All About Bone Mineral Density Tests
Osteoporosis is a silent disease.
You cannot see or feel your bones getting thinner. Many people do not even know that they have thin bones until a bone breaks (fractures). A broken bone can interfere with your daily activities and can have serious consequences. It is important for you to know whether you have this silent disease so you can take steps to prevent a fracture and protect your ability to lead an independent, active lifestyle.
What is a Bone Mineral Density (BMD) test?
A bone mineral density test is an easy reliable test that measures the density, or thickness, of your bones. It measures the amount of mineral (calcium) in a specific area of bone. The more mineral you have in the bone measured, the greater your bone density or bone mass.
A BMD test can:
- Measure the density of your bones
- Detect osteoporosis before a fracture occurs
- Help to predict your chances of fracturing in the future
- Monitor the effectiveness of treatments for osteoporosis
What is it like to have a BMD test and is it safe?
The most standardized method to measure bone density is called dual x-ray absorptiometry (DXA) of the hip and spine. It is a quick and easy test. It is not necessary to undress as long as you have no buttons, zippers or snaps on your clothing from your chest to thigh. You simply lie on a table while a fast, painless low-dose x-ray is taken. Nothing is injected or swallowed. The radiation is so low that no protective shields are necessary for the patient or the x-ray technologist. In fact, the radiation approximates the background radiation you receive flying in an airplane from New York to California. That is only 10% of the radiation exposure of a chest x-ray.
Who should have a BMD test?
Don’t let osteoporosis sneak up on you; find out if a BMD test is appropriate for you. The first and most important step is to assess your personal risk for osteoporosis. For more information about how to determine your risk factors, see the appropriate NYSOPEP risk assessment tool: Osteoporosis Risk Assessment for Postmenopausal Women, Premenopausal Women or Men.
In general, bone mineral density testing is recommended for the following individuals:
- All women aged 65 or older regardless of risk factors;
- Postmenopausal women under age 65 who have one or more risk factors (other than race, gender and postmenopausal status);
- Postmenopausal women who have a current and/or previous fracture with minimal trauma;
- Adults (including postmenopausal women, premenopausal women and men) on steroid medications for more than three months; and
- Men with a current/ previous fracture or a major risk factor for osteoporosis such as low testosterone, alcoholism, or any other secondary cause of osteoporosis.
The decision to have a BMD test should be made in collaboration with your medical professioanal. If a bone density test is recommended for you, you will need a prescription from your medical professional.
Will my insurance company pay for a BMD test?
Private insurance companies, HMOs, Medicare and Medicaid may cover part of the cost of a bone density test. Coverage varies depending on your age, gender, and medical history. Different insurance companies use different guidelines for reimbursement criteria. Contact your insurance carrier to find out about your specific coverage for a BMD test.
What do my BMD test results mean?
At first, you may find it difficult to understand your bone density test results. The following information should help you understand what your test results mean. Of course, it is always necessary to discuss the meaning of your results with your medical professional.
Your first bone density test tells you the current density of your bones at that specific time. However, it can not tell you if you have lost bone or are currently losing bone. The only way to diagnose bone loss is to have a repeat bone density test, usually two years later. Your medical professional can determine whether you are losing bone by comparing the initial and repeat bone density test results.
There are two scores used by experts to interpret bone density test results, the T-score and the Z-score.
What is a T-score and what does it mean?
The World Health Organization (WHO) uses T-scores to define normal bone mass, low bone mass (or osteopenia), and osteoporosis. The T-score compares your bone density to the average bone density of young healthy adults of your same gender . By using the diagram below, you can see how T-scores are used to define the status of your bone health.
| Using T-Scores to Define Bone Health | |||
|---|---|---|---|
| DIAGNOSIS BASED ON BONE DENSITY TEST GRAPHIC | |||
 |
|||
| Osteoporosis | Low Bone Mass | Normal Bone Mass | High Normal Bone Mass |
| ...-4.0 through -2.5 | -2.5 through -1.0 | -1.0 through +1.0 | +1.0 through +4.0... |
| *T-scores are based on statistical measurements called standard deviations (SD) that reflect the differenece between one's bone density and normal bone density in the reference population. | |||
What is a Z-score and what does it mean?
