People at risk for osteoporosis may benefit from a bone density scan every 2 years. A DEXA scan is the most common, but QCT scans are also an option. Medicare may cover the cost.

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Bone density scans are an important tool in predicting, diagnosing, and managing osteoporosis. Most people get a dual-energy X-ray absorptiometry (DEXA) scan. But there is also the quantitative computed tomography (QCT) scan.

Read on to learn more about how a bone density scan can help diagnose osteoporosis and other risk factors for bone fracture.

As you age, your bones become thinner, and your risk for conditions like osteopenia and osteoporosis increases.

A bone density scan measures the minerals in your bones. This helps show how strong your bones are. A decrease in bone mass is part of the diagnostic criteria for osteoporosis.

Before a DEXA or QCT scan, your doctor may recommend a peripheral bone density test. This test scans your wrist, heel, lower arm, or finger with a small machine.

DEXA and QCT scans usually measure your hips and spine.

DEXA scan

A DEXA scan uses low level X-rays to scan parts of your body vulnerable to fracture. During the test, one machine moves above you to scan the hip and lower spine area. Another machine scans the same areas below you, and the images are put together.

QCT scan

QCT machines also scan the body using X-ray technology. The scans combine to create a 3D image.

A QCT scan may provide a better estimate of trabecular bone (a type of highly porous bone), but it costs more and exposes you to more radiation than DEXA. A doctor won’t usually use a QCT unless DEXA is not available.

Researchers primarily use QCT to improve our understanding of osteoporosis. A healthcare team may also use it to monitor how well any drugs you take are working.

Anyone at risk of losing bone density should consider a bone density scan. You are at higher risk if you:

  • were assigned female at birth and are over the age of 65
  • were assigned male at birth and are over the age of 70
  • had at least one bone fracture before the age of 50
  • have very low body weight
  • have become shorter by at least 1 inch in the past year
  • have a family history of osteoporosis
  • have had exposure to chemotherapy or radiation

You usually do not need a bone density scan more frequently than every 2 years. Your doctor may recommend a different timeline depending on your personal risk factors.

You can come to the exam dressed in comfortable clothing. Medical staff may ask you to remove any jewelry and clothing with zippers or other metal.

Before the scan, a healthcare professional may ask health questions, such as if you may be pregnant. They may also recommend stopping calcium supplements a day or two before the procedure.

During a DEXA or QCT scan, you will lie on your back on a table.

During a DEXA scan, you might prop your legs up on a padded box, so your knees are bent. The machines move above and below you as you stay in the same spot.

During a QCT scan, the table moves into the CT machine. The machine rotates around you, taking X-ray images.

It’s best to lie very still during a DEXA or QCT scan. This is to prevent images from being blurry. The technicians may ask you to hold your breath.

Bone density scans take about 10 to 20 minutes.

A DEXA scan uses low levels of radiation. These are similar to the levels of radiation used in X-rays. DEXA scans are generally safe but may slightly increase your risk of future cancer.

A QCT scan uses a much higher dose of radiation, but doctors still consider it safe.

DEXA and CT scans express bone mineral density test results differently.

DEXA scan results

DEXA scans provide a T-score. Your T-score is a comparison of your bone mineral density to a healthy young adult, also called the mean. If it’s the same, your T-score is 0. The T-score measures your bone density in standard deviations (SD) from the mean.

within 1 SD of the meanhealthy bone mass
between 1 and 2.5 SD below meanlow bone mass
2.5 SD or more below meanosteoporosis

Severe osteoporosis is when the score is more than 2.5 SD below the mean, and you have had at least one fracture.

You may also get a Z-score which is your score compared to someone else of the same age.

QCT scan results

A doctor can convert your hip QCT scan results into an image that can give a T-score similar to a DEXA scan.

There is no standard measurement of spine QCT scores for the diagnosis of osteoporosis. But it’s possible to translate the results of a spine QCT to approximate T-score categories.

What else can a bone density scan detect?

Bone density scans can detect osteopenia, which is the loss of bone mineral density that does not meet the criteria for osteoporosis.

QCT scans can measure bone mineral density and muscle mass. CT scans can give detailed images of bone fractures, joint erosion, or cancerous tumors.

Bone density scans show the amount of bone but may not show bone quality. They cannot predict fractures as there are other risk factors for bone fracture besides mineral density.

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Out-of-pocket costs for a DEXA scan range from $160 to $1319, depending on where you live and which services the clinic provides. Medicare covers the cost of a scan once every 24 months if you meet the program’s criteria.

DEXA and QCT are two safe scans to determine bone mineral density. They are useful in diagnosing osteoporosis and osteopenia but do not provide a full picture of fracture risk. Medicare may cover the cost of the procedure if you qualify.