A bone density scan, also known as a DEXA scan, is a quick and painless procedure used to measure the density of your bones. It’s a valuable tool in assessing bone health and is often used to diagnose osteoporosis or to assess your risk of developing it. The scan involves lying on your back on an X-ray table while a specific area of your body is scanned.
What Exactly is a DEXA Scan?
DEXA stands for Dual-energy X-ray absorptiometry. As the name suggests, a DEXA scan utilizes two different energy levels of X-rays to measure bone density. This method allows healthcare professionals to differentiate between bone and soft tissue, providing a precise measurement of bone mineral density (BMD). The procedure is generally performed by a radiographer, a specialist trained in taking X-ray images and other medical scans.
During a DEXA scan, you will lie on a padded, open X-ray table. It’s important to remain still throughout the scan to ensure the images are clear and not blurred. A large scanning arm is positioned above you, which will slowly move over your body. This arm emits a low dose of X-rays, significantly less than a standard chest X-ray, making it a safe procedure.
The primary areas assessed during a DEXA scan are typically the hip and lower spine. These are key areas to evaluate for osteoporosis as they are common sites for fractures related to bone density loss. However, depending on individual health concerns or limitations, other areas may be scanned as well. For instance, the forearm might be scanned in cases of certain medical conditions like hyperparathyroidism, or if the hip and spine cannot be scanned effectively.
As the scanning arm moves, the low-dose X-rays pass through your body. Some of these X-rays are absorbed by different types of tissue, including fat and bone. A detector within the scanning arm measures the amount of X-rays that pass through. Bones, being denser, absorb more X-rays compared to soft tissues. This difference in absorption is what allows the DEXA scan to accurately measure bone density. The information collected is then used to generate an image of the scanned area, which helps in determining bone density. The entire DEXA scan procedure usually takes between 10 to 20 minutes, and you can typically return home immediately after it’s completed.
Understanding Your DEXA Scan Results: T-scores and Z-scores
After your DEXA scan, the results will be analyzed and compared to two key benchmarks: the bone density of a young, healthy adult and the bone density of an average healthy adult of your age, gender, and ethnicity. These comparisons are presented as standard deviation (SD) scores, which indicate how much your bone density deviates from the expected norm.
The comparison to a young, healthy adult is known as a T-score. This score is crucial for diagnosing osteoporosis and assessing fracture risk in older adults. The World Health Organization (WHO) has established the following categories based on T-scores:
- Normal: A T-score above -1 SD. This indicates normal bone density.
- Osteopenia (Low Bone Density): A T-score between -1 and -2.5 SD. This signifies mildly reduced bone mineral density compared to peak bone mass, increasing the risk of osteoporosis.
- Osteoporosis: A T-score at or below -2.5 SD. This indicates osteoporosis, a condition characterized by significantly weakened bones and a high risk of fractures.
- Severe Osteoporosis: A T-score at or below -2.5 SD with the presence of one or more fragility fractures.
The comparison to someone of the same age, gender, and ethnicity is known as a Z-score. Z-scores are generally more relevant for children, premenopausal women, and younger men under 50. If your Z-score is below -2, it may indicate that your bone density is lower than expected for your age group, and further investigation into underlying causes might be necessary.
It’s important to remember that while DEXA scan results and BMD are strong indicators of bone strength, they are not the sole predictors of fractures. Other factors such as age, sex, history of falls, certain medical conditions, and lifestyle choices also play significant roles in fracture risk. Therefore, your doctor will consider your DEXA scan results in conjunction with your overall health profile and risk factors to determine if any treatment or lifestyle modifications are needed to protect your bone health.
In conclusion, a DEXA scan is a valuable and safe procedure for assessing bone density and identifying potential risks of osteoporosis. Understanding what a DEXA scan is, how it’s performed, and how to interpret the results empowers you to take proactive steps towards maintaining healthy bones. Always discuss your DEXA scan results and bone health concerns with your healthcare provider for personalized advice and management.
