What Is a DEXA Scan and How Does It Work?
A dual-energy X-ray absorptiometry, or DEXA, scan is a safe, painless, and fast imaging test that measures bone mineral density (BMD). The scan directs two X-ray beams at the bones, most commonly the hip and spine, to calculate how much bone mineral is present in grams per square centimeter (g/cm²). The resulting value is then compared to established standards to produce a T-score and a Z-score, which help determine the health of your bones.
Deciphering Your T-Score
For post-menopausal women and men aged 50 and over, the T-score is the standard measurement used to diagnose bone density conditions. This score compares your bone density to that of a healthy young adult at peak bone mass. It is the most important number in determining if you have normal bone density, low bone mass (osteopenia), or osteoporosis.
Normal Bone Density
A T-score of -1.0 or higher is considered normal bone density. This indicates that your bone mineral density is healthy and within the expected range for someone at their peak bone mass. Regular exercise, a balanced diet rich in calcium and vitamin D, and other healthy lifestyle choices are recommended to maintain this status.
Low Bone Mass (Osteopenia)
A T-score that falls between -1.0 and -2.5 is classified as low bone mass, a condition also known as osteopenia. While not yet osteoporosis, it signifies that your bones are weaker than normal and you are at an increased risk of fracture. A doctor may recommend lifestyle changes and, depending on your fracture risk factors, may discuss treatment options.
Diagnosing Osteoporosis
For adults aged 50 and over, what level of DEXA scan indicates osteoporosis? The answer is a T-score of -2.5 or lower. This confirms a diagnosis of osteoporosis, a disease that makes bones fragile and more likely to break. The diagnosis is made based on the lowest T-score recorded from any of the measured skeletal sites, such as the lumbar spine, total hip, or femoral neck. A diagnosis of severe (established) osteoporosis is made when a T-score of -2.5 or lower is accompanied by one or more fragility fractures.
Understanding Your Z-Score
In addition to the T-score, your DEXA scan report may also include a Z-score. The Z-score compares your bone density to the average for people of your same age, gender, weight, and ethnicity. For pre-menopausal women and younger men, the Z-score is the primary measure used. A Z-score below -2.0 is considered low for age and may signal that other medical conditions or factors could be contributing to bone loss.
Beyond the Scan: Considering Fracture Risk (FRAX)
While the T-score is a critical diagnostic tool, it is not the only factor healthcare providers consider. For individuals with osteopenia, the FRAX (Fracture Risk Assessment Tool) may be used to estimate a person's 10-year probability of a major osteoporotic fracture. This tool combines the femoral neck BMD from the DEXA scan with other clinical risk factors, such as age, BMI, family history of fractures, and smoking status, to provide a more personalized fracture risk assessment.
T-Score Classification Summary
| T-Score Range | Classification | Who It Applies To |
|---|---|---|
| -1.0 and above | Normal bone density | Post-menopausal women and men 50+ |
| Between -1.0 and -2.5 | Low bone mass (Osteopenia) | Post-menopausal women and men 50+ |
| -2.5 and below | Osteoporosis | Post-menopausal women and men 50+ |
| -2.0 and below (warning) | Low bone mass for age | Pre-menopausal women and men under 50 |
Next Steps After a DEXA Scan
Once you and your healthcare provider have reviewed your DEXA scan results, a plan of action can be developed. For a normal T-score, recommendations will focus on prevention through maintaining a healthy lifestyle. For osteopenia, the focus will be on slowing bone loss and minimizing fracture risk, which may include further testing. For an osteoporosis diagnosis, treatment strategies may include medication and more intensive lifestyle interventions aimed at strengthening bones and reducing fracture risk. For comprehensive information on managing bone health, including diagnostic and treatment options, visit the official website of the Hospital for Special Surgery.
Conclusion
Answering what level of DEXA scan indicates osteoporosis? is a key part of understanding your bone health. A T-score of -2.5 or below signals a need for intervention to prevent serious fractures. The DEXA scan is a powerful tool, but it's most effective when its results are interpreted within the context of your overall health and risk factors. By taking proactive steps based on your scan and your doctor's recommendations, you can take control of your bone health and contribute to healthy aging.
