Recommended Initial Test for Bone Density Assessment in a 73-Year-Old Female
Dual-energy X-ray absorptiometry (DXA) is the recommended initial test to assess bone density in a 73-year-old female. 1
Rationale for DXA as First-Line Test
- DXA is the primary diagnostic modality recommended by the American College of Radiology (ACR) for screening women over 65 years of age for osteoporosis 1
- DXA provides accurate bone mineral density (BMD) measurements that have been shown to predict fracture risk with high reliability 1, 2
- DXA is considered the "gold standard" method for non-invasive diagnosis of osteoporosis with acceptable accuracy, good precision, and reproducibility 3, 4
- The World Health Organization (WHO) has established diagnostic criteria for osteoporosis based on DXA measurements 3
Specific Anatomic Sites for DXA Measurement
- Bone density measured at the femoral neck by DXA is the best predictor of hip fracture and comparable to forearm measurements for predicting fractures at other sites 1
- Standard DXA assessment typically includes measurement of both:
- Femoral neck BMD has shown the highest odds ratio for identifying subjects with vertebral fractures 5
Advantages of DXA Over Other Modalities
- Lower radiation exposure compared to other imaging techniques like Quantitative CT (QCT) 2
- Widespread availability and standardization 2
- Established reference databases for comparison and calculation of T-scores 3
- Better predictive ability for fracture risk than clinical risk factors alone 6
Interpretation of DXA Results
- Results are reported as T-scores, representing the number of standard deviations from the mean BMD of a young healthy reference population 3
- WHO diagnostic criteria based on T-scores:
- Normal: T-score greater than -1.0
- Osteopenia (low bone mass): T-score between -1.0 and -2.4
- Osteoporosis: T-score equal to or less than -2.5 1
Special Considerations
- Approximately 16% of lumbar spine scans may be unreadable due to degenerative changes, which are common in elderly patients 5
- In patients with advanced degenerative changes in the spine, Quantitative CT (QCT) may be a useful alternative 1
- Vertebral Fracture Assessment (VFA), which can be performed on some DXA machines, may provide additional fracture risk information 1
- Potential artifacts that can affect DXA measurements include osteoarthritis, previous fractures, and jewelry 2
Follow-up Recommendations
- Due to limitations in testing precision, a minimum of 2 years is typically needed to reliably measure changes in bone mineral density 1
- Follow-up DXA scans are recommended to:
- Assess the effectiveness of osteoporosis drug therapy
- Monitor medical conditions associated with abnormal BMD 1
By following these evidence-based recommendations for bone density assessment in a 73-year-old female, clinicians can accurately identify osteoporosis, estimate fracture risk, and monitor response to treatment.