|What a Bone Mineral Density (BMD) test can do?
Bone mineral density (BMD) test uses a special machine a DEXA scan to measure your bone density to see if you are at risk for osteoporosis. The test results lets you know the health of your bones and the amount of bone mineral you have in a certain area of bone, including your hip, spine, forearm, wrist, finger, or heel. The test takes about 15 to 20 minutes to perform and is very safe and painless.
Your BMO results are reported as a T score and compared to 30 year old :
Normal – Bone density is within 1 SO (+1 or -1) of the young adult mean.
Low bone mass Osteopenia – Bone density is between 1 and 2.5 SO below the young adult mean (-1 to -2.5 SO).
Osteoporosis – Bone density is 2.5 SO or more below the young adult mean (-2.5 SO or lower).
Severe (established) osteoporosis – Bone density is more than 2.5 SO below the young adult mean, and there have been one or more osteoporotic fractures.
Who Should Have a BMD Test?
There are some reasons (called risk factors) that increase your likelihood of developing osteoporosis. The more risk factors you have, the more likely you are to get osteoporosis and broken bones. Some examples are being small and thin, older age, being female, a diet low in calcium, lack of enough vitamin D, smoking and drinking too much alcohol.
Your healthcare provider may recommend a BMD test if you are:
- A postmenopausal woman under age 65 with one or more risk factors for osteoporosis
- A man age 50-70 with one or more risk factors for osteoporosis
- A woman age 65 or older, even without any risk factors
- A man age 70 or older, even without any risk factors
- A woman or man after age 50 who has broken a bone
- A woman going through menopause with certain risk factors
- A postmenopausal woman who has stopped taking estrogen therapy (ET) or hormone therapy (HT)
Some other reasons your healthcare provider may recommend a BMD test:
- Long-term use of certain medications including steroids (for example, prednisone and cortisone), some anti-seizure medications, Depo-Provera® and aromatase inhibitors (for example, anastrozole, brand name Arimidex®)
- A man receiving certain treatments for prostate cancer
- A woman receiving certain treatments for breast cancer
- Overactive thyroid gland (hyperthyroidism) or taking high doses of thyroid hormone medication
- Overactive parathyroid gland (hyperparathyroidism)
- X-ray of the spine showing a fracture or bone loss
- Back pain with a possible fracture
- Significant loss of height
- Loss of sex hormones at an early age, including early menopause
- Having a disease or condition that can cause bone loss (such as rheumatoid arthritis or anorexia nervosa)
Types of Bone Density Tests
Central DXA: The National Osteoporosis Foundation (NOF) recommends a BMD test of the hip and spine by a central DXA machine to diagnose osteoporosis. DXA stands for dual energy x-ray absorptiometry. When testing can’t be done on the hip and spine, NOF suggests a central DXA test of the radius bone in the forearm. In some cases, the type of bone density testing equipment used depends on what is available in your community.
Healthcare providers measure BMD in the hip and spine for several reasons. First, people with osteoporosis have a greater chance of fracturing these bones. Second, these fractures can cause more serious problems, including longer recovery time, greater pain and even disability. BMD test results in the hip and spine can predict the likelihood of future fractures in other bones.
With most types of BMD tests, a person remains fully dressed, and the test usually takes less than 15 minutes. BMD tests are non-invasive, meaning that no needles or instruments are placed through the skin or body. When repeating a BMD test, it is best to use the same testing equipment and have it done at the same place. This provides a more accurate comparison with your last test result.
Although it is not always possible to have your BMD test at the same place, it is still important to compare your current BMD test to your last one.
Other Types of Tests:
In addition to central DXA, there are other methods to measure bone density that can predict the risk of breaking a bone. However, the results from these other methods are not equivalent to the results from a central DXA machine. Below are other BMD testing methods:
- pDXA (peripheral dual energy x-ray absorptiometry)
- QUS (quantitative ultrasound)
- QCT (quantitative computed tomography)
- pQCT (peripheral quantitative computed tomography)
The QUS method of BMD testing uses sound waves to measure bone density. The other types of equipment listed above use radiation. Except for QCT, the amount of radiation is very small. For comparison, you are exposed to 10–15 times more radiation flying in a plane round trip between New York and San Francisco.
Healthcare providers do not routinely use standard x-rays for BMD testing. While x-rays can identify broken bones, they are not sensi-tive enough to detect osteoporosis until 25 to 40 percent of bone density has been lost. By this time the disease is well advanced.
Peripheral bone mineral density tests help identify people who are most likely to benefit from further BMD testing. This type of test is often done as a screening at health fairs and in some medical offices, but cannot be used to accurately diagnose osteoporosis. Peripheral BMD tests measure BMD in the extremities, including the forearm, wrist, finger or heel. This BMD testing method uses pDXA, QUS and pQCT. People having a peripheral test should be aware that there are some limitations with this type of test. Comparisons between a peripheral test and a DXA test of the hip and/or spine may not be reliable. Peripheral tests are suitable for screening and predicting the risk of fractures. Experts prefer the central DXA test for diagnosing osteoporosis and monitoring treatment in patients taking an osteoporosis medication. If you have abnormal results from a peripheral BMD screening, you should follow up with your healthcare provider. Discuss whether you need additional testing, such as a central DXA test of the hip and/or spine.
People of Larger Size
Most central DXA machines cannot measure BMD in the hip and spine of patients who weigh over 300 pounds. Some newer machines can measure BMD in people who weigh up to 400 pounds, but they are not widely available.
