What is the accuracy of bone densitometry using ultrasound?

Accuracy of Bone Densitometry Using Ultrasound

Quantitative ultrasound (QUS) of the calcaneus can predict fractures effectively but cannot replace DXA as the diagnostic standard for osteoporosis due to variable sensitivity and specificity. 1

Comparison Between QUS and DXA

Diagnostic Accuracy

• QUS of the calcaneus shows moderate correlation with DXA measurements, with correlation coefficients ranging from 0.38 to 0.42 when compared to total-body BMD 2
• Sensitivity of QUS ranges from 79% to 93%, while specificity varies widely from 28% to 90% 3
• No standardized QUS cutoff value exists at which both sensitivity and specificity are high for identifying individuals with T-scores ≤ -2.5 on DXA 1
• A meta-analysis of 25 studies showed wide variation in sensitivity and specificity when using QUS to identify osteoporosis as defined by DXA 1

Fracture Prediction

• Recent studies demonstrate that QUS of the calcaneus can predict fractures as effectively as DXA in postmenopausal women and men 1
• In some studies, QUS has been shown to be more effective than DXA at predicting vertebral fracture risk in specific populations 2

Limitations of QUS for Osteoporosis Diagnosis

Standardization Issues

• QUS measurements are not interchangeable with DXA measurements 1
• The WHO classification system for osteoporosis (T-score ≤ -2.5) cannot be directly applied to QUS results 1, 4
• Different studies have proposed different threshold values for QUS, ranging from T-scores of -1.7 to -3.65, to achieve diagnostic equivalence with DXA 3

Clinical Application Challenges

• All clinical trials evaluating drug therapies for osteoporosis use DXA measurements as inclusion criteria, limiting the clinical utility of QUS alone 1
• For QUS to be clinically useful, a standardized method for converting QUS results to the DXA scale would need to be developed 1
• The American College of Radiology does not support the current use of QUS as a standalone screening tool in patients suspected of having osteoporosis 1

Potential Benefits of QUS

Practical Advantages

• QUS is less expensive than DXA, does not involve radiation, and can be feasibly implemented in primary care settings 1, 2
• High patient acceptance and ease of use make QUS potentially suitable for community screening 5, 6
• May be particularly valuable in resource-limited settings where DXA is not available 2

Cost-Effectiveness Considerations

• Using QUS as a pre-screen for DXA referral has been investigated but showed no cost advantage in a study of women with low trauma Colles' fractures (£78 vs £77 per osteoporotic subject identified) 7
• QUS would only be cost-effective as a pre-screen if performed at a substantially lower cost 7

Current Recommendations

• DXA remains the gold standard for diagnosing osteoporosis and guiding treatment decisions 1, 4
• QUS should be regarded as a secondary tool to DXA for screening purposes 1
• QUS may be useful as an additional assessment tool, particularly in settings where DXA is unavailable 2
• When using QUS, practitioners should be aware that the WHO diagnostic criteria for osteoporosis cannot be directly applied 1, 4

Conclusion

While QUS demonstrates value in predicting fracture risk and offers practical advantages such as lower cost and absence of radiation, its variable accuracy in diagnosing osteoporosis compared to DXA limits its use as a standalone diagnostic tool. The lack of standardized cutoff values that provide both high sensitivity and specificity remains a significant limitation for clinical application.