Dual-Energy X-ray Absorptiometry (DXA) is the Primary Lab Test for Postmenopausal Women at Risk of Osteoporosis
Dual-energy X-ray absorptiometry (DXA) is the gold standard diagnostic test recommended for screening postmenopausal women at risk of osteoporosis, with bone density measurement at the femoral neck being the best predictor of hip fracture risk. 1, 2
Screening Recommendations by Age and Risk Factors
- All postmenopausal women aged 65 years and older should undergo routine DXA screening regardless of risk factors 2
- Postmenopausal women younger than 65 years should undergo DXA screening if they have additional risk factors for fracture 1
- For postmenopausal women aged 60-64 years with risk factors, the benefits of screening are comparable to routine screening in older women 1
- No routine screening is recommended for postmenopausal women younger than 60 years without risk factors 1
Key Risk Factors That Should Trigger Earlier Screening
- Low body weight (weight < 70 kg) is the single best predictor of low bone mineral density 1
- Previous fragility fracture at any age 2
- Long-term glucocorticoid therapy 2
- Medical conditions associated with bone loss (hyperparathyroidism, hypogonadism, chronic inflammatory diseases) 2
- Family history of osteoporosis (though less evidence supports this as a sole trigger for screening) 1
- No current use of estrogen therapy 1
DXA Testing Specifics
- Bone density measured at the femoral neck by DXA is the best predictor of hip fracture 1
- DXA results are expressed as T-scores, representing the standard deviation variance compared to a young-normal reference population 3
- BMD classification according to WHO criteria: 3
- Normal: T-score ≥ -1.0
- Osteopenia: T-score between -1.0 and -2.5
- Osteoporosis: T-score ≤ -2.5
Alternative Testing Methods
Other technologies for measuring peripheral bone sites include: 1
- Quantitative ultrasonography
- Radiographic absorptiometry
- Single-energy x-ray absorptiometry
- Peripheral dual-energy x-ray absorptiometry
- Peripheral quantitative computed tomography
Quantitative CT may be useful in patients with advanced degenerative bony changes in their spines 1
Trabecular bone score represents an emerging role for qualitative bone assessment 1
Follow-up Testing
- A minimum of 2 years is needed to reliably measure changes in bone mineral density 1
- For individuals with normal bone density or mild osteopenia, repeat DXA in 2-3 years 2
- For individuals with osteoporosis or on treatment, repeat DXA in 1-2 years to monitor treatment effectiveness 2
- Yield of repeated screening will be higher in older women, those with lower bone mineral density at baseline, and those with other risk factors for fracture 1
Clinical Considerations and Pitfalls
- The likelihood of being diagnosed with osteoporosis varies depending on the site and type of bone measurement test, number of sites tested, brand of densitometer used, and reference range 1
- African-American women on average have higher bone mineral density than white women at the same age and are thus less likely to benefit from screening 1
- Some patients with bone mineral density above the treatment threshold may still qualify for treatment based on vertebral fractures detected through vertebral fracture assessment scans 1
- Optimal use of DXA requires staff training and standard operating procedures that include quality controls for instrument maintenance, precision assessment, scan acquisition, analysis, interpretation, and reporting 3
Impact on Treatment Decisions
- BMD testing combined with assessment of clinical risk factors allows identification of patients who may benefit from pharmacologic therapy to reduce fracture risk 3
- The FRAX tool can be used to calculate 10-year fracture risk to guide treatment decisions 2
- Postmenopausal women with osteopenic BMD may warrant pharmacologic treatment if they have a FRAX-calculated 10-year probability of at least 3% for hip fracture or at least 20% for major osteoporotic fracture 4