Normal Bone Mineral Density on DEXA Scan: WHO Criteria
According to WHO criteria, normal bone mineral density on a DEXA scan is defined as a T-score of -1.0 or higher (T-score ≥ -1.0). 1
Understanding the T-Score
The T-score represents how many standard deviations your bone density differs from the average bone density of a healthy 30-year-old adult of the same sex. Think of it as a comparison to peak bone mass:
- T-score ≥ -1.0 = Normal bone density - Your bones are within 1 standard deviation of peak bone mass
- T-score between -1.0 and -2.5 = Osteopenia (low bone mass) - Your bones are weaker than normal but not yet osteoporotic
- T-score ≤ -2.5 = Osteoporosis - Your bones are significantly weakened and at high fracture risk 1
What This Means Clinically
When your DEXA scan shows normal bone density (T-score ≥ -1.0), it indicates:
- Your bone strength is comparable to healthy young adults
- Your fracture risk is low based on bone density alone
- You typically don't need osteoporosis medication 1
- For low-risk individuals with normal baseline BMD, repeat testing is generally not needed for at least 3-16 years, as bone loss typically occurs at less than 1% per year 2
How DEXA Works
DEXA uses two different energy X-ray beams to measure bone mineral density, typically at two sites:
- Lumbar spine (L1-L4 vertebrae)
- Hip (femoral neck and total hip) 1
The test is quick (approximately 10 minutes), accurate (exceeds 90% at the hip), and uses minimal radiation—only 1/3 to 1/5 of a chest X-ray 2.
Important Caveats
A normal T-score doesn't tell the complete story about fracture risk. Other factors matter significantly:
- Age, sex, body weight, and height
- Family history of hip fracture
- Previous fragility fractures
- Smoking and alcohol use
- Long-term steroid use (>3 months)
- Conditions like rheumatoid arthritis 1
These additional risk factors are incorporated into tools like FRAX (Fracture Risk Assessment Tool) to provide a more comprehensive 10-year fracture probability 1.
The Z-Score: A Different Comparison
You may also see a Z-score on your DEXA report. This compares your bone density to others of your same age and sex, rather than to young healthy adults. Z-scores are not used to diagnose osteoporosis in adults but can help identify if bone loss is excessive for your age, suggesting secondary causes of bone loss that need investigation 1, 3.