Patient education: Dual-energy X-ray absorptiometry (The Basics)

What is dual-energy X-ray absorptiometry? — Dual-energy X-ray absorptiometry, or "DXA," is a test that measures something called "bone density." It is used to check how strong your bones are.

As people age, their bones often become less dense. This means that the bones are thinner and more fragile. Over time, this can lead to a disorder called "osteoporosis," which makes bones weak and more likely to fracture (break). DXA might be done to see if you have osteoporosis or are at risk for it. Or if you already know you have osteoporosis, DXA can show if treatments are working.

How do I prepare for DXA? — Your doctor or nurse will tell you if you need to do anything special to prepare.

●Schedule your DXA appointment 1 to 2 weeks after getting certain tests that use a special dye called "contrast." These include MRI or CT scans. If you take calcium supplements, your doctor might tell you to stop taking them for 24 hours before the test. Having contrast or calcium in your body can make the DXA results inaccurate.

●Do not have DXA if you are pregnant or might be pregnant.

●Wear comfortable clothing without any zippers, buckles, or other metal pieces to your appointment. This way, you can keep your clothes on during the test.

What happens during DXA? — During DXA, you lie on a table. You might need to remove your clothes and put on a gown. Then, an X-ray machine scans your bones. The test usually looks at your lower spine and hip bones. In some cases, it will look at other bones, like the forearm.

DXA is not painful or uncomfortable. It takes about 5 to 10 minutes.

What happens after DXA? — After the test, a doctor will look at the pictures of your bones. They will also review the "T-score" and the "Z-score." These mean slightly different things:

●T-score – This number shows the amount of bone you have compared with an average young person with healthy bones. A T-score of less than -2.5 means that you have osteoporosis. In general, the lower the T-score, the greater your risk of fracture (breaking a bone).

●Z-score – This number shows the amount of bone you have compared with an average person the same age as you.

Based on these numbers, your doctor can tell you if you have osteoporosis or are at risk.

Your doctor or nurse will discuss your results with you. They can help you understand what the results mean and what to do next. They will also talk to you about whether you should start or continue medicines to treat osteoporosis. This decision is based on your T-score and your risk of fracture over the next 10 years. They will also talk to you about when to get another DXA. This will help them see how your bones change over time.

What are the downsides of DXA? — DXA does not usually have any risks to your health.

Even though DXA is a type of X-ray, it gives off very little radiation. During DXA, you get about the same amount of radiation that an average person gets from the environment in 1 day.

More on this topic

Patient education: X-ray (The Basics)
Patient education: Bone density testing (The Basics)
Patient education: Osteoporosis (The Basics)
Patient education: Paget disease of bone (The Basics)

Patient education: Bone density testing (Beyond the Basics)
Patient education: Osteoporosis prevention and treatment (Beyond the Basics)
Patient education: Paget disease of bone (osteitis deformans) (Beyond the Basics)