A bone density test (also known as bone mass measurement), measures the strength and density of the bones. The measurements are used to determine decreased bone mass, which causes the bones to be more brittle and more prone to break or fracture easily.
Bone density testing can help to detect low bone density before a fracture occurs and they can confirm a diagnosis of osteoporosis if you have already fractured a bone. Osteoporosis is the decrease of bone mass and density due to the depletion of calcium and protein in the bones.
The testing may be done using X-rays or by CT scanning using special software to determine bone density of the hip or spine. The procedure is usually done in a clinic, hospital or radiology facility, but portable types of testing can also be done.
About the procedure: The patient is positioned on an X-ray table, lying flat. Under the table, a photon generator will pass slowly beneath the patient, while an X-ray detector camera passes above the table, parallel to the photon generator beneath, projecting images of the lumbar and hip bones onto a computer monitor. The procedure will be repeated to obtain images of other bone areas. The computer will calculate the amount of photons that are not absorbed by the bones to determine the mineral content of the bones. The radiologist will then calculate the bone mineral density.
- Bone density tests are painless, noninvasive and safe. There may be some discomfort during manipulation of the body, especially if a patient has a recent injury.
- Generally, no prior preparation is needed, but patients may be asked to stop taking calcium supplements 24 to 48 hours prior to the test.
- Because radiation is involved, it should not be performed if the patient is pregnant.
- Physician referral form
- Current medical insurance card
- Driver’s license or other government-issued identification
- Wear comfortable clothing. (Avoid metal straps, buttons, zippers)
Bone densitometry scanning, also called dual-energy x-ray absorptiometry (DXA or DEXA) or simply a "bone density scan," 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 densitometry.
An x-ray (radiograph) is a painless medical test that helps physicians diagnose and treat medical conditions. Radiography involves exposing a part of the body to a small dose of ionizing radiation to produce pictures of the inside of the body. X-rays are the oldest and most frequently used form of medical imaging.
Bone densitometry is most often performed on the lower spine and hips.
Bone densitometry is most often used to diagnose osteoporosis, a condition that most often affects women after menopause. Osteoporosis involves a gradual loss of calcium, causing the bones to become thinner, more fragile, and more likely to break.
The exam is 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.
Bone densitometry 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 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, a low-dose x-ray examination of the spine to screen for vertebral fractures that is performed on the DEXA machine, may be recommended for older patients, especially if you:
- Have lost more than an inch of height.
- Have unexplained back pain.
- Have had a bone densitometry scan that gave borderline readings.
Special care is taken during x-ray examinations to use the lowest radiation dose possible while producing the best images for evaluation. National and international radiology protection councils continually review and update the technique standards used by radiology professionals.
State-of-the-art x-ray systems have tightly controlled x-ray beams with significant filtration and dose control methods to minimize stray or scatter radiation. This ensures those parts of a patient's body not being imaged receive minimal radiation exposure.
- Food and drink: On the day of your bone densitometry scan you may eat normally. You should not take calcium supplements for at least 24 hours before your exam.
- When to arrive: Arrive 15 minutes before your scheduled appointment time to check in and fill out any necessary forms.
- What to wear: 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. You may also be asked to remove jewelry, eyeglasses, and any metal objects or clothing that might interfere with the x-ray images.
- Other information: Inform your physician 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 physician or technologist if there is any possibility that they are pregnant. Many imaging tests are not performed during pregnancy because radiation can be harmful to the fetus. If an x-ray is necessary, precautions will be taken to minimize radiation exposure to the baby.
- Scanning: Bone densitometry scans are a quick and painless procedure, and usually done on an outpatient basis. You will lie on a padded table. An x-ray generator will be located below you and an imaging device, or detector, will be positioned above.
To assess your spine, your legs will be supported on a padded box to flatten the pelvis and lower (lumbar) spine. To assess the hip, your foot will be placed in a brace that rotates the hip inward. In both cases, the detector will slowly pass 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 picture is taken to reduce the possibility of a blurred image.
- Length of scan: The scan is usually completed within 20 to 30 minutes.
Instructions: You may resume normal activity immediately after your bone densitometry scan.
Exam results: All bone densitometry exams are interpreted by a radiologist. Under normal circumstances the reports are available electronically to the ordering physician within 24 hours. Your referring physician will communicate these results to you.