Definition:A bone density test uses special X-rays to measure how many grams of calcium and other bone minerals are packed into a segment of bone.It measure the thickness and strength of your bones. Various scanners use different techniques, such as dual-energy x-ray absorptiometry (DXA) and radiographic absorptiometry. Quantitative ultrasound, which does not involve x-rays, may also be used.
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When bones are somewhat thin, the condition is called osteopenia; when bones become very thin, the condition is called osteoporosis. Bone density tests provide a precise measure of whether you have osteopenia or osteoporosis.Men, and particularly women, usually begin to lose bone thickness around age 50. Exercise and various treatments can help prevent and even restore bone loss; that’s why diagnosing thin bones is important.Many authorities now recommend screening for thin bones. Not only is this test used to help detect osteoporosis, but it is also helpful in monitoring your progress if you’re taking bone-building medications.
A bone density test is a fairly accurate predictor of your risk. The results from a bone density test can let you know how you compare with other people of your age, sex and other similar characteristics.
Why it is required?
The higher your mineral content, the denser your bones are. And the denser your bones, the stronger they generally are and the less likely they are to break.
Doctors use a bone density test to determine if you have, or are at risk of, osteoporosis.
Bone density tests are not the same as bone scans. Bone scans require an injection beforehand and are usually used to detect fractures, cancer, infections and other abnormalities in the bone.
The U.S. Preventive Services Task Force recommends routine bone density screening if:
You’re a woman age 65 or older
You’re 60 and at increased risk of osteoporosis
Research hasn’t yet determined the optimal interval for repeat bone density screenings, or the right age to stop screening. However, two or more years may be needed between tests to reliably measure a change in your bone density. Your doctor can recommend the best screening interval for you based on your personal medical history and osteoporosis risk factors.
The older you get, the higher your risk of osteoporosis because your bones become weaker as you age. Your race also makes a difference: you’re at greatest risk of osteoporosis if you’re white or of Southeast Asian descent, and African American and Hispanic men and women have a lower, but still significant, risk. Other risk factors for osteoporosis include low body weight, a personal history of fractures, a family history of osteoporosis and using certain medications that can cause bone loss.
The test doesn’t have any significant risks. Bone density tests that use x-rays expose you to about one-tenth the amount of radiation as in a single chest x-ray; this is too small an amount to be likely to cause any harm, except to a fetus in a pregnant woman.
Bone density testing is a valuable tool in the diagnosis of osteoporosis and is a fairly accurate predictor of your risk of fractures. Significant differences in the various testing methods do exist, however. Central devices are more accurate, but cost significantly more than peripheral devices do.
Not all health insurance plans cover bone density tests, so ask your insurance provider whether it provides coverage that applies to your situation.
A bone density test can confirm that you have low bone density, but it can’t tell you why. To answer that question, you need a complete medical evaluation, including a history and physical. This information can help your doctor better interpret the results of the bone density test.
How do you prepare for the test?
Bone density tests are easy, fast and painless. Virtually no preparation is needed. In fact, some simple versions of the bone density tests can be done at your local pharmacy or drugstore.
If you’re having the test done at a medical center or hospital, be sure to tell your doctor beforehand if you’ve had recent oral contrast or nuclear medicine tests. These tests require an injection of radioactive tracers that might interfere with your bone density test.
Be sure to tell your doctor if you might be pregnant. A screening test that uses x-rays can’t be performed during pregnancy because it may increase the risk of birth defects.
What happens when the test is performed?
Bone density tests can be done in the radiology department of a hospital, a radiology diagnostic center, or a doctor’s office.You lie on a table that has an overhanging cover, resembling a tanning bed, while a radiologist or x-ray technician moves a scanner above your spine, hip, or wrist. The test takes 10-20 minutes. The test itself is painless, but you may experience some discomfort because you have to lie still.
The equipment for bone density tests includes large machines on which you can lie down (central devices) as well as smaller, portable machines that measure bone density on the periphery of your skeleton, such as in your finger, wrist or heel (peripheral devices).
*DEXA scan. Dual energy X-ray absorptiometry (DEXA) scans measure the bone density at your hip or spine. This test offers very precise results and is the preferred test for diagnosing osteoporosis. During this test, you lie on a padded platform for a few minutes while an imager — a mechanical arm-like device — passes over your body. It won’t touch you. The test does, however, emit radiation, though your exposure during a bone density test is commonly about one-tenth of the amount emitted during a chest X-ray. This test usually takes five to 10 minutes to complete.
*Quantitative CT scan. This test uses a computerized tomography (CT) scanner combined with computer software to determine your bone density, usually at your spine. Quantitative CT (QCT) scans provide detailed, 3-D images and can take into account the effects of aging and diseases other than osteoporosis on your bones. QCT scans emit more radiation than DEXA scans do. For a QCT test, you lie on a movable table that’s guided into a large tube-like area where images are taken. It typically takes less than 10 minutes.
Peripheral devices are found in pharmacies and are considerably less expensive than are central devices. But these smaller machines do have limitations.
Measurements taken at your hip and spine generally are considered more accurate assessments of your osteoporosis risk because these are the locations where major fractures tend to occur — fractures that can severely limit the quality and even the length of your life.
A test done on a peripheral location, such as your heel, may predict risk of fracture in your spine and hip as well. But because bone density tends to vary from one location to the other, a measurement taken at the heel usually isn’t as accurate as a measurement taken at the spine or hip.
Measurements of bone density in your heel or finger still can be used to screen for osteoporosis, though. If your test is positive, your doctor might recommend a DEXA scan at your spine or hip to confirm your diagnosis.
How long is it before the result of the test is known?
You’ll get the results within a few days. The results will include two scores, the T-score and the Z-score. The T-score measures your bone density compared with the average values in young adults of the same race and sex. The Z-score shows how your bone density compares with that of people your own age, race, and sex. A positive T-score means your bones are stronger than the average in a young adult, and a negative score means that your bones are weaker. If you have a T-score that is between -1.0 and -2.5, you have osteopenia. If it is below -2.5, you have osteoporosis.
In general, the lower your bone density, the higher your risk of breaking a bone. Fractures of the hip are particularly disabling, and fractures of the spine are common and painful. Bone density measured at the hip and spine by DXA is regarded by most experts as the best predictor of hip and spine fracture. DXA also is excellent for diagnosing thin arm bones; wrist fractures occur more easily in people with osteopenia or osteoporosis. Fortunately, treatment options exist. Talk with your doctor.
Anything Must you do special after the test is over?