Bone Density

Test Overview

A bone density test is a kind of X-ray test. It measures the density of minerals (such as calcium) in your bones. This information helps your doctor estimate the strength of your bones.

We all lose some bone mass as we age. Bones naturally become thinner (called osteopenia) as you grow older. This is because existing bone tissue is broken down faster than new bone is made. As this occurs, our bones lose calcium and other minerals. They also become lighter and less dense. This makes the bones weaker and makes them more likely to break (fracture).

With further bone loss, osteopenia can lead to osteoporosis. So the thicker your bones are, the longer it takes to get osteoporosis. Although osteoporosis can occur in men, it is most common in women older than age 65.

If your bone density is lower than normal, you can increase it and your strength. You can do things like exercising, lifting weights or using weight machines. You can also make sure to get enough calcium and vitamin D. And you may need to take certain medicines.

There are several different ways to measure bone density.

• Dual-energy X-ray absorptiometry (DXA). This is the most accurate way to measure bone density. It uses two different X-ray beams to estimate bone density in your spine and hip. Strong, dense bones allow less of the X-ray beam to pass through them. The amounts of each X-ray beam that are blocked by bone and soft tissue are compared to each other. DXA can measure as little as 2% of bone loss per year. It is fast and uses very low doses of radiation. Single-energy X-ray absorptiometry (SXA) may be used to measure bone density in the heel and forearm. But SXA is not used as often as DXA.
• Peripheral dual-energy X-ray absorptiometry (P-DXA). P-DXA is a type of DXA test. It measures the density of bones in the arms or legs, such as the wrist. It can't measure the density of the bones most likely to break, such as the hip and spine. P-DXA machines are portable units that can be used in a doctor's office. P-DXA also uses very low doses of radiation. The results are ready faster than standard DXA measurements. P-DXA is not as useful as DXA for finding out how well medicine used to treat osteoporosis is working.
• Dual photon absorptiometry (DPA). This test uses a radioactive substance to measure bone density. It can measure bone density in your hip and spine. DPA also uses very low doses of radiation. But the scan takes longer than the other methods.

Ultrasound is a screening test that is sometimes offered at events such as health fairs. If results from an ultrasound test find low bone density, DXA is advised to confirm the results. Ultrasound uses sound waves to measure bone density, usually in your heel. It is quick and painless. And it does not use potentially harmful radiation like X-rays. One downside of ultrasound is that it can't measure the density of the bones in the hip and spine. These are the bones most likely to fracture from osteoporosis. Ultrasound is not used to keep track of how well medicine for osteoporosis is working.

Before you are screened for osteoporosis, you may want to think about what you will do if the tests show that you have a high chance of getting osteoporosis.

Osteoporosis: Should I Have a Dual-Energy X-Ray Absorptiometry (DXA) Test?