A bone density scan, formally known as dual-energy X-ray absorptiometry (DEXA), is a non-invasive imaging test that measures the mineral content of your bones. This procedure uses a low dose of X-rays, typically focusing on the hip and spine, common sites for fragility fractures. The primary purpose is to evaluate bone mineral density (BMD), providing a baseline assessment of bone strength. The scan helps healthcare providers assess an individual’s risk for developing osteoporosis or low bone mass, known as osteopenia. Identifying these conditions early allows for interventions designed to prevent future bone breaks.
Initial Screening Guidelines
The decision to schedule a first or baseline bone density scan is based on age and specific clinical risk factors. Major medical organizations recommend that all women begin screening at age 65, and men start their first scan at age 70, regardless of other health history. These age thresholds reflect the point when age-related bone loss typically accelerates and the risk of fracture increases.
Screening may need to begin earlier if an individual has certain medical conditions or a history indicating elevated risk for bone loss. Risk factors include a previous fragility fracture (a bone fracture after a minor fall), low body weight, or taking specific medications such as long-term oral glucocorticoids (steroids). Other triggers involve conditions like rheumatoid arthritis, kidney disease, or premature menopause. For these individuals, a baseline scan may be warranted as early as age 50 to establish a reference point for future monitoring.
Determining Follow-Up Frequency
Once a baseline scan is complete, the frequency of subsequent DEXA scans is highly individualized and determined primarily by the initial T-score result. The T-score guides the monitoring schedule, as it reflects the current state of bone health. A one-size-fits-all approach is not used for follow-up testing, as bone density changes slowly in most people.
For individuals whose baseline scan shows normal bone density or only mild osteopenia (T-score better than -1.50), repeat testing can often be safely deferred for 10 to 15 years. This extended interval is possible because the rate of bone loss is minimal, making frequent scanning unnecessary for this low-risk category.
Patients with moderate osteopenia (T-score between -1.50 and -1.99) require closer monitoring. For this group, repeat scanning is commonly recommended every three to five years to track the rate of bone loss. If the initial T-score indicates advanced osteopenia, nearing the osteoporosis threshold (T-score -2.00 to -2.49), the monitoring interval shortens significantly to every one to two years.
The most frequent scanning schedule is reserved for patients diagnosed with osteoporosis or those undergoing treatment to improve bone density. In these cases, a follow-up scan is typically recommended annually or every two years. This close monitoring assesses the effectiveness of prescribed medication, such as bisphosphonates, and ensures the treatment is successfully preventing further bone loss.
Understanding Scan Results and Next Steps
The results of a bone density scan provide two standardized measurements: the T-score and the Z-score. The T-score is the primary diagnostic tool, comparing your bone mineral density to that of a healthy young adult at peak bone mass. This comparison classifies bone health into three categories: normal (T-score of -1.0 or higher), osteopenia (T-score between -1.0 and -2.5), and osteoporosis (T-score of -2.5 or lower).
The Z-score, in contrast, compares your bone density to the average density of others of the same age, sex, and ethnicity. A Z-score below -2.0 suggests that the bone loss may be due to factors other than typical aging, such as an underlying medical condition or a specific medication. The Z-score can prompt a deeper investigation into secondary causes of bone weakness.
The classification derived from the T-score dictates the subsequent action plan, ranging from preventative measures to medical intervention. A diagnosis of osteopenia often leads to recommendations for dietary adjustments, like increasing calcium and Vitamin D intake, and engaging in weight-bearing exercise. An osteoporosis diagnosis usually requires the initiation of prescription medication to reduce the risk of fracture, which defines the long-term monitoring schedule.