Bone Density Scan

What is a bone density scan?

A bone density scan, also known as a DEXA scan, is a type of low-dose x-ray test that measures calcium and other minerals in your bones. The measurement helps show the strength and thickness (known as bone density or mass) of your bones.

Most people's bones become thinner as they get older. When bones become thinner than normal, it's known as osteopenia. Osteopenia puts you at risk for a more serious condition called osteoporosis. Osteoporosis is a progressive disease that causes bones to become very thin and brittle. Osteoporosis usually affects older people and is most common in women over the age of 65. People with osteoporosis are at higher risk for fractures (broken bones), especially in their hips, spine, and wrists.

Other names: bone mineral density test, BMD test, DEXA scan, DXA; Dual-energy x-ray absorptiometry

What is it used for?

A bone density scan is used to:

• Diagnose osteopenia (low bone mass)
• Diagnose osteoporosis
• Predict risk of future fractures
• See if treatment for osteoporosis is working

Why do I need a bone density scan?

Most women age 65 or older should have a bone density scan. Women in this age group are at high risk for losing bone density, which can lead to fractures. You may also be at risk for low bone density if you:

• Have a very low body weight
• Have had one or more fractures after the age of 50
• Have lost a half inch or more in height within one year
• Are a man over the age of 70
• Have a family history of osteoporosis

Other risk factors include:

• Lack of physical activity
• Smoking cigarettes
• Heavy drinking
• Not getting enough calcium and vitamin D in your diet

What happens during a bone density scan?

There are different ways to measure bone density. The most common and accurate way uses a procedure called dual-energy x-ray absorptiometry, also known as a DEXA scan. The scan is usually done in a radiologist's office.

During a DEXA scan:

• You will lie on your back on a padded table. You will probably be able to leave your clothes on.
• You may need to lie with your legs straight, or you may be asked to rest your legs on a padded platform.
• A scanning machine will pass over your lower spine and hip. At the same time, another scanning machine called a photon generator will pass beneath you. The images from the two machines will be combined and sent to a computer. A health care provider will view the images on the computer screen.
• While the machines are scanning, you will need to stay very still. You may be asked to hold your breath.

To measure bone density in the forearm, finger, hand, or foot, a provider may use a portable scanner known as a peripheral DEXA (p-DEXA) scan.

Will I need to do anything to prepare for the test?

You may be told to stop taking calcium supplements 24 to 48 hours before your test. Also, you should avoid wearing metal jewelry or clothes with metal parts, such as buttons or buckles.

Are there any risks to the test?

A bone density scan uses very low doses of radiation. It is safe for most people. But it is not recommended for pregnant woman. Even low doses of radiation could harm an unborn baby. Be sure to tell your provider if you are pregnant or think you may be pregnant.

What do the results mean?

Bone density results are often given in the form of a T score. A T score is a measurement that compares your bone density measurement with the bone density of a healthy 30-year-old. A low T score means you probably have some bone loss.

Your results may show one of the following:

• A T score of -1.0 or higher. This is considered normal bone density.
• A T score between -1.0 and -2.5. This means you have low bone density (osteopenia) and may be at risk for developing osteoporosis.
• A T score of -2.5 or less. This means you probably have osteoporosis.

If your results show you have low bone density, your health care provider will recommend steps to prevent further bone loss. These may include:

• Getting more exercise, with activities such walking, dancing, and using weight machines.
• Adding calcium and vitamin D to your diet
• Taking prescription medicines to increase bone density

If you have questions about your results and/or treatments for bone loss, talk to your health care provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a bone density scan?

A DEXA scan is the most common way to measure bone density. But your health care provider may order more tests to confirm a diagnosis or to find out if bone loss treatment is working. These include a calcium blood test, a vitamin D test, and/or tests for certain hormones.