What Is a DEXA Scan?

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 the bone’s density, or the bone’s strength and thickness.

A DEXA scan is most frequently used as a screening tool for osteoporosis, a condition that makes your bone brittle and weak.

You might also hear a DEXA scan be referred to as a DXA scan, bone mineral density scan, or bone densitometry.

Purpose

As you get older, your bones usually get thinner. If the bones are thinning more than typical for your age, you may have osteopenia. Besides aging, family history, poor bone mass development in younger years, and certain medications and conditions can put you at risk for osteopenia.   

Osteopenia puts you at risk for osteoporosis. Osteoporosis increases your risk of fracture.

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

Because the risk for fracture in osteoporosis is highest at your hips, spine, and wrist, these are the bones that a DEXA scan will usually measure. 

A DEXA scan 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 increased risk of osteoporosis and fracture, a DEXA scan is usually recommended for women older than 65 years and men older than 70 years.

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
• A mother who fractured her hip at any age
• Low body mass (less than 127 pounds)
• 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 who is 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, your healthcare provider may order a DEXA scan if you have:

• Malabsorption
• Cancer
• Eating disorders

What Do DEXA Scan Results Mean?

The results of the DEXA scan usually come under two scoring systems known as the T-score and Z-score. These scores help your healthcare provider know your 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.

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

How to Prepare

Your 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.

If you’ve had any previous scan, your healthcare provider may ask you to bring the results so they can look at the changes in your bone mineral density between the tests.

What to Expect

The DEXA scan uses two X-rays of different energy levels to measure bone density. The X-rays are low energy.

Before the scan, a healthcare provider 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 so that your hip is turned inward.

The table has an instrument above and below the table that make a large C-shape. Two scanning machines work simultaneously to take images of whichever body part your healthcare provider requested tests.

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.

The images are sent to the technician’s computer, which your 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.

If you are getting a DEXA scan to measure your fat and muscle composition, the machine will scan your entire body.

Are DEXA Scans Safe?

DEXA scans are generally considered safe. The radiation exposure is small and is comparable to 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 your 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.  

As compared to the other scans available for the screening of your bone health, DEXA scan is relatively inexpensive and has a shorter scan time.

A Quick Review

A DEXA scan, or bone mineral density scan, is an imaging test used to check your bone health. The scan uses two low-energy X-rays to take images of bones of the hip, spine, and wrist. The X-rays measure the amount of calcium and other minerals in your bones, showing the bone’s density. A DEXA scan can help in the diagnosis of osteopenia and osteoporosis. The scan can also help predict fracture risk and manage already-diagnosed osteoporosis. DEXA scans can also measure your fat and muscle composition in certain areas of the body, making the scan a potential step in the diagnosis or treatment of conditions like malabsorption. Talk to your healthcare provider about why a DEXA scan is being ordered, what you should do to prepare, and what treatment options may be available depending on your results.