When the hip and spine cannot be measured, a central DXA test can often measure BMD of the radius bone in the forearm to diagnose osteoporosis. If this can’t be done, another option is a peripheral BMD test of another extremity, such as the heel or wrist.
For people of larger size, some healthcare providers recommend having both a central DXA test of the forearm and a peripheral test of the heel or other bone. Doing both of these tests provides more complete information.
How Often to Repeat a BMD Test
People taking an osteoporosis medication should repeat their BMD test by central DXA every two years, according to the National Osteoporosis Foundation (NOF). Some healthcare providers may have certain patients repeat their BMD test after one year. The peripheral tests (pDXA, QUS and pQCT) are not appropriate for monitoring response to treatment at this time.
Tests to Find Broken Bones
If you have a loss of height, posture changes or back pain, your healthcare provider may order an x-ray to look for fractures in your spine. An x-ray is the most common way to tell if you have a broken bone in your spine or other bones. In some people, spine fractures don’t cause any pain.
Once you have a fracture in the spine, you are at greater risk for more spine fractures in the future. If you have this type of fracture, that’s why you need to speak with your healthcare provider about steps to protect your spine. You should also consider treatment with an osteoporosis medication. When you have a fracture in the spine, you still need to have a BMD test if you haven’t had one.
Another way to find fractures in the spine is with a vertebral fracture assessment (VFA) by a DXA machine. This method uses less radiation than a standard x-ray. VFAs can show breaks in the spine and can also show the difference between broken bones and abnormally shaped bones.
Understanding BMD Test Results
When you have a bone mineral density test, it compares your bone density to a “young normal” healthy 30-year-old adult with peak bone density (also called peak bone mass). Peak bone density is the point at which a person has the greatest amount of bone that she or he will ever have.
You will get the result of your BMD test in a special number called a T-score. It stands for “standard deviations” or “SD.” It indicates how much your bone density is above or below normal.
Healthcare providers use the T-score to diagnose osteoporosis. If more than one bone is tested, they use the lowest T-score to make a diagnosis of osteoporosis. The World Health Organization (WHO) has defined the T-scores and what they mean.
What your T-score means:
- A T-score between +1 and -1 is normal bone density. Examples are 0.8, 0.2 and -0.5.
- A T-score between -1 and -2.5 indicates low bone density or osteopenia. Examples are T-scores of -1.2, -1.6 and -2.1.
- A T-score of -2.5 or lower is a diagnosis of osteoporosis. Examples are T-scores of -2.8, -3.3 and -3.9.
The lower a person’s T-score, the lower the bone density. A T-score of -1.0 is lower than a T-score of 0.5; a T-score of -2.0 is lower than a T-score of -1.5; and a T-score of -3.5 is lower than a T-score of -3.0. For most BMD tests, 1 SD difference in a T-score equals a 10-15 percent decrease in bone density. For example, a person with a T-score of -2.5 has a 10-15 percent lower BMD than a person with a T-score of -1.5.
Your BMD test result also includes a Z-score that compares your bone density to what is normal in someone your age and body size. Healthcare providers do not use Z-scores to diagnose osteoporosis in postmenopausal women and men age 50 or older. Among older adults low bone mineral density is common, so Z-scores can be misleading. An older person might have a “normal” Z-score but still be at high risk for breaking a bone.
Most experts recommend using Z-scores rather than T-scores for younger men, premenopausal women and children. However, healthcare providers often use
T-scores for perimenopausal women. A Z-score above -2.0 is normal according to the International Society for Clinical Densitometry (ISCD). A diagnosis of osteoporosis in younger men, premenopausal women and children should not be based on a BMD test result alone. NOF does not recommend routine BMD testing in children, adolescents, healthy young men or premenopausal women.
When to Consider Treatment
The results of the BMD test help your healthcare provider make recommendations about either prevention or treatment of osteoporosis. When making a decision about treatment with an osteoporosis medication, your healthcare provider will also consider your risk factors for osteoporosis, your likelihood of having future fractures, your medical history and your current health.
Below are treatment guidelines for postmenopausal women and men age 50 or older:
- Most people with T-scores of -1 and above (normal bone density) do not need to take an osteoporosis medication.
- People with T-scores between -1 and -2.5 (osteopenia) should consider taking an osteoporosis medication when they have certain risk factors.
- All people with T-scores of -2.5 and below (osteoporosis) should consider taking an osteoporosis medication.
A new method called absolute fracture risk helps healthcare providers and their patients age 40 and older make better decisions about when to take an osteoporosis medication. Absolute fracture risk estimates a person’s chance of breaking a bone over a period of 10 years. Postmenopausal women and older men with osteoporosis are at greatest risk of breaking a bone.
In the past, healthcare providers knew to treat people with osteoporosis, but were sometimes uncertain about when to treat patients with osteopenia. The absolute fracture risk method makes it easier for healthcare providers and their patients with osteopenia to decide when an osteoporosis medication is necessary. This method helps make sure that people with the greatest chance of breaking a bone get treated.
Healthcare providers can get a patient’s absolute fracture risk by using a special web-based tool on a computer in their office. The healthcare provider enters a patient’s hip T-score and certain risk factors for osteoporosis. The tool predicts the patient’s absolute fracture risk. Soon, some central DXA machines will be able to provide this information.
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