Normal Limits on DEXA Scan
A DEXA scan T-score of ≥ -1.0 represents normal bone mineral density (BMD) according to World Health Organization criteria. 1
WHO Diagnostic Classification
The interpretation of DEXA results is based on T-scores, which compare an individual's BMD to that of a young healthy adult reference population, expressed in standard deviations:
- Normal BMD: T-score ≥ -1.0 1
- Osteopenia (Low Bone Mass): T-score between -1.0 and -2.5 1
- Osteoporosis: T-score ≤ -2.5 1
Measurement Sites and Diagnostic Approach
Diagnostic classification is based on the lowest T-score at any of the recommended DXA measurement sites, which include the lumbar spine (L1-L4), femoral neck, total hip, or one-third (33%) radius. 1
The femoral neck is designated as the reference site for epidemiological studies, though all recommended sites are valid for clinical diagnosis. 1
Age-Specific Considerations
Adults (Postmenopausal Women and Men ≥50 Years)
- Use T-scores for interpretation 1
- Apply the WHO classification thresholds listed above 1
- T-score calculation uses young adult Caucasian female normative reference database for both women and men 1
Younger Populations (Children, Adolescents, Premenopausal Women, Men <50 Years)
Use Z-scores instead of T-scores for interpretation in these populations. 1
- Z-score ≤ -2.0: Defined as "bone mineral density below the expected range for age" 1
- The terms "osteopenia" or "osteoporosis" should not be used to classify BMD measurements in these younger patients according to ISCD recommendations 1
- However, IOF recommends that a T-score ≤ -2.5 in premenopausal women and men younger than 50 years may be diagnostic of osteoporosis when skeletal fragility is present 1
Important Clinical Caveats
A diagnosis of osteoporosis may be made even with normal BMD (T-score ≥ -1.0) if a prior low-trauma major osteoporotic fracture has occurred (hip, spine, forearm, humerus, pelvis), as pragmatically proposed by EANM, ASBMR, and CSEM. 1
Caution is advised when performing forearm measurements, as this is not the most relevant site for fracture risk assessment. 1
For serial monitoring, repeat measurements should be conducted on the same DXA system with identical positioning and analysis protocols to ensure accurate comparison. 1
The radiation exposure from DEXA is negligible—less than one chest X-ray—posing essentially no meaningful health risk to patients. 2