What Is a DEXA Scan?

A DEXA scan is a non-invasive test that measures bone mineral density to assess if a person is at risk for osteoporosis or a fracture.

DEXA stands for dual-energy X-ray absorptiometry, meaning two X-ray beams are aimed at the bones during the scan. It is also called a central DEXA scan, bone densitometry scan, or DXA scan.

A DEXA scan can detect changes in bone density as small as 1%, making it more sensitive and accurate than a regular X-ray, which shows changes in bone density after bone loss of about 40%.

This article explains a DEXA scan, who might need one, the procedure, and the results.

What Is a DEXA Bone Scan?

A DEXA scan can diagnose if someone has osteoporosis or bone thinning. It uses X-rays and determines a bone mineral density (BMD) score. BMD allows you and your healthcare provider to understand how strong your bones are.

BMD from a DEXA scan can help identify osteopenia, osteoporosis, and fracture risk.

• Osteopenia means an individual has low bone mass and is at risk for developing osteoporosis.
• Osteoporosis means an individual has low bone density and is at risk for a fracture.
• The fracture risk assessment tool helps to assess the likelihood of experiencing a fracture over a 10-year period. The results from the DEXA scan make this prediction more accurate.

Nearly one-fifth of females over the age of 50 will develop osteoporosis in their lifetime. Osteoporosis can affect men, too, although it is less frequent.

Understanding BMD is essential because you and your provider can utilize medications and lifestyle modifications to slow or prevent further bone thinning. DEXA scans can help track BMD to determine if your medications and lifestyle modifications are working to prevent further bone loss.

Other Bone Imaging Tests

While a DEXA scan is considered the gold standard for osteoporosis screening, other options are available. These other tests that look at BMD include:

• MRI
• Opportunistic CT (oCT)
• Quantitative CT (qCT)

A DEXA scan is solely used to assess BMD. If there are concerns about cancer or other conditions affecting the bones, an MRI may be utilized since it allows for detailed imaging of the bone. An MRI can identify causes of bone pain (e.g., in cases of back pain) or cancer.

An oCT scan means that the patient is undergoing a CT scan for a reason other than bone mineral density but is at risk for osteoporosis. So, a CT scan is done for the original health concern, and then the provider also takes the opportunity to look for any vertebral fractures and measure bone density.

A qCT scan is a CT scan specifically used to measure BMD. If a DEXA scanner is not available and the BMD must be known, a provider may use a qCT.

A DEXA scan uses X-rays, which are less radiation than a CT scan. This is one reason why a DEXA scan is generally preferred over a CT scan for BMD. However, if an individual is already undergoing a CT scan, it may be a good option to screen for BMD to determine if further workup is necessary.

Who Should Have a DEXA Scan?

Females are at a higher risk of osteoporosis than men. It is recommended that females who are age 65 and older and who have gone through menopause receive a DEXA scan.

If you have one of the following conditions, your healthcare provider may recommend a DEXA scan sooner than age 65. These conditions all increase the risk of a fracture in both males and females:

• Cigarette smoking
• Long-term steroid use
• Low body weight
• Rheumatoid arthritis
• Family history of non-traumatic bone fractures
• Alcohol consumption of three or more drinks per day
• Other health conditions that can affect bone density, such as diabetes, early menopause, chronic liver disease, thyroid conditions, and conditions that affect nutrient absorption

DEXA scans are not as routinely recommended for males as they are for females. This is because men are at a lower risk of osteoporosis than females. Additionally, while screening tools, such as DEXA, accurately predict BMD in both males and females, medications to treat osteopenia or osteoporosis may not be as effective in males as females.

Medication effectiveness may differ between males and females due to differences in hormones, such as estrogen and testosterone. While Medicare does cover DEXA scans for males with certain risk factors, it is essential to work closely with your healthcare provider for the most up-to-date screening and treatment options.

Limitations and Contraindications DEXA Scans

Certain conditions can make DEXA scans less accurate. Additionally, there are considerations for individuals who are pregnant since the test utilizes radiation, which can be harmful during pregnancy.