A Z-score compares your bone density to the average values for a person of your same age and gender. A low Z-score (below —2.0) is a warning sign that you have less bone mass (and/or may be losing bone more rapidly) than expected for someone your age. If your Z-score is low, your medical professional may recommend additional tests to better understand why your bone mass is so low or she/he may refer you to an osteoporosis specialist.
What is low bone mass and how is it diagnosed?
Low bone mass, often called osteopenia, is not a disease but a condition in which your bone density, or bone thickness, is lower than the average bone density of young healthy adults of your same gender. Low bone mass is diagnosed when your T-score is between —1 and —2.5. If you have been diagnosed with low bone mass, it is important to speak to your medical professional about your results and take action to promote healthy bones. See "Promoting Healthy Bones".
What is osteoporosis and how is It diagnosed?
Osteoporosis is a disease that causes bones to become thin and weak, often resulting in fractures (broken bones) A bone density test can diagnose osteoporosis when your T-score is —2.5 or below. The lower your bone mass, the greater your risk for fracture. Osteoporosis can also be diagnosed if you have a history of fractures without trauma. See "The Facts about Osteoporosis"
What if I have low bone mass or osteoporosis?
If your bone density test results indicate that you have osteoporosis, your doctor may prescribe a medication for osteoporosis treatment. If you have low bone mass along with strong risk factors for osteoporosis and/or fracture, your doctor may decide to prescribe a medication for osteoporosis prevention. After a medication is chosen for you, repeat BMD tests may be used to monitor how your bones have responded to the treatment. It is ideal to have follow-up BMD tests performed on the same machine, at the same location, as your first bone density test. However, if you are not able to return to the same location, select a center that has the same model of DXA machine. This is necessary in order to make accurate comparisons and to be able to monitor the effectiveness of treatments for osteoporosis.
Are there different types of BMD tests?
Although there are a variety of different techniques to measure bone mineral density. Dual x-ray absorptiometry (DXA) of the hip and spine is the most reliable, fastest and most accurate. Some of the other methods to measure bone mineral density include quantitative computer tomography of the spine (QCT) or forearm (pQCT), radiographic absorptiometry (RA) of the middle finger, single x-ray absorptiometry (SXA), peripheral DXA (pDXA) of the forearm or heel, and ultrasound (QUS) of the heel or shinbone.
How is a "Bone Scan" different from a Bone Mineral Density (BMD) test?
The term "bone scan" is often used incorrectly to describe a bone mineral density test. Unlike a BMD test, a bone scan is an invasive test. The patient is injected with a dye that allows a scanner to look at the condition of bone tissue. A bone scan can diagnose inflammation, fractures, bone lesions and cancer. However, in the absence of fractures, it cannot predict the risk of osteoporosis or diagnose the condition.
Will a BMD test alone tell me my risk for breaking a bone?
In addition to a BMD test, there are many factors that play an important role in determining your bone strength. If your bone strength is low, you may be at greater risk for breaking a bone. The BMD test measures bone quantity (the amount of bone you have). It will tell you if you have a low amount of bone (or low bone mass). Low bone mass is one of the best predictors of fracture risk. In addition to your bone density test results, your medical professional will also consider several other factors in order to define your risk for fracture. For example, the risk for fracture increases as you age. There are also risk factors for hip fracture that are independent of your BMD test results. The risk factors for hip fracture include a personal history of fracture (you are more likely to break a bone if you have already broken one); family history of maternal hip fracture (if your mother broke her hip, you are at greater risk for a hip fracture); low body weight (women weighing less than 127 pounds); fraillty; a tendency to fall frequently; and current cigarette smoking. In some cases, your medical professional may recommend additional tests to better understand your fracture risk. Research is helping us to better understand other risk factors for fracture that cannot easily be measured such as bone quality.
(c) Helen Hayes Hospital/NYS Department of Health - 11/03
