Interpreting T-Scores on a DEXA Scan
For a 75-year-old woman, the most critical part of a Dual-energy X-ray Absorptiometry (DEXA) scan report is the T-score. The T-score is a measurement that compares your bone mineral density to the average bone density of a healthy young adult (around age 30) of the same sex. For postmenopausal women, including those at age 75, the T-score is used to diagnose bone density status according to criteria established by the World Health Organization (WHO).
The T-score scale is interpreted as follows:
- Normal Bone Density: A T-score of -1.0 or higher. This indicates that your bone density is within the expected range and considered healthy.
- Low Bone Mass (Osteopenia): A T-score between -1.0 and -2.5. This means your bone density is lower than normal but has not yet reached the level of osteoporosis. For a woman of 75, having osteopenia is not uncommon, and it signals an increased risk for developing osteoporosis and fractures if left unaddressed.
- Osteoporosis: A T-score of -2.5 or lower. This diagnoses osteoporosis, indicating significantly reduced bone density and a high risk of fractures. According to a 2017–2018 survey, the prevalence of osteoporosis among women aged 65 and over was 27.1%, and the prevalence increases with age.
The Importance of the Lumbar Spine and Hip
A DEXA scan measures bone density at various skeletal sites, but the scores from the hip and spine are typically the most important for diagnosis. The diagnosis is made based on the lowest T-score from the measured sites. For example, if a 75-year-old woman has a T-score of -2.7 in her lumbar spine and -2.2 in her hip, the diagnosis is osteoporosis because the spine score meets the criteria, even though the hip score is in the osteopenia range.
Comparison of Bone Density Categories
| Characteristic | Normal Bone Density | Low Bone Mass (Osteopenia) | Osteoporosis |
|---|---|---|---|
| T-score Range | -1.0 and above | Between -1.0 and -2.5 | -2.5 or lower |
| Bone Strength | Healthy, strong bone structure | Weaker than normal, increased fracture risk | Significantly weakened and porous, high fracture risk |
| Fracture Risk | Low risk | Higher-than-average risk | Substantially increased risk, even from minor incidents |
| Clinical Status | Not a medical concern, but continued bone health is important | A warning sign that requires attention to prevent progression to osteoporosis | A disease requiring medical management and lifestyle adjustments to prevent fractures |
| Management | Maintain a healthy lifestyle with proper nutrition and exercise | Focus on lifestyle changes and potentially medication to prevent further loss | Requires medication, physical therapy, fall prevention, and lifestyle changes |
Factors Influencing Bone Density at Age 75
Several factors can influence a 75-year-old woman's bone density. The natural aging process is a primary cause of bone loss, but menopause significantly accelerates this decline due to the reduction of bone-protective estrogen. Other risk factors include a family history of osteoporosis, a small body frame, white or Asian ethnicity, and certain medical conditions like diabetes or rheumatoid arthritis. Lifestyle choices such as smoking, excessive alcohol consumption, and a diet low in calcium and vitamin D also play a major role.
Beyond the DEXA: FRAX and TBS
While the T-score from a DEXA scan is the standard for diagnosis, doctors may use other tools to get a more complete picture of fracture risk.
- FRAX Score: The Fracture Risk Assessment Tool (FRAX) estimates a person's 10-year probability of having a major osteoporotic fracture. It combines your T-score with other clinical risk factors such as age, BMI, prior fractures, and family history. This can help determine if treatment is necessary for someone with osteopenia.
- Trabecular Bone Score (TBS): This advanced software analysis, often included with a standard DEXA, measures bone structure and texture, offering a more nuanced understanding of bone quality than density alone. It is especially helpful because many fractures occur in individuals who have osteopenia, not just osteoporosis.
Conclusion
For a 75-year-old woman, normal bone density is defined by a T-score of -1.0 or higher from a DEXA scan. However, it is very common to have lower bone mass (osteopenia), and it becomes increasingly likely to have osteoporosis as you age. It is crucial to remember that bone health is dynamic. Even if a woman's T-score indicates low bone mass or osteoporosis, steps can be taken to mitigate the risks. A healthcare provider can recommend a comprehensive plan involving medication, exercise, and nutritional changes to slow bone loss, improve bone strength, and reduce the risk of fractures. Regular screening and proactive management are key to maintaining strong, healthy bones and an active lifestyle well into your senior years. For more information and resources on bone health, the Bone Health and Osteoporosis Foundation is a valuable resource.