Instances where DEXA scans may not be as accurate include:

• Recent use of oral contrast of radionucleotides (a special drink that is used to help diagnose or treat various conditions, such as cancer)
• Severe degenerative changes or a severe fracture that caused deformity in the area being measured
• Foreign material in the area being measured, such as implants or hardware from a previous fracture
• Patient mobility issues that prevent them from lying in the correct position or staying still
• Extremely high or low body mass index (BMI)

Different machines have various weight limitations. In instances where an individual has a high BMI, other screening tools, such as a quantitative CT, might be a better option.

If you are pregnant, discuss the risks and benefits of the exam with your healthcare provider. They may recommend delaying the scan until after pregnancy or until you are farther along.

How a DEXA Scan Is Performed

A DEXA scan is a quick outpatient procedure that typically lasts approximately 10 minutes, although it may last slightly shorter or longer.

Since the test utilizes X-rays, any metal can interfere with the results. Many facilities may ask you to wear a gown or provide instructions for what clothing you can wear (e.g., no zippers or metal buttons). You will also be asked to remove any jewelry.

The technician running the test will likely ask if you are pregnant or if there is a chance you are pregnant. If they don't, be sure to tell the medical staff if you are pregnant or think you might be.

To complete the DEXA scan:

• You will lie on an examination table while the X-ray machine scans the area of bone being examined. The technician may ask you to change positions or lie in certain ways to obtain more accurate scans.
• The technician may ask you to lie still and hold your breath for a few seconds at a time during the scan.
• The technician will help position your body for the scan. They may place your legs on a padded box or put your foot in a device to help it turn inwards to scan your hips better.
• They will then help you up and off the table and you will be able to change back into your clothes if you were wearing a gown.

If you are already taking calcium supplements, your healthcare provider may ask you to stop taking them 24 hours prior to your test. Contact your healthcare provider for advice before the scan so you know if you need to stop taking any medications or supplements.

Understanding Results from a DEXA Scan

After the scan, your healthcare provider will follow up with the results. Follow-up time varies, but generally, you can expect to hear from your provider within a few days.

When you get results from a DEXA scan, you'll be given two scores: T score and Z score.

T score: The T score compares your bones with bones that are considered healthy. So, a T score is comparing your bone density with that of young, healthy adult bones.

Z score: The Z score compares your bones with those of others who are of similar age.

The T-score is what is commonly looked at because it shows age-degenerative changes.

T scores fall into the following categories:

• T score between -1 to +1 is considered normal.
• T score between -1.1 to -2.4 is considered osteopenia (at risk for osteoporosis).
• T score of -2.5 or less indicates osteoporosis. (Since these are negative numbers, a T score of -3 would be less than a T score of -2.5.)
  

Several treatment options exist. The most widely used medications are bisphosphonates. If your scores indicate you have osteopenia or osteoporosis, your healthcare provider will likely work with you to develop a treatment plan and then perform a repeat DEXA scan to monitor treatment.

Cost of a DEXA Scan

A DEXA scan is covered by insurance plans similar to other screening tools such as mammograms or colonoscopies. However, certain conditions must be met in order for insurance to cover the test. For example, Medicare will cover bone mass tests once every 24 months, or more frequently if medically necessary, if one of the following conditions is met:

• Females who are estrogen-deficient and at risk for osteoporosis
• X-rays show possible osteoporosis, osteopenia, or vertebral fractures
• Individuals taking prednisone (a steroid) or are planning to
• A diagnosis of primary hyperparathyroidism
• Monitoring to determine the effectiveness of osteoporosis medication
  

Different insurance plans vary in their coverage. Contact your carrier prior to your scan to understand if you are responsible for any out-of-pocket costs.

Summary

DEXA scans are a safe screening tool to measure BMD and help diagnose conditions such as osteopenia and osteoporosis. They can also be used to monitor the effectiveness of treatment for these conditions.

Since DEXA scans are considered a screening tool and help prevent costly conditions, such as fractures, most insurance providers cover them at minimal or no cost to the patient, provided the patient meets the criteria for needing one.