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What is bone densitometry? |
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Bone densitometry is a way of measuring your bone density, which is a method of estimating the strength of bones and the likelihood of bone fractures with minimal or no trauma. If the bone density is very low, then you have osteoporosis and a very high risk of fracturing your bones. A standard X-ray is not a good way to measure bone density because you must lose at least 30% of your bone mass before it can be detected this way. The doctor and patient needs to find out about any problem long before it gets that severe. There are different techniques for measuring bone density. The "gold standard" method is called "Dual Energy X-ray Absorptiometry" - abbreviated DXA, or DEXA. This uses a very weak form of X-ray (about 1/30 the radiation of a standard chest X-ray) to rapidly scan your bones and a computer to convert this information to numbers indicating your bone density. This is a high technology test which takes only a few minutes and involves no shots, needles, enemas, or medicine. In fact, you don't even have to take off your clothes, provided what you are wearing does not contain any metal objects. |
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Are there different kind of bone densitometry tests? |
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Bone density tests are divided into two types- Central and Peripheral.
Central test measures bone mineral density (BMD) at the spine or hip. This is usually done with DXA technology, which uses a very weak form of X-ray to measure BMD. DXA is generally considered to be the "gold standard" method of measuring BMD for diagnosing osteoporosis and monitoring the effects of osteoporosis therapy. Central testing of the spine can also be done by quantitative computerized tomography (QCT), a specialized type of computerized tomography (CT) scanning that uses larger doses of X-rays.
Peripheral tests measure other skeletal sites, such as the heel, forearm, or shin. These use a variety of technologies, including peripheral DXA (pDXA), quantitative ultrasound (QUS), and peripheral QCT scanning (pQCT). Peripheral tests may be used to estimate the risk of fracture, but the ISCD recommends that they not be used to diagnose osteoporosis or monitor the effects of therapy. |
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Who should have a bone densitometry test? |
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Indications for Bone Mineral Density (BMD) Testing - Anyone who wants an accurate measurement of bone density should have a bone density test. However, because of cost concerns, the test is most often administered for those with high risk of developing osteoporosis, or to monitor the effectiveness of treatment for osteoporosis. Consult with your physician if you think you might benefit from knowing your bone density. The ISCD recommends that a bone density test be done for:
Brtebral changes in Osteoporosis
- All women aged 65 and older.
- Postmenopausal women under age 65 with risk factors.
- All men aged 70 and older.
- Adults with a fragility fracture.
- Adults with a disease or condition associated with low bone mass or bone loss.
- Adults taking medications associated with low bone mass or bone loss.
- Anyone being considered for pharmacologic therapy.
- Anyone being treated, to monitor treatment effect.
- Anyone not receiving therapy in whom evidence of bone loss would lead to treatment.
Women discontinuing estrogen should be considered for bone density testing according to the indications listed above.
Reference Database for T-scores :
- Use a uniform Caucasian (non-race adjusted) female normative database for women of all ethnic groups.
- Use a uniform Caucasian (non-race adjusted) male normative database for men of all ethnic groups.
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How do i know if i have osteoporosis? |
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CLose Up View
There are two ways of making a diagnosis of osteoporosis:
A DXA test of the spine, hip, or forearm shows a T-score equal to or less than -2.5. The T-score is a mathematical method for comparing your bone density to that of a healthy person of the same sex in their twenties. A T-score of zero is normal. The lower the T-score, the lower your bone density, the weaker your bones, and the more likely they are to break.
A "fragility fracture" has occurred. This is a broken bone that has happened with no trauma or minimal trauma, such as falling to the floor from the standing position.
Clearly, it is better to find out if you have osteoporosis by measuring your bone density BEFORE a fracture occurs so that treatment can be started to lower your risk of fracture. But even if you have already had an osteoporotic fracture, treatment can lower your risk of having another. |
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When should a bone densitometry test be repeated? |
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In order to determine the best time to repeat a bone density test, it is necessary to know the expected rate of change in bone density and the precision of the instrument being used to perform the test. In some situations, such as starting high dose glucocorticoid therapy, such as prednisone, a test may be done as often as every six months. After starting a medication for osteoporosis, it may take one or two years before a significant change in bone density has occurred. If bone density is changing very little, then three to five years or longer may be appropriate. |
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Will insurance pay for bone densitometry test? |
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It depends. At this time, most insurance companies have a very specific list of diagnoses that will qualify you for coverage to have bone densitometry done. The list is different for each type of insurance and often pre-authorization is required before the test is scheduled. Your physician's office can give you more information on whether or not you will be covered. If you and your physician feel that the test should be done, even if not covered by insurance, then arrangements can be made for self-pay at a discounted rate.
Medicare will cover a bone density test for the following situations:
- Estrogen deficient women undecided about taking hormones.
- Those with spinal abnormalities or X-ray evidence of bone loss.
- Anyone taking long-term corticosteroid treatment (such as prednisone).
- Primary hyperparathyroidism with no symptoms.
- Monitoring of therapy for osteoporosis.
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What are some common uses of the procedure? |
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DEXA bone densitometry 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 test can also assess your risk for developing fractures. If your bone density is found to be low, you and your physician can work together on a treatment plan to help prevent fractures before they occur. DEXA is also effective in tracking the effects of treatment for osteoporosis or for other conditions that cause bone loss. 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 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 experienced a fracture after only mild trauma.
- Have had x-ray evidence of vertebral fracture or other signs of osteoporosis.
