The Role of DEXA Scans and T-Scores
Bone mineral density (BMD) is most accurately measured using a dual-energy X-ray absorptiometry (DEXA) scan, a quick and painless procedure. The results are reported as a T-score, which compares your BMD to that of a healthy young adult of the same sex. This standardized score is the primary diagnostic tool for determining your bone health status.
Understanding Your T-Score
Your T-score places your bone density into one of three categories defined by the World Health Organization (WHO):
- A T-score of -1.0 or higher is considered normal bone density.
- A T-score between -1.0 and -2.5 indicates low bone mass, or osteopenia.
- A T-score of -2.5 or lower is diagnostic for osteoporosis, signifying a high risk of fracture.
A low T-score indicates that your bones are weaker than normal, with the fracture risk increasing as the T-score becomes more negative. For example, a person with a T-score of -1 has double the risk of fracture compared to someone with a normal T-score. However, a T-score is only one part of a complete risk assessment.
Low Bone Mass (Osteopenia)
While osteopenia isn't as severe as osteoporosis, it still represents an elevated fracture risk. For individuals with osteopenia, other clinical risk factors are critical for determining if they are at high risk. A person with osteopenia who has additional risk factors, such as a prior fracture or specific medical conditions, might be recommended for treatment to prevent further bone loss.
Beyond the T-Score: Additional High-Risk Factors
A low DEXA scan score is not the only indicator of high-risk bone density. Several other independent factors play a significant role in assessing an individual's total fracture risk.
Medical Conditions and Lifestyle
- Prior Fractures: A previous fragility fracture—a fracture from minor trauma, like a fall from a standing height—is one of the strongest indicators of high risk, regardless of your DEXA results. A history of multiple fractures is an even more serious sign.
- Age and Gender: Bone loss naturally accelerates with age. Postmenopausal women, especially those over 65, and men over 70 are at significantly higher risk.
- Body Weight: Low body weight (under 127 pounds) or a low BMI is a risk factor, as smaller frames have less bone mass to start with.
- Chronic Diseases: Several health conditions can weaken bones, including rheumatoid arthritis, kidney disease, liver disease, chronic obstructive pulmonary disease (COPD), hyperthyroidism, and anorexia nervosa.
- Genetics: A strong family history of osteoporosis, particularly a parent with a hip fracture, increases your risk.
- Lifestyle Choices: Smoking, excessive alcohol consumption (more than two drinks per day), and a sedentary lifestyle contribute to bone loss.
Medication-Induced Bone Loss
Certain long-term medications are known to weaken bones and increase the risk of osteoporosis. These include:
- Oral corticosteroids (e.g., prednisone), commonly used for arthritis or asthma.
- Thyroid hormone replacement medication, especially at high doses.
- Immunosuppressant drugs.
- Certain seizure medications.
- Proton pump inhibitors (PPIs) for acid reflux.
If you are on any of these medications long-term, your doctor may recommend earlier bone density screening to monitor your bone health.
The FRAX Tool: A Comprehensive Risk Assessment
For a more complete picture of fracture risk, doctors often use the Fracture Risk Assessment Tool (FRAX). This tool combines your bone density score with other clinical risk factors to calculate the 10-year probability of experiencing a major osteoporotic fracture.
How FRAX Works
The FRAX score considers factors such as age, gender, BMI, family history of fracture, prior fracture history, and use of specific medications. The algorithm provides a personalized risk assessment that helps determine the best course of action.
High Risk Defined by FRAX
Different countries have varying guidelines for interpreting FRAX scores, but generally, a high risk of fracture warrants treatment even if the T-score is not in the osteoporosis range. For example, some Canadian guidelines classify individuals over 50 with a history of hip or vertebral fractures as high risk regardless of their BMD.
Comparing Bone Density Risk Levels
| Classification | T-Score Range | Associated Fracture Risk |
|---|---|---|
| Normal | -1.0 and above | Low risk compared to the healthy young adult mean. |
| Osteopenia (Low Bone Mass) | Between -1.0 and -2.5 | Intermediate risk. Can be elevated to high risk with additional clinical factors. |
| Osteoporosis | -2.5 or lower | High risk, often requiring treatment to prevent fractures. |
| Severe Osteoporosis | -2.5 or lower + fragility fracture | Very high risk; previous fracture confirms severe bone weakness. |
Conclusion
High risk for bone density extends beyond a single number. While a T-score of -2.5 or lower is a definitive high-risk marker for osteoporosis, a high FRAX score or a history of fragility fractures can also signal a high-risk situation, even with a better T-score. It is important to have a comprehensive discussion with your healthcare provider, taking into account all personal and medical risk factors, to determine the most effective strategy for protecting your bone health.
For more information on bone density diagnosis and risk factors, visit the official website of the Bone Health and Osteoporosis Foundation.
