what is a dual energy xray absorptiometry

3 min read 14-03-2025

what is a dual energy xray absorptiometry

Dual-energy X-ray absorptiometry (DXA or DEXA) is a highly accurate and widely used medical imaging technique primarily used to measure bone mineral density (BMD). This helps assess the risk of osteoporosis and fractures. However, DXA can also provide information about body composition, including fat mass and lean mass.

How Does DXA Work?

DXA uses two different X-ray beams with varying energy levels. These beams penetrate the body at different rates depending on the density of the tissue they encounter. The machine measures how much radiation passes through the body. This information is then used to calculate the density of various tissues, most importantly bone.

The X-Ray Process: Safe and Low Dose

The X-ray dose used in DXA is very low—significantly lower than a standard chest X-ray. The procedure itself is quick and painless. You'll lie on a table while the scanner passes over your body.

What DXA Can Measure

DXA provides valuable information on several key aspects of your health:

Bone Mineral Density (BMD): This is the primary use of DXA. It measures the amount of calcium and other minerals in a specific area of your bone. Low BMD is a key indicator of osteoporosis.
Bone Density T-Scores and Z-Scores: The scan results include T-scores and Z-scores, which compare your bone density to that of a healthy young adult (T-score) and to others of your age and sex (Z-score). These scores help determine your risk of fractures.
Body Composition: Beyond bone density, DXA can also measure your body fat percentage, lean body mass (muscle, organs, and bone), and fat distribution. This information is useful for assessing overall health and fitness.

Who Should Get a DXA Scan?

Your doctor may recommend a DXA scan if you:

Are a postmenopausal woman
Have a family history of osteoporosis
Are taking medications that can affect bone density
Have experienced a fragility fracture (a fracture that occurs from a minor fall or even without a fall)
Have other medical conditions associated with bone loss
Are a man over age 70

Preparing for a DXA Scan

The procedure is generally straightforward, but there are a few things to keep in mind:

Clothing: Wear loose-fitting clothing without metal fasteners.
Metal Objects: Remove any metal objects, such as jewelry or hair clips, before the scan.
Medication: Discuss any medications you are taking with your doctor.

Interpreting DXA Results

DXA results are typically reported as T-scores and Z-scores:

T-score: Compares your bone density to the average bone density of a healthy young adult. A T-score of -1.0 or higher is considered normal. A T-score between -1.0 and -2.5 indicates low bone mass (osteopenia), and a T-score of -2.5 or lower indicates osteoporosis.
Z-score: Compares your bone density to the average bone density of people your age and sex. A Z-score helps to identify bone loss that is unexpected for your age.

Your doctor will explain your results and discuss any necessary treatment or lifestyle changes. This might include dietary changes, exercise recommendations, or medication.

DXA vs. Other Bone Density Tests

While other tests can assess bone health, DXA remains the gold standard due to its precision and ability to measure BMD at specific sites. Other methods like quantitative computed tomography (QCT) or peripheral QCT (pQCT) may be used in certain situations, but they're not as widely used as DXA.

Conclusion

Dual-energy X-ray absorptiometry (DXA) is a safe, quick, and effective method for measuring bone density and assessing body composition. It plays a vital role in diagnosing and managing osteoporosis and related conditions. If you have concerns about your bone health, talk to your doctor about whether a DXA scan is right for you. Early detection and intervention can significantly reduce the risk of fractures and improve your overall well-being.