Can FRAX Replace DEXA?
No, FRAX cannot replace DEXA for diagnosing osteoporosis—DEXA remains the gold standard and is required for definitive diagnosis, while FRAX serves as a complementary risk stratification tool to guide treatment decisions in patients with low bone mass. 1
Why DEXA Cannot Be Replaced
Diagnostic Authority
- DEXA is the only validated method for diagnosing osteoporosis using WHO criteria (T-score ≤ -2.5 at lumbar spine, femoral neck, total hip, or one-third radius). 1
- FRAX does not measure bone mineral density and therefore cannot be used to make a diagnosis of osteoporosis—it only estimates fracture probability. 1
- The WHO operational definition of osteoporosis requires either a T-score ≤ -2.5 on DEXA or a prior low-trauma major osteoporotic fracture. 1
Treatment Monitoring
- DEXA is essential for monitoring treatment effectiveness, with follow-up scans recommended after 2 years of therapy. 2
- FRAX scores change slowly over time and are not responsive enough to serve as a treatment target—change in FRAX score does not independently predict incident fractures. 3
- Only DEXA provides the precision needed to detect clinically significant changes in bone density (least significant change of 2.8-5.6% depending on precision error). 1
The Complementary Role of FRAX
When FRAX Adds Value
- FRAX is used in patients with osteopenia (T-score -1.0 to -2.4) to determine who needs pharmacologic treatment based on 10-year fracture probability. 1, 2
- Treatment is recommended when FRAX shows ≥3% 10-year hip fracture risk or ≥20% 10-year major osteoporotic fracture risk. 1, 2
- FRAX combined with DEXA BMD is more accurate than either alone for predicting fracture risk. 1
FRAX as a Screening Tool
- In specific populations, FRAX can help identify who needs DEXA scanning rather than replacing it entirely. 4, 5
- FRAX has high negative predictive value (94-100%) for ruling out patients who don't need DEXA, but low positive predictive value (0-16%) for identifying those who do. 4, 5
- This means a normal FRAX score can help avoid unnecessary DEXA scans, but an abnormal FRAX score still requires DEXA confirmation. 4, 5
Clinical Algorithm
For postmenopausal women ≥65 years:
- Perform DEXA as first-line screening—FRAX is not needed for initial diagnosis. 1
For postmenopausal women <65 years with risk factors:
- Calculate FRAX score first to determine if DEXA is warranted. 1
- If FRAX suggests low risk, DEXA may be deferred. 4, 5
- If FRAX suggests intermediate or high risk, proceed with DEXA for definitive diagnosis. 1
For patients with osteopenia on DEXA:
- Calculate FRAX using the femoral neck BMD to guide treatment decisions. 1, 2
- Treat if fracture probability exceeds thresholds (≥3% hip or ≥20% major osteoporotic fracture). 1, 2
Important Limitations
FRAX Shortcomings
- FRAX uses binary inputs (yes/no) for glucocorticoids and alcohol rather than quantified doses. 1
- Does not incorporate lumbar spine BMD, trabecular bone score, fall history, or frailty. 1
- Race-specific FRAX calculators may perpetuate disparities by always predicting lower risk in non-White populations with identical clinical profiles. 1
- Based on cohort data that is 30-40 years old with mortality estimates not updated since 2004. 1
DEXA Limitations in Specific Populations
- DEXA may overestimate BMD in patients with chronic kidney disease due to abdominal aortic calcifications—consider quantitative CT in these cases. 1
- In patients with extensive spinal degenerative disease, severe obesity (BMI >35), or extreme body heights, quantitative CT may be superior to DEXA. 1
The bottom line: DEXA and FRAX serve different but complementary purposes—DEXA diagnoses osteoporosis and monitors treatment, while FRAX stratifies fracture risk to guide treatment decisions in the osteopenic range. 1, 2