Bone Density Score Converter
Interpret bone density T-scores and Z-scores with WHO diagnostic categories.
Understand what your DEXA scan results mean.
Enter a T-score or Z-score to see the WHO diagnosis and interpretation.
Osteopenia: T-score -1.0 to -2.5
Osteoporosis: T-score -2.5 and below
Understanding Bone Density Scores
Bone density is measured using a DEXA scan (Dual-energy X-ray Absorptiometry), which produces results as T-scores and Z-scores. These scores compare your bone mineral density (BMD) to reference populations and help doctors diagnose osteopenia and osteoporosis. Understanding these numbers empowers patients to discuss their bone health with their healthcare providers more effectively.
What is a T-Score?
A T-score compares your bone density to the average bone density of a healthy 30-year-old adult of the same sex. It is expressed as a standard deviation (SD) from the reference mean. The T-score is the primary measure used for diagnosing osteoporosis in postmenopausal women and men over age 50.
WHO Diagnostic Categories (Based on T-Score):
| T-Score Range | Diagnosis | Meaning |
|---|---|---|
| -1.0 and above | Normal | Bone density is within the healthy range |
| -1.0 to -2.5 | Osteopenia | Bone density is below normal but not yet osteoporosis |
| -2.5 and below | Osteoporosis | Significantly reduced bone density, high fracture risk |
| -2.5 and below with fracture | Severe Osteoporosis | Osteoporosis with one or more fragility fractures |
What is a Z-Score?
A Z-score compares your bone density to the average for someone of your same age, sex, weight, and ethnicity. It is more useful for premenopausal women, men under 50, and children. A Z-score below -2.0 is considered “below the expected range for age” and may indicate a secondary cause of bone loss.
The Relationship Between T-Score and Z-Score:
T-scores and Z-scores are related but use different reference populations. The approximate relationship depends on age and sex:
T-score ≈ Z-score + age-related bone loss offset
The offset varies by age group. For example, a healthy 70-year-old woman might have a Z-score of 0.0 (normal for age) but a T-score of -2.0 (osteopenia compared to a young adult) because bone density naturally decreases with age.
Bone Density Values (BMD in g/cm²):
Typical BMD values at the lumbar spine for women:
- Young adult mean: approximately 1.000 g/cm² (T-score = 0)
- Each standard deviation: approximately 0.120 g/cm²
- T-score of -2.5: approximately 0.700 g/cm²
Practical Examples:
- A 65-year-old woman with a hip T-score of -1.8 has osteopenia. Her bone density is below normal but has not yet reached the osteoporosis threshold of -2.5.
- A 45-year-old man with a Z-score of -2.3 should be evaluated for secondary causes of bone loss, such as vitamin D deficiency, thyroid disorders, or medication side effects.
- A postmenopausal woman with a spine T-score of -2.7 and a previous wrist fracture would be classified as having severe osteoporosis.
Tips:
- T-scores at different body sites (spine, hip, forearm) may differ. The lowest score is typically used for diagnosis.
- DEXA scan results should be compared over time using the same machine for consistency.
- Weight-bearing exercise, calcium, and vitamin D can help maintain bone density.
- Certain medications (corticosteroids, some seizure drugs) can accelerate bone loss.
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