DXA (dual energy X-ray absorptiometry): The DXA measurement technique is the most accurate and precise measurement of your bone mineral density. At present it is the gold standard technique throughout the world and used in all major trials of new treatments for the prevention or treatment of osteoporosis. The standard test is on the hip regions and the spine, with addition or substitution of a forearm measurement in some cases.
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The measurement at the hip and spine regions is chosen for several reasons. Firstly, people with osteoporosis have a greater chance of fracturing these bones and secondly such fractures can cause more serious problems, including long recovery time, greater pain and even disability. BMD test results in the hip and spine can predict the likelihood of future fractures not only in these bones, but also in other bones throughout your skeleton.
DXA bone density tests are non-invasive meaning that no needles or instruments are placed through the skin or body. You can remain fully dressed and the tests, including you answering an important clinical questionnaire usually take no more than 30 minutes. A repeat bone density using the same testing equipment and at the same branch will provide the most accurate comparison with your last test result. However, this is not always possible and the accuracy of the machines at all the Auckland Bone Density branches is checked for comparability once yearly. Reasonable comparisons can be made however with the measurements from other machines from other providers.
The reporting specialists have access to your referral letter, questionnaire and the detailed scan images and data. Whilst you will not meet your reporting specialist, all this information results in a "virtual" consultation and advice back to your referring doctor.
What the results mean?
People frequently have osteoporosis with no signs or symptoms. However, when you have osteoporosis, your bones become weaker and are more likely to break. Early diagnosis can make a difference because it is a disease that can be prevented and treated. At any age, it is never too late to take steps to protect your bones and prevent fractures. Any fracture of bones other than fingers, toes, face and skull that has occurred as a result of only a minor accident (e.g., a fall from no more than standing height) is frequently due to underlying bone weakness, i.e., osteoporosis.
You can find out whether you have osteoporosis or if you should be concerned about your bone health by getting a Bone Mineral Density (BMD) Test. A BMD test uses a special machine to measure bone density, which some people also call a bone mass measurement test. Accurate bone density testing can be done on different bones of your body, including your hip regions, lower spine and forearm. A BMD test is safe and painless and lets you know the bone mineral you have in a certain area of bone. This provides important information about bone health and your health provider can use this information to make recommendations to help you protect your bones, and reduce fracture risk. If you are diagnosed with osteoporosis, your doctor may order laboratory and other tests which can help find out if you have another medical condition causing bone loss.
What a BMD Test can do?
A BMD test is the only way to detect low bone density and diagnose osteoporosis. The lower a person’s bone density, the greater the risk of having a fracture. The BMD test results are used to:
Detect low bone density before a person breaks a bone.
Predict a person’s chance of breaking a bone in the future.
Establish osteoporosis as the cause, when a person has already broken a bone.
Determine whether an individual’s bone density is increasing, decreasing or remaining the same.
Monitor a person’s response to treatment.
Who should have a BMD test?
Certain risk factors increase the likelihood of you developing osteoporosis. The more risk factors you have, the more likely you are to get osteoporosis and broken bones. Important examples are being small and thin, older age, being female, lack of enough vitamin D, low dietary calcium, and immediate family history of osteoporosis (especially parents, brother or sister), smoking and excessive alcohol intake (3 or more drinks per day).
The following are common reasons for a BMD test being desirable:
A postmenopausal woman under age 65 with one or more risk factors.
A woman aged 65 or older, even without any risk factors.
A man aged 50-70 with one or more risk factors for osteoporosis.
A man age 70 or older, even without any risk factors.
Any man or woman after age 50 who has broken a bone.
A woman going through an early menopause who has risk factors.
A postmenopausal woman who has stopped taking hormone replacement therapy (HRT).
There are other reasons that your doctor may recommend a BMD:
A woman receiving certain treatments for breast cancer, e.g., Arimidex (anastrozole) and Femara (Letrozole).
A man receiving certain treatments for prostate cancer (anti-androgen therapy).
Long term use of certain medications including prednisone and hydrocortisone, some anti-epilepsy medications, and Depo-Provera.
Excessive doses of thyroid hormone (Thyroxine), or an overactive thyroid gland (hyperthyroidism).
Loss of sex hormones at an early age, including early menopause.
X-ray of the spine showing a fracture or some bone loss.
Back pain with possible fracture.
Significant loss of height.
Having a disease or condition that can cause bone loss, such as rheumatoid arthritis, anorexia nervosa, and coeliac disease
Screening tests are sometimes available in pharmacies, shopping malls, health fairs, etc. These cannot be used to accurately diagnose osteoporosis, but are helpful in identifying people who are most likely to benefit from further BMD tests. People having a peripheral test of this type should be aware that there are some limitations with this type of testing and comparisons between such results and a DXA test of the hip and spine may not be reliable. If you have abnormal results from a peripheral BMD screening test, you should follow this up with your doctor and discuss whether you need additional testing such as central DXA testing of the hip and spine. Experts worldwide prefer the central DXA test for diagnosing osteoporosis and for monitoring treatment results in patients taking an osteoporosis medication.
People of larger size
Most central DXA machines cannot measure the BMD in the hip and spine of patients who weigh over 150kg. However, when the hip and spine cannot be measured as a result, a measurement of the forearm bones can be helpful in the diagnosis of osteoporosis.
Where can you have a BMD test?
Auckland Bone Density provides central DXA bone density measurements at 5 sites around the Auckland Region.
