Dual-energy X-ray absorptiometry (DXA) remains the most widely used imaging modality for assessing bone mineral density (BMD), playing a central role in diagnosing osteoporosis and osteopenia. Fragility fractures continue to impose a considerable burden on healthcare systems, so the importance of accurate diagnosis becomes more evident. DXA provides essential metrics such as BMD, T-scores and Z-scores, which are critical in guiding treatment and prevention strategies. However, the interpretation of DXA scans involves a range of complexities and potential pitfalls that demand a solid understanding from radiologists to ensure clinically reliable reports.
Diagnostic Criteria and Measurement Standards
DXA scans are typically performed at the lumbar spine and hips, with additional imaging at the distal radius when conventional regions are unsuitable. The method calculates site-specific BMD and derives T-scores and Z-scores to stratify fracture risk and determine bone health. The T-score compares a patient’s BMD to that of a healthy young adult, primarily used for postmenopausal women and men over 50. A T-score between -1.0 and -2.5 indicates osteopenia, while a score of -2.5 or below confirms osteoporosis. Conversely, the Z-score compares the patient’s BMD to age-, sex- and ethnicity-matched norms, making it the preferred index for younger populations and premenopausal women. A Z-score below -2.0 warrants further investigation for secondary causes of bone density loss.
Interpretation must account for potential inaccuracies introduced by underlying conditions, such as degenerative spinal changes, previous surgery or implanted devices, which can skew BMD readings. For example, scoliosis or severe osteoarthritis may artificially elevate lumbar spine scores. In such cases, alternative regions like the hip or forearm may offer more reliable diagnostic information. In patients with hyperparathyroidism or those unable to lie flat, imaging the one-third radius of the non-dominant arm is an accepted alternative approach.
Clinical Relevance and Risk Stratification
Osteoporosis is a prevalent and treatable cause of fragility fractures, commonly affecting the vertebral column, femur, radius, hip and tibia. The condition has a high societal cost, with tens of millions affected and billions spent on related care. As populations age, the prevalence of low bone mass is expected to rise, making early diagnosis and management increasingly essential. DXA is a validated method that enables clinicians to quantify fracture risk and initiate appropriate interventions.
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Tools such as the Fracture Risk Assessment Tool (FRAX) can complement DXA findings by incorporating clinical risk factors alongside BMD results to offer a ten-year fracture probability. This integrated approach enhances decision-making and supports targeted pharmacologic and lifestyle therapies. Because DXA uses low radiation doses and provides reproducible results, it is well suited to both initial diagnosis and long-term monitoring of bone health in at-risk individuals.
Interpretative Challenges and Pitfalls
Despite its advantages, DXA is not without interpretive challenges. The accuracy of the scan can be compromised by patient factors, anatomical abnormalities or technical limitations. Surgical hardware, degenerative disease and anatomical deformities such as scoliosis can lead to misleading results. Radiologists must be vigilant in recognising these issues and adjusting their evaluations accordingly. For example, a falsely elevated T-score due to vertebral degeneration might obscure the presence of osteopenia or osteoporosis.
Furthermore, the choice of anatomical region for measurement is critical. While the spine and hips are preferred, these may be unsuitable in certain clinical scenarios, requiring skilled judgment to determine when alternative sites are indicated. The lowest BMD value among the assessed regions is used to classify the overall diagnosis, emphasising the importance of comprehensive and region-specific analysis.
Another interpretative consideration is the selection of the appropriate score based on age and sex. Misapplication of T- or Z-scores can lead to incorrect diagnostic conclusions and inappropriate referrals or treatments. Clear understanding of guideline-recommended thresholds and population-specific norms is essential in producing accurate, clinically meaningful reports.
DXA remains the cornerstone of imaging in the evaluation of osteoporosis and osteopenia, offering critical data for diagnosis, risk assessment and treatment planning. However, successful interpretation requires not only familiarity with technical parameters but also a keen awareness of the common pitfalls and confounding factors that may influence scan results. Radiologists need to navigate anatomical variations, prior surgeries and degenerative changes while applying age-appropriate reference metrics. With growing demand for DXA imaging driven by demographic shifts, consistent adherence to best practices and guideline-based reporting is essential to optimise patient outcomes and reduce the burden of fragility fractures.
Source: RadioGraphics
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