporosis. WHO Technical Report Series 843, Geneva, 1994.
- Kanis JA et al. – International Osteoporosis Foundation (IOF): FRAX and the assessment of fracture probability in men and women from the UK. Osteoporos Int. 2008;19(4):385–397.
- Blake GM, Fogelman I: The role of DXA bone density scans in the diagnosis and treatment of osteoporosis. Postgrad Med J. 2007;83(982):509–517.
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