Bone Density Scan (DXA or DEXA)

Dual-energy X-ray absorptiometry (DXA or DEXA) is a scan that is used to determine the density of bone to assess its strength. It is a standard method for diagnosing osteoporosis; used in combination with risk factors (the so-called “FRAX” method), it is also considered an accurate way to estimate fracture risk.

DXA works by sending two low-dose X-rays which are absorbed differently by bones and soft tissues. The density profiles from these X-rays are used to calculate bone mineral density. The lower the density, the greater the risk of fracture. DXA is painless and takes about 10 minutes. The amount of radiation is very low, about 10 percent of a normal chest X-ray.

DXA can determine bone mineral density for any bone but is most commonly used for hip and lumbar (lower) spine. The examination can also be used to perform vertebral fracture assessment. This screening is used to uncover bone problems of the skeleton, for example in people who have unexplained back pain or who have experienced a loss in height of more than an inch in a year. Vertebral fractures are often asymptomatic.

A bone mineral density assessment may be considered every two years, depending on age, gender, and other factors. See below for specific recommendations.

Osteoporosis Screening

According to the International Osteoporosis Foundation, osteoporosis is estimated to affect 200 million women worldwide. Men also experience the condition, which weakens bones and makes them subject to fracture. Though more women than men have osteoporosis, men are more likely than women to die after breaking a hip.

Regular screening can diagnose osteoporosis and other bone problems early. That way they can be managed and even curbed with prescription medicines and lifestyle modifications.

How important is bone health?

Assessing your bone health may not seem like a critical health priority but consider these facts:

  • In women over 45, osteoporosis accounts for more days hospitalized than diabetes, myocardial infarction, and breast cancer.
  • The overall mortality is about 20 percent in the first 12 months after hip fracture.
  • About 20-25 percent of hip fractures occur in men. Men who break a hip are more likely to die than women who do the same.

Clinical Indications

There are a number of conditions related to poor bone health. People who should consider assessment with DXA include:

  • Women 65 and older and men over age 70
  • Women under age 65 and men ages 50 - 70 who have risk factors such as:
    • A fracture over age 50
    • Rheumatoid arthritis or chronic kidney disease
    • Eating disorders
    • Early menopause (from natural causes or surgery)
    • History of hormone treatment for prostate or breast cancer
    • Significant loss in height 
    • Smoking
    • Family history of osteoporosis
    • Taking corticosteroids (prednisone, methylprednisolone) every day for 3 months or more
    • Three or more alcoholic drinks per day on most days.

Benefits of DXA at UCSF

UCSF researchers and physicians are among the world’s leaders in bone health.

  • UCSF pioneered the use of DXA to assess bone health
  • Offering swift and painless procedure
  • Interdisciplinary team allows for the most comprehensive treatment plan to prevent further bone loss or injury.

Research and Collaboration Help

UCSF researchers work collaboratively with other departments to find out how to reduce the likelihood of osteoporosis. Learn more about the Bone Quality Research Lab (Principal Investigator Galateia J. Kazakia, PhD). The UCSF Skeletal Health Service is a collaboration of specialists in metabolic bone, endocrinology, rheumatology, and nephrology providing clinics at the Orthopaedic Institute. 

Bone Density Scan Location

UCSF Imaging Center at Montgomery Street
1725 Montgomery Street
San Francisco, CA 94111
Ph: (415) 502-1330 (press “option 1”)
Fax: (415) 986-2213
Hours: Monday-Friday, 8:00am-5:00pm

The DXA Procedure

DXA is a quick, painless test, as simple as an X-ray, just with slightly larger equipment. You'll lie on your back and have two scans, turning your body between scans to get the optimal angles.

How long does DXA take? The entire appointment time is about 30 minutes, with the scan itself taking less than 10. 

Making an appointment

  • DXA is not recommended if you’re pregnant. Tell your doctor if there’s any chance you might be pregnant. If it’s critically important that DXA being performed during pregnancy, the distal forearm can be examined.  
  • Tell your doctor if you recently had a barium exam or have been injected with a contrast material for a computed tomography (CT) scan or radioisotope scan. You may have to wait 10 to 14 days before undergoing DXA.

24 hours prior to your exam

Take no calcium supplements

On the day of your exam

  • Wear loose, comfortable clothing with no metal attachments such as zippers or metal buttons.
  • You may be asked to remove some of your clothing and wear a gown.
  • You’ll be asked to remove any jewelry, eyeglasses, removable metal dental appliances, and any other metal objects that might interfere with X-rays.

After the exam

Your results will be read by a UCSF doctor of radiology with experience in bone health. This doctor will interpret your results and send that report to the physician who referred you, who will review them with you.

Your test results will have two scores:

T score — This number shows how much bone you have compared with a young adult of your gender who has peak bone mass. A score above -1 is considered normal. A score between -1.1 and -2.4 is considered to be low bone mass or osteopenia. A score of -2.5 and below indicates osteoporosis.

Z score — This number compares your amount of bone with others of your age, gender, and size. If this score is unusually high or low, you might need further testing. 

If your results indicate osteopenia or osteoporosis, you and your doctor can decide on a treatment plan that could include medications and/or lifestyle modifications. 

Another bone density exam is called quantitative computed tomography (QCT).

Billing & Insurance

UCSF’s Radiology Billing Department is happy to answer any questions about billing or provide price estimates for any radiology services. Call 415-514-8888.

Our Radiologists

Professor, & Division Chief, Musculoskeletal Radiology
Clinical Director of MQIR
Director, T32 Program
Professor in Residence
Associate Professor
Associate Chair, Wellbeing and Professional Climate
Associate Professor In Res.
Associate Professor
Director of Musculoskeletal Ultrasound
Asst. Prof of Clin Radiology
Professor Emeritus
Prof of Clinical Radiology
Assistant Professor
Orthopaedic Surgery
Associate Clinical Professor