Purpose, Preparation, Risks, and Results

A dual-energy X-ray absorptiometry (DEXA) scan is an imaging test that measures the amount of calcium and other minerals in your bones. The measurement indicates bone density, which is bone strength and thickness.

A DEXA scan is most frequently used as a screening tool for osteoporosis, a condition that makes your bones brittle and weak. You might also hear a DEXA scan referred to as a DXA scan, bone mineral density scan, or bone densitometry.

A DEXA scan can diagnose osteopenia and osteoporosis and predict your risk of future fractures. If you’ve already been diagnosed with osteoporosis, the scan can check if your bone density shows changes in response to treatment.

You may have osteopenia if your bones are thinning more than is typical for your age. In addition to aging, family history, poor bone mass development in younger years, and certain medications and conditions can put you at risk for osteopenia. Osteopenia also puts you at risk for osteoporosis, which increases your risk of fracture.

Because the risk for fracture in osteoporosis is highest at the hips, spine, and wrist, a DEXA scan will usually measure these bones. It can also measure the fat and muscle composition in specific parts of the body, including the arms, legs, and pelvis.

Who Needs a DEXA Scan?

Because of the increased risk of osteoporosis and fracture, a DEXA scan is usually recommended for women older than 65 and men older than 70. Women who are younger than 65 but who are at higher risk for osteoporosis might also need a DEXA scan. You may be at risk for osteoporosis at a younger age if you have:

• Estrogen deficiency
• Low body mass (less than 127 pounds)
• A mother who fractured her hip at any age
• No period for over a year before you’re 42

Women younger than 65 and men younger than 70 may also need a DEXA scan if they smoke, have gotten shorter, or have experienced a severe curving of the upper spine (thoracic kyphosis).

DEXA screening is also recommended for anyone taking medicines that may affect their bone mineral density. These medications include anticonvulsants and chronic heparin, an anticoagulant.

Some conditions, including rheumatoid arthritis, hyperthyroidism, and Cushing’s disease, may also negatively affect bone mineral density. See if you should get screened for bone mineral density loss if you have a condition that can impact your bone strength.

Because a DEXA scan can also be used to measure body mass and body fat, a healthcare provider may order a DEXA scan if you have:

• Cancer
• Eating disorders
• Malabsorption—the body’s inability to properly absorb nutrients

The DEXA scan uses low-energy X-rays of different energy levels to measure bone density. Compared to the other scans available for the screening of your bone health, a DEXA scan is relatively inexpensive and has a shorter scan time.

Before the Test

Before the scan, a doctor may measure your weight and height. For the scan, you will be asked to either lie on the padded scanner table or sit upright next to the table. If you are lying down, your legs will either be straight out or resting on a padded box. Your foot might also go in a device to turn your hip inward.

During the Test

The table has an instrument above and below the table that makes a large C-shape. Two scanning machines work simultaneously to take images of whichever body part a healthcare provider requested tests. In addition, if you are getting a DEXA scan to measure your fat and muscle composition, the machine will scan your entire body.

The healthcare provider may ask you to hold your breath for a few seconds during the scan. It’s important to stay still while the scanner is taking the images. The test usually takes 15-20 minutes.

After the Test

The images are sent to the technician’s computer, which a healthcare provider later views. Your provider will follow up with your scan results and recommendations for any treatment or further testing that may be needed.

DEXA scans are generally considered safe. The radiation exposure is small and comparable to the background radiation of everyday life.

Although the radiation exposure is small, the test is not recommended for people who are pregnant. That’s because even low doses of radiation can be dangerous for an unborn baby. Talk with a healthcare provider if you are pregnant or think you might be pregnant.

The scan also slightly increases the possibility of cancer in the future. While everyone is exposed to some types of radiation in daily life, any additional exposure—such as through an imaging test—can marginally increase cancer risk. The increased risk is similar to that of a regular X-ray. Talk to a healthcare provider to weigh the risk of radiation exposure and the benefits of a DEXA scan.  

A healthcare provider may ask you to stop any calcium supplements 24-48 hours before the scan. You should also avoid wearing metal jewelry or clothing with metal on it.

People who are pregnant or think they might be pregnant should talk to their healthcare provider before going for a scan. If you have not yet gone through menopause, you’ll be asked if there is any possibility that you might be pregnant. You may also be asked to give a urine sample so the facility can make sure you aren’t pregnant before administering the X-ray.

A healthcare provider may ask you to bring the results of any previous scan. They’ll want to examine the changes in your bone mineral density between the tests.

The results of the DEXA scan usually fall into two scoring systems: the T-score and Z-score. These scores help healthcare providers learn more about bone mineral density and bone health.

In the T-score, your bone mineral density is compared to that of a healthy 30-year-old. In the Z-score, your results are compared to the bone mineral density of people of the same age, sex, and race.

Interpreting Your Results

With both T- and the Z-scores, the lower the number, the thinner your bones—and the higher your risk for fracture. The following T-scores can indicate normal or higher-than-normal bone loss:

• Normal bone density: -1.0 or above
• Osteopenia: Between -1 and -2.5
• Osteoporosis: Below -2.5