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How should I prepare for the procedure? |
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On the day of the exam eat normally, but don't take calcium supplements for at least 24 hours beforehand. Wear loose, comfortable clothing, avoiding garments that have zippers, belts or buttons made of metal.
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 radioisoe scan; you may have to wait 10 to 14 days before undergoing a DEXA test. Women should always inform their physician or x-ray technologist if there is a possibility they are pregnant. |
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What does the DEXA equipment look like? |
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There are two types of DEXA equipment: the central device and the peripheral device. Central DEXA devices measure bone density in the hip and spine, while peripheral devices measure it in the wrist, heel or finger. The central DEXA device is used in hospitals and medical offices, while the smaller peripheral device is available in drugstores and on mobile health vans in the community. CT scanners also can be used effectively to evaluate the spine and hip for osteoporosis.
Central devices have a large, flat table and an "arm" suspended overhead. The arm swings away so that the table can be used as a treatment table or exam chair for routine patient examinations. The peripheral DEXA (pDEXA) device weighs only about 60 pounds. It is a portable box-like structure that includes a space to insert your foot or forearm for imaging. |
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How does the procedure work? |
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The DEXA machine sends a thin, invisible beam of low-dose x-rays with two distinct energy peaks through your bones. 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.
All devices feature special software to compute the data and display them on a computer monitor, allowing your doctor to make an accurate diagnosis. The amount of radiation used is extremely small—less than one-tenth the dose of a standard chest x-ray. |
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How is the procedure performed? |
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The DEXA bone density test takes 10 to 30 minutes, depending on the equipment used and the parts of the body being examined. You may be asked to undress and put on a hospital gown. Then you'll lie on a padded table with an x-ray generator below and a detector (an imaging device) above.
Most often, doctors focus on bone loss in the spine and hip where most osteoporosis-related fractures happen. During an examination of the spine, your legs will be supported on a padded box to flatten your pelvis and lower (lumbar) spine. To assess your hip, the technologist will place your foot 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.
The peripheral DEXA (pDEXA) test is even simpler. You place your finger, hand, forearm or foot in a small device, and a bone density reading is obtained within a few minutes. These tests may not be as sensitive—especially in younger people—and cannot be used to monitor response to treatment.
Lateral Vertebral Assessment (LVA)
An additional procedure called Lateral Vertebral Assessment (LVA) is now being done at many centers. This is a low dose x-ray examination of the spine to screen for vertebral fractures. It is performed on the DEXA machine. Vertebral fractures are common in older individuals and may indicate increased risk for additional fractures if they are present. They are often asymptomatic. The test is painless and adds only a few minutes to the DEXA procedure. It may be recommended for older patients, especially if they have lost more than an inch of height, have unexplained back pain, or if the DEXA scan gives borderline readings and the increased risk if the patient has evidence of fracture would influence the decisions in regard to treatment. |
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What will I experience during the x-ray procedure? |
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DEXA bone densitometry is a simple, non-invasive procedure. Once on the table you may be asked to hold an awkward position for a short time while the arm of the machine passes over your body taking measurements. It is important that you stay as still as possible during the procedure to ensure a clear, useful image. No anesthesia is required. The procedure is painless and radiation exposure is minimal. |
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Who interprets the results and how do I get them? |
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Your Bone densitometry scan is interpreted by a panel of highly qualified and experienced radiologists (see our doctors). After your visit for a diagnostic imaging procedure, the images from your exam are transferred to one of our radiologists who specializes in analyzing images of the specific area of the body you had examined. Next, the radiologist prepares a diagnostic report to share with the doctor that sent you to us. We retains exam films and reports electronically for a set length of time. Please contact our reception counter after your diagnostic imaging procedure if you have questions regarding the timings and procedure for collecting the reports or next steps or follow-up appointments. New technology also allows us for distribution of diagnostic reports and referral images over the Internet at many facilities. Our radiologists have established themselves as valued consultants and colleagues with our referring physicians. They are available 24X7 days for emergency interpretations. They pride themselves on being accessible and responsive. Usually available within few hours (unless emergency case), 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. It 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 it is unusually high or low, it may indicate a need for further medical tests. |
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What are the positive and negative aspects of the study? |
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Positive aspects
DEXA bone density testing is the most accurate method available for the diagnosis of osteoporosis. It is also considered an accurate estimator of fracture risk. It will not tell whether you will or will not have a fracture, but gives relative risk of suffering a fracture, just as cholesterol and blood pressure help determine risk for heart disease. A low reading should not cause you to be anxious but may help you set healthy goals. As with other diseases and conditions, early detection is the key to prevention of further bone loss and eventual fractures. DEXA equipment is widely available making DEXA bone densitometry testing convenient for patients and doctors alike.
Negative aspects
No known complications are expected with the DEXA procedure. |
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What are the limitations of DEXA Bone Densitometry? |
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Despite its effectiveness as a method of measuring bone density DEXA is of limited use in people with a spinal deformity or those who have had previous spinal surgery. The presence of vertebral compression fractures or osteoarthritis may interfere with the accuracy of the test. CT scans may be more useful in such instances. DEXA cannot predict who will experience a fracture but can provide indications of relative risk.
Central DEXA devices are more sensitive than pDEXA devices but they are also somewhat more expensive. The peripheral devices don't accurately follow changes in your bones during therapy. A test done on a peripheral location, such as your heel or wrist, may help predict the risk of fracture in your spine or hip. But because bone mass tends to vary from one location to the other, measuring the heel is not as accurate as measuring the spine or hip. Small changes may normally be observed between scans due to differences in positioning and may not be significant. As with mammograms, the examination must be done with great care to maximize accuracy. |
