Bone density scan

A bone density scan, also called a DXA scan or dual-energy X-ray absorptiometry, uses X-rays to evaluate your bone health. Unlike a regular X-ray that produces a picture of your bones, a bone density scan measures the strength and quality of your bones. This scan helps health care providers diagnose and monitor osteoporosis (weakened bones) and assess your risk for fractures. A bone density scan is a quick, painless, and noninvasive exam.

A bone density scan uses ionizing radiation, the same type of energy X-rays use. A machine sends two different energies of X-ray beams through your body, both containing a low dose of radiation. Dense bone with a high amount of calcium absorbs radiation, so it doesn’t pass through your body to the radiation detector. Bones with low mineral density allow more radiation to pass through. Dense bones appear white on the scan; weak bones appear gray.

The detector in the DXA machine measures the radiation that passes through your body. Your health care provider compares this measurement to the optimal bone density of a young adult, which gives them your T score. T scores are measured in negatives. The closer to zero your T score, the healthier your bones.

Most bone density tests use a central device, meaning they measure mineral density in your hips and lower spine. Peripheral devices measure density in your forearm, wrist, fingers, leg, or heel. Central devices tend to be more accurate and are available at hospitals and imaging facilities. Peripheral devices are smaller and portable, so you might see them at a doctor’s office or health fair.

In some cases, quantitative computed tomography (QCT) is used to measure bone density. This test uses CT scans instead of X-rays to create more detailed 3D images of the bones. We may recommend QCT for people who have:

• A condition that requires steroid therapy
• A very tall or short stature (height)
• Degenerative spine disease
• Obesity
• Parathyroid disease

Trabecular bone score (TBS)

TBS is an advanced tool, added to a standard DXA scan, that can provide more information about the quality and texture of bones in your hips, spine, and wrists. This FDA-approved software can help predict fracture risk with more accuracy, so we can make an effective prevention plan. Penn Medicine offers TBS at select locations. Ask your referring provider if it’s right for you.

Bone density scan vs. bone scan

A bone scan is different than a bone density scan. A bone scan is a type of nuclear medicine scan, which is an imaging exam that uses a radioactive substance to detect areas of high biochemical activity in your body. We may recommend a bone scan to diagnose bone infections, tumors, or cancer.

The most common reasons for a bone density scan are to diagnose osteoporosis or osteopenia (low bone density, which may develop before osteoporosis). We use bone density tests to monitor these conditions after you start treatment. A bone density scan can help us evaluate your risk of bone fractures. Your health care provider takes other factors into consideration when assessing your fracture risk, including your age, weight, lifestyle, and family history.

You may need a bone density scan if you:

• Are a man older than 75 (or 50 to 69 with risk factors)
• Are a woman older than 65 (or 50 to 64 with risk factors)
• Have a family history of osteoporosis or fractures
• Have a history of fractures after the age of 50
• Have a low body weight

Other reasons your health care provider may recommend bone density testing include:

• History of smoking
• Kidney disease
• Liver disease
• Taking medications that are known to cause bone loss, such as corticosteroids or immunosuppressants
• Thyroid or parathyroid disease
• Type 1 diabetes

A radiation technologist, or radiographer, performs your scan. A radiologist, rheumatologist, or endocrinologist reviews and interprets your scan.

There’s not a lot of special preparation for a bone density scan, but you should tell your provider if you:

• Take vitamins or supplements: You may need to stop taking some supplements, such as calcium, 24 hours before the scan.
• Have had another imaging exam within 24 hours: The contrast materials from a CT scan or barium swallow may affect the results of a bone density scan.
• Are pregnant: Ionizing radiation can harm a fetus (unborn baby), so your provider may delay your scan or choose another type of imaging.

A bone density scan takes 10 to 30 minutes. Here’s what you can expect during a scan with a central device:

1. You should wear comfortable clothing and remove any jewelry or metal items. We may ask you to change into a gown for the exam.
2. You lay down on a padded table that has a scanning arm and detector over it. The machine is open, so you won’t be enclosed.
3. The technologist may place foam blocks under your knees to flatten your lower back.
4. The machine sends X-rays from beneath you, through your body, and up to the detector above you.
5. The scanning arm moves back and forth over your body as the detector captures the radiation and produces images on a computer.

A bone density scan is an outpatient procedure that doesn’t require sedation or anesthesia, so you can drive and return to normal activities right away. The radiologist who reviews your scan shares the results with your referring provider. Depending on your T score, your provider may recommend lifestyle changes or medication to improve your bone health.

A bone density scan uses a very low dose of ionizing radiation. There is little risk of the radiation harming tissue or causing cancer. Experts agree that the benefits of the scan in detecting bone loss and predicting fracture risk outweigh the small risk of radiation exposure.

At Penn Medicine, we prioritize comfort, safety, and quality when it comes to your imaging scan. You’ll find advanced technology, experienced radiographers, and board-certified radiologists. We offer:

• Expertise in bone disorders: We specialize in common and complex bone disorders, including osteoporosis, osteopenia, Paget’s disease, and parathyroid disorders. The Penn Bone Center offers comprehensive screening, diagnosis, and treatment from a team of experts.
• Multispecialty approach: Endocrinologists, radiologists, pharmacists, and other specialists collaborate to ensure you receive the right imaging exams and tests for your age, gender, and lifestyle. We help you reduce the risk of fractures and achieve better bone health.
• Convenient access: It’s easy to get the tests you need at a time and place that works for you. DXA scans are available at most Penn Medicine Radiology sites. We regularly upgrade our equipment and do quality assessments according to guidelines from the International Society of Clinical Densitometry.