It is preferable, but not essential to have a referral from your own doctor. If this is not possible, we will, with your permission report not only to you, but also to your regular doctor.
How often to repeat a BMD test?
It is advisable for people taking an osteoporosis medication to repeat their bone density test by central DXA at intervals determined by the reporting specialist. However, in some situations such as steroids etc (prednisone, hydrocortisone), measurements may need to be repeated as frequently as each year. Monitoring of the natural bone loss as we age may be quite infrequent but our specialists will recommend an appropriate interval for each person.
Tests to find broken bones
If you have experienced loss of height, unexplained posture changes, or back pain, your doctor 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 (vertebra) in your spine or of other bones. Pain is not an essential symptom, since about 50% of spine fractures do not cause pain, as they can happen very slowly.
However, once you have a documented fracture in the spine, you are at much greater risk for more spine fractures in the future. Identification of any spinal fracture should prompt you to speak with your doctor about the steps to protect your spine in the future. This may also include osteoporosis medications, if osteoporosis is confirmed on DXA testing.
The machine at our Epsom site has the ability to find fractures in the spine with a vertebral fracture assessment, which uses less radiation than a standard X-ray and it can also show the difference between broken vertebral bones and abnormally shaped vertebrae.
Understanding DXA BMD test results
When you have a bone density test, your bone density becomes compared with a “young normal” healthy 30-year old adult, of your same sex. At this age, we achieve our maximum bone density, called peak bone density or peak bone mass. You will get the result of your BMD test in a special number called a T-score, which indicates how much your bone density is above or below the peak bone density in “standard deviations” (SD).
Auckland Bone Density specialists use the T-score to diagnose osteoporosis.
The World Health Organisation (WHO) has defined the T-scores and what they mean. If more than one bone is tested we use the lowest T-score to determine whether you have osteoporosis or not.
What your T-score means:
World Health Organization Definitions of Osteoporosis Based on Bone Density
1.0 0.5 0 -0.5 -1.0
-1 and above
Between -1 and -2.5
Low BMD (Osteopenia)
-2.5 -3.0 -3.5 -4.0
-2.5 and below
A T-score between +1.0 and -1.0 is normal bone density, e.g., +0.7, +0.1, -0.3, -0.8.
A T-score between -1.0 and -2.5 indicates low bone density or osteopaenia, but not osteoporosis, e.g., could be -1.3, -1.8, -2.2.
A T-score of -2.5 or lower establishes the diagnosis of osteoporosis, e.g., could be T-scores of -2.8 and -3.5.
The lower the T-score the lower your bone density is, i.e., a T-score of -0.5 is lower than a T-score of +0.5 and a T-score of -3.5 is lower than a T-score of -3.0. For DXA testing, 1 SD difference in a T-score equals a 10-15% decrease in bone density, e.g., a person with a T-score of -3.0 has a 10-15% lower BMD than a person with a T-score of -2.0.
DXA BMD testing also includes a Z-score which compares your bone density to that in someone else of your age, similar body size and similar ethnicity. Auckland Bone Density does not use Z-scores to diagnose osteoporosis in adults over the age of 50 years, but these are used by our experts in recommending whether further investigations are needed for unusual causes of osteoporosis. The Z-score is used by our experts in reaching conclusions and recommendations in children and adults under the age of 50 years. However, routine BMD testing is not recommended in these age groups.
When to Consider Treatment
The results of the BMD test help our specialists and your own doctor reach conclusions and recommendations about prevention or treatment of osteoporosis. These recommendations are made in the knowledge of your other risk factors, your medical history and current health and medications and your likelihood of having future fractures.
Below are our treatment guidelines for postmenopausal women and men aged 50 or older.
Most people with T-scores of -1.0 and above (normal bone density) do not need any form of prevention or treatment.
People with T-scores between -1.0 and -2.5 (osteopaenia) only require osteoporosis medications when certain risk factors are present.
People with T-scores of -2.5 and below (osteoporosis) should consider taking an osteoporosis medication.
Absolute Fracture Risk
In 2008, the WHO released a set of calculators which can be used to determine the estimated risk of an individual experiencing a bone fracture over the next 10 years. Postmenopausal women and older men with osteoporosis are at the greatest risk of breaking bones. These calculators have enabled greater certainty about when the treatment for osteopaenia or osteoporosis becomes wise, since many factors are taken into account in reaching a conclusion as to the true likelihood of experiencing fractures. Our Specialists at Auckland Bone Density use this new tool in calculating your personal fracture risk. In some circumstances, an alternative calculation tool, the Garvan calculator, is used.
These medications have been proven to slow or stop bone loss and in many instances to rebuild lost bone. They have also been shown to reduce the chances of breaking bones by up to 50%. Our Specialists and your own doctor will consider both the risks and benefits of taking medication and will include consideration of potential side effects.
Osteoporosis medications are enhanced by adequate calcium and vitamin D. Weight bearing exercise may further enhance the benefits. Our Bone Specialists at Auckland Bone Density recommend a healthy food intake of calcium (800-1000mg) and a minimum of 800IU of vitamin D daily. The vitamin D supplement mostly available in New Zealand is cholecalciferol and this can most readily be taken as a single tablet of 1.25mg cholecalciferol ("calciferol") each month (50,000 units IU). However, many people gain adequate vitamin D from their sunlight exposure.
All medications registered in NZ are listed in detail with the government agency Medsafe. www.medsafe.govt.nz