What is a DXA scan?
A DXA scan, short for dual x-ray absorptiometry, is a specialized non-invasive imaging technique designed to measure bone mineral density (BMD). DXA scans use extremely low-dose X-rays to assess the mass of bone tissue per bone area, most importantly in your spine and hip regions. The use of two energies allows the differentiation of bone from surrounding soft tissue, such as muscles and fat. This measurement calculates the density of your bones, which is the major way to determine their strength. Knowing your bone strength tells you how likely you are to break a bone during normal daily activities or minor accidents.
Why should women over 50 consider a DXA scan?
Hormone levels change throughout a woman’s life, but the major changes that occur during menopause put monitoring bone health at the forefront. For women at an average age of 50, the menopause-associated loss of estrogen production leads to a universal loss of bone mass and strength, although the rate of loss varies among individuals. During the first several years after menstruation stops, women can lose up to 10% of their bone mass (Ji, 2015). This process is silent – there are no symptoms.
Ultimately, loss of bone mass in mid-life increases your likelihood of developing osteopenia or osteoporosis, which may result in osteoporotic fractures. The best way to get ahead and stay ahead of bone loss and fractures is to assess your risk. The DXA scan can give you concrete information about your bone health.
What does a DXA scan measure?
Getting a DXA scan early after menstrual periods cease is the only way to determine what your starting bone density is (peak bone mass) and how likely you are to dip into an at-risk bone density range as bone loss progresses. If your bone density is low to begin with, you have options to help slow the subsequent bone loss.
Although bone loss is fastest in women at the time of menopause, bone loss progresses throughout the second half of life (Endocrine Society, 2022). The DXA scan is an essential tool to determine what can and should be done at any stage to maintain or improve bone density and reduce your likelihood of having bone breaks or fractures.
DXA scans and bone density scores
The DXA scan is the most well-studied and validated type of bone density test that reveals vital information about your bone health. The bone density test usually measures bone density in both your lower spine and your hip. The bone density results in these areas reflect the strength of bone throughout your skeleton. Results are usually presented as two important measurements: T-scores and Z-scores.
T-scores compare your bone density to that of a healthy young adult when bone density is at its peak. It highlights the degree of deviation from peak bone density. Negative T-scores indicate that bone density is lower than the average for young normal and negative T-scores can progress through the low bone mass range into osteoporosis. The T-score is the way osteoporosis is diagnosed and is the result that most doctors will report to you. We’ll go into how to interpret your T-score in more detail later in this article.
Z-scores, on the other hand, compare your bone density to others in your age group, offering insights into bone health compared to your peers. Since we all lose bone with age, the older you are, the more likely you might have a normal Z-score but still have low bone mass or osteoporosis by T-score.
Preparing for a DXA scan
Preparing for a DXA scan involves a few simple steps to ensure accurate results. One crucial aspect is to avoid taking calcium supplements on the day of the bone density scan, as they could interfere with the measurements. Additionally, you should wear comfortable clothing that doesn't have metal zippers, buttons, or buckles, as these can affect the scan's accuracy.
By following these basic guidelines, you can be confident that your DXA scan will provide reliable insights into your bone health.
DXA scan procedure
During the DXA scan, you'll lie still on a padded examination table while the DXA machine moves over your body. Rest assured, the procedure is non-invasive and painless and takes only about 10 minutes.
Unlike traditional X-rays, DXA scans expose you to minimal radiation, similar to the radiation exposure associated with a transcontinental flight.
How to interpret DXA scan results
When you receive the results of your DXA scan, your doctor will most likely focus on your T-scores. T-scores compare your bone density to that of a healthy young adult in the age range of 25-35, when bone density is at its peak.
DXA scans typically provide T-scores for two main regions of the body:
- Lumbar Spine: The lumbar spine is the lower part of the spine. This is a part of the skeleton which is most likely to show bone loss early after menopause.
- The Total Hip and the Femoral Neck of the Hip: The femoral neck is a part of the hip bone that connects the femur (thigh bone) to the hip joint. The total hip measurement includes the femoral neck and the outer part of the femur bone called the trochanter. Results for the total hip and femoral neck might be different and in the best centers, both results are reported. In addition, it is best if both hips can be measured simultaneously since results for right and left sides often vary.
These two areas are chosen because they are highly indicative of bone strength throughout the body. These results can tell you how likely you are to break the bones in your spine, hip, arm, pelvis, leg and other areas.
What does my T-score mean?
The T-score numbers are crucial indicators of your bone health status.
- Above -1: If your T-score is above -1, it's considered normal, indicating that your bone density is comparable to that of a healthy young adult.
- Between -1 and -2.5: If your T-score falls within this range, it suggests you have low bone density, also called osteopenia. This is a warning sign that your bone density is lower than normal, but not yet at the point of osteoporosis.
- Equal to or below -2.5: A T-score in this range indicates osteoporosis, a condition where bones have become significantly weaker and more susceptible to breaks or fractures.
These T-score values are critical guides in determining your bone health. It's important to note that the T-score alone doesn't predict when a fracture might occur, but it helps healthcare professionals evaluate the overall likelihood that this will occur.
Taking action based on DXA scan results
Once armed with the insights from your DXA scan results, taking proactive steps becomes crucial in maintaining and improving your bone health. Depending on your T-scores and overall bone density status, your healthcare provider will guide you through a personalized plan tailored to your needs. This plan may include an exercise prescription, medications, lifestyle changes and nutritional advice (or all of the above).
For those with normal T-scores, the focus might be on maintaining your current bone health through a diet rich in fruits and vegetables, calcium and vitamin D, along with engaging in weight-bearing and muscle-strengthening exercises to maintain bone strength.
If your T-scores indicate osteopenia or osteoporosis, your provider might recommend a more comprehensive approach. This could involve specific exercises to enhance bone density, medications to slow bone loss or improve bone density, and lifestyle and dietary adjustments.
Follow-up DXA scans might also be scheduled to track the effectiveness of your bone health strategies over time. In essence, the DXA scan results serve as a roadmap, guiding you and your healthcare team toward actions that will fortify your bones and minimize the risk of fractures as you navigate the path to better bone health.
How often should I get a DXA scan?
The timing of follow-up DXA scans after your initial assessment depends on a variety of factors, including your age, T-scores, overall bone health, and any ongoing treatments. In general, for individuals with normal bone density, a follow-up DXA scan might be recommended every 2 to 5 years. However, if your T-scores indicate osteopenia or osteoporosis, more frequent bone density scans might be advised to closely monitor changes and the effectiveness of your bone health interventions.
As you can see, a DXA (or DEXA) scan is a key component in the diagnosis, treatment and overall management of your bone health. Your healthcare provider will consider your unique circumstances when determining the results of your bone density scan and how to address those results. Osteoporosis is a chronic disease. Regular DXA scans can help you make adjustments to your bone health strategy promptly and track the progress of your bone health journey to ensure that your efforts to maintain or improve bone density are on the right track.