What is a Bone Density/DEXA Scan?
Bone density scanning, also called dual-energy x-ray absorptiometry (DXA, DEXA) or bone densitometry, is an enhanced form of x-ray technology that is used to measure bone mineral density (BMD).
DXA is most often performed on the lower spine and hips 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, as well as structural changes, causing the bones to become thinner, more fragile and more likely to break. It is also effective in tracking the effects of treatment for osteoporosis and other conditions that cause bone loss. The test can also assess an individual’s risk for developing fractures. The risk of fracture is determined by age, body weight, history of prior fracture, family history of osteoporotic fractures and life style issues such as cigarette smoking and excessive alcohol consumption.
The DXA equipment used at YVMC measures bone density in the hip and spine
How should I prepare?
On the day of the exam you may eat normally. You should not take calcium supplements for at least 24 hours before your exam.
You should wear loose, comfortable clothing, avoiding garments that have zippers, belts or buttons made of metal. You may be asked to remove some or all of your clothing and wear a gown during the exam. Any metal object might interfere with the x-ray images.
Inform your ordering physician and the technologist if you recently had a barium examination or have been injected with a contrast material for computed tomography (CT) scan or radioisotope (Nuclear Medicine) scan. You may have to wait 10 to 14 days before undergoing a DXA test.
Women should always inform their physician and x-ray technologists if there is any possibility that they are pregnant. Many imaging test are not performed during pregnancy so as not to expose the fetus to radiation.
How do I schedule a Bone density scan?
Call the Diagnostic Imaging Scheduling line at 970-870-2399
How is the exam performed?
In the Central DXA examination, like the machine at YVMC, which measures bone density in the hip and spine, the patient lies on a padded table. An x-ray generator is located below the patient and an imaging device, or detector, is positioned above.
To asses the spine, the patient’s legs are supported on a padded box to flatten the pelvis and lower back (spine). To asses the hip, the patient’s foot is placed in a brace that rotates the hip inward. In both cases, the detector is slowly passed over the area, generating images on the computer monitor. The test is usually completed within 10 to 30 minutes.
You will be asked to fill out a questionnaire that will help the doctor determine if you have medial conditions or take certain medications that either increase or decrease your risk of fracture, so bring a list of all medications. The World Health Organization has recently released an online survey that combines the DXA results and a few basic questions and can be used to predict 10-year hip fracture risk for post-menopausal women. This will be coming into more use in the next few years.
The DXA machine sends a thin, invisible beam of low dose x-rays with two distinct energy peaks through the bones being examined. One peak is absorbed mainly by soft tissue and the other by bone. The soft tissue amount can be subtracted from the total and what remains is a patient’s bone mineral density.
Who Should Get Bone Density Testing?
- Bone density testing is strongly recommended 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.
- Use medications that are known to cause bone loss, including corticosteroids such as Prednisone, various anti-seizure medications such as Dilantin and certain 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.
What will I experience during an after the procedure?
Bone density test are a quick and painless procedure.
Who interprets the results and how will I get them?
A radiologist, a physician specifically trained to supervise and interpret radiology examinations, will analyze the images and send a report and copy of the exam to your primary care or referring physician, who will discuss 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 female 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 (low bone mass). 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 the need for further medical tests.
Small changes may normally be observed between scans due to differences in positioning and usually are not significant.
What are the benefits vs. risks?
Benefits
- DXA bone densitometry is a simple, quick and noninvasive procedure.
- No anesthesia is required.
- The amount of radiation used is extremely small-less than one-tenth the dose of a standard chest x-ray, and less than a day’s exposure to the natural radiation.
- DXA bone density testing is the most accurate method of available for the diagnosis of osteoporosis and is also considered an accurate estimator of fracture risk.
- DXA equipment is widely available making DXA bone densitometry testing convenient for patients and physicians alike.
- No radiation remains in your body after the examination.
- X-rays usually have no side effects in the diagnostic range.
Risks
- There is always a slight chance of cancer from excessive exposure to radiation; the effective radiation dose from this procedure is about 0.01 mSv, which is about the same as the average person receives from background radiation in one day.
- No complications are expected with the DXA procedure.
What are the limitations of DXA Bone Densitometry?
- A DXA test cannot predict who will experience a fracture but can provide indications of relative risk.
- Despite its effectiveness as a method of measuring bone density, DXA is of limited use in peo