Bone Density
What is a Bone Density Scan?
A bone density scan, also called dual-energy X-ray absorptiometry (DXA/DEXA) or bone densitometry, is an enhanced form of X-ray technology used to measure bone loss.
A bone density scan is performed on the lower spine, wrists and hips for most patients. Bone density scans are today's established standard for measuring bone mineral density (BMD).
How does a bone density scan work?
Dual-energy X-ray absorptiometry machines utilize specialized software to compute and display bone density measurements on a computer monitor. During the bone scan, the DEXA machine emits a thin, invisible beam of low-dose X-rays with two distinct energy peaks. These pass through the soft tissue and the bones being examined. One peak is absorbed mainly by soft tissue and the other by bone. The soft tissue absorption rate can be subtracted from the total. The calculated difference is a patient's bone mineral density.
Why would you need a bone density scan?
A DEXA scan is most often used to diagnose osteoporosis, a condition that often affects women after menopause but may also be found in men. Osteoporosis involves a gradual loss of calcium, causing the bones to become thinner, more fragile and more likely to break. The DEXA scan can also assess an individual's risk for developing fractures. It is also effective in tracking the effects of treatment for osteoporosis and other conditions that cause bone loss.
The American College Radiology recommends a DEXA scan if you:
- are a post-menopausal woman and not taking estrogen
- have a personal or maternal history of hip fracture or smoking
- are a post-menopausal woman who is tall (over 5 feet 7 inches) or thin (less than 125 pounds)
- are a man with clinical conditions associated with bone loss
- have a history of prostate cancer or being treated with hormone therapy
- use medications that are known to cause bone loss, including corticosteroids such as Prednisone, various anti-seizure medications such as Dilantin and certain barbiturates, or high-dose thyroid replacement drugs
- have type 1 (formerly called juvenile or insulin-dependent) diabetes, liver disease, kidney disease or a family history of osteoporosis
- have high bone turnover, which shows up in the form of excessive collagen in urine samples
- have a thyroid condition, such as hyperthyroidism
- have a parathyroid condition, such as hyperparathyroidism
- have experienced a fracture after only mild trauma
- have had X-ray evidence of vertebral fracture or other signs of osteoporosis.
The Lateral Vertebral Assessment (LVA), a low-dose X-ray examination of the spine to screen for vertebral fractures that is performed on the DXA machine, may be recommended for older patients, especially if:
- they have lost more than an inch of height
- have unexplained back pain
- if a DEXA scan gives borderline readings.
Pre-exam instructions for a DEXA Scan
On the day of the DEXA scan you may eat normally. However, if you take calcium supplements, please do not take them for at least 24 hours before your bone scan.
You should wear loose, comfortable clothing, avoiding garments that have zippers, belts, clothing with rhinestones, rivets or buttons made of metal. You may be asked to remove some or all of your clothes and to wear a gown during the exam. You may also be asked to remove jewelry, eye glasses and any metal objects or clothing that might interfere with the X-ray images. A locker is available for you to store your personal belongings.
You may have to wait 10 to 14 days before undergoing a DEXA scan if you recently had a barium examination or have been injected with a contrast material for a computed tomography (CT) exam or scan that uses a radioisotope such as PET/CT.
To schedule your DEXA scan, please call us at (707) 525-4040. If you need to cancel, please call us 24 hours prior to your scheduled exam time.
The day of your DEXA scan
On the day of your DEXA scan, please arrive 15 minutes prior to your appointment time to check in and complete the necessary forms. Be sure to have your insurance information ready and available. Once you have registered, our technologist will escort you to an exam room.
If you are to have a Central DEXA examination, which measures bone density in the hip and spine, you will lie on a padded table. An X-ray generator is located below the table and an imaging device, or detector, is positioned above.
To assess the spine, your legs are supported on a padded box to flatten the pelvis and lower spine. To assess the hip, your feet are placed in a brace that rotates the hip inward. In both cases, you will need to hold very still as the machine slowly passes over the area, generating images on a computer monitor.
If you are to have a peripheral DXA Scan (PDXA) your finger, hand, forearm or foot is placed a small device that obtains a bone density reading within a few minutes.
The DEXA bone density test is usually completed within 10 to 30 minutes, depending on the equipment used and the parts of the body being examined.
After your DEXA scan
After your DEXA scan you are welcome to resume normal activities. Your scan will be evaluated by our Radiologists with a report sent promptly to your referring physician, who will be able to review the results with you.
Your test results will be in the form of two scores:
T score - This number shows the amount of bone you have compared with a young adult of the same gender with peak bone mass. A score above -1 is considered normal. A score between -1 and -2.5 is classified as osteopenia, the first stage of bone loss. A score below -2.5 is defined as osteoporosis. The T score is used to estimate your risk of developing a fracture.
Z score - This number reflects the amount of bone you have compared with other people in your age group and of the same size and gender. If this score is unusually high or low, it may indicate a need for further medical tests.
Small changes may normally be observed between DEXA scans due to differences in positioning and usually are not significant.
DEXA Scan side effects
There are no known side effects from DEXA scan.