What is a Bone Density Scan?
Bone density scanning, also called DEXA or bone densitometry, is an enhanced form of x-ray technology that is used to measure bone loss. DEXA is today's established standard for measuring bone mineral density (BMD).
DEXA is most often performed on the lower spine and hips.
DEXA 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, as well as structural changes, causing the bones to become thinner, more fragile and more likely to break.
DEXA is also effective in monitoring the effects of treatment for osteoporosis and other conditions that cause bone loss.
The DEXA test can also assess an individual's risk for developing fractures. The risk of fracture is affected 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. These factors are taken into consideration when deciding if a patient needs therapy.
Bone density testing is strongly recommended if you:
- Are a post-menopausal woman and not taking estrogen.
- Have a family history of osteoporosis.
- Are a Smoker.
- Have a personal or maternal history of hip fracture.
- Are a post-menopausal woman who is tall (over 1.75 meter) or thin (less than 57 kilogram).
- Use medications that are known to cause bone loss, including corticosteroids, various anti-epileptic medications or high-dose thyroid replacement drugs.
- Have type 1 diabetes, liver disease or kidney disease 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.
- Are a man with clinical conditions associated with bone loss.
Routine evaluations every two years may be needed to evaluate any significant increase or decrease in bone mineral density. Some patients, such as patients on high dose steroid medication, may need follow-up at six months.
How should I prepare for a bone density scan?
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 clothes and to wear a gown during the exam.
Inform your physician and radiology department if you recently had a barium examination 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 a DEXA test.
Women should always inform their doctor or radiographer if there is any possibility that they are pregnant.
How is the bone density scan performed?
This examination is usually done on an outpatient basis.
The DEXA machine has a large, flat table and an "arm" suspended overhead. An x-ray generator is located below the patient and an imaging device, or detector, is positioned above.
The DEXA 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 DEXA machine feature special software
that compute and display the bone density measurements on a computer monitor.
The patient will lie flat on the padded bed. To assess the spine, the patient's legs are elevated and supported on a padded cushion to flatten the pelvis and lower (lumbar) spine. To assess 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 a computer monitor.
You must hold very still and may be asked to keep from breathing for a few seconds while the x-ray picture is taken to reduce the possibility of a blurred image.
An additional procedure called Lateral Vertebral Assessment (LVA) will also be done. LVA is a low-dose x-ray examination of the spine to screen for vertebral fractures and is also performed on the DEXA machine. The LVA test adds only a few minutes to the DEXA procedure.
The radiologist will analyze the images and prepare a signed report for 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 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 a need for further medical tests.
Small changes may normally be observed between scans due to differences in positioning and usually are not significant.
The DEXA bone density test is usually completed within 30 – 60 minutes.
What will I experience during and after the bone density scan?
Bone density tests are a quick and painless procedure.
What will a bone density scan cost?
Most medical aids will cover the cost of a bone density scan provided that you have not exceeded your annual imaging limit. Pre-authorization is usually not required by medical aids, but please consult with your medical aid if you are uncertain.
Private patients who pay immediately with cash or with Master or Visa Cards will be charged medical aid rates.
The account remains your responsibility.
In the event of non – payment by your medical aid, you will be held liable for the account and it should be paid within 30 days.