How to Understand Your Results
What Do BMD Test Results Mean?
The following information should help you understand what your BMD test results mean but you should always discuss your results with your healthcare provider.
Your first BMD test tells you the density of your bones at that specific time. However, it can not tell you if you have lost bone or are losing bone. The only way to diagnose bone loss is to have a repeat BMD test, usually two years later. Your healthcare provider can determine if you are losing bone by comparing the initial and repeat BMD test results.
There are two scores used 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.
What is normal bone mass and how is it diagnosed?
Normal bone mass is when your bone density, or bone thickness, is within the normal range of the average bone density of young healthy adults of your same gender Normal bone mass is diagnosed when your T-score is -1.0 and above, for example, -1.0, 0, +1.0, and above.
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 –1.0 and –2.5. If you have been diagnosed with low bone mass, it is important to speak to your healthcare provider about your results and take action to promote strong 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 BMD test can diagnose osteoporosis when your T-score is –2.5 or below, for example -2.5, -2.6,…-3.0….-3.5 and below. The lower your bone mass, the greater your risk for fracture. Osteoporosis can also be diagnosed if you have a history of a broken bone in your hip or spine without major trauma (such as a motor vehicle accident or a fall from a high surface).
What if I have low bone mass or osteoporosis?
If your BMD test results indicate that you have osteoporosis, your healthcare provider may prescribe a medication for osteoporosis treatment. If you have low bone mass along with strong risk factors for osteoporosis and/or fracture, your healthcare provider may prescribe a medication to prevent further bone loss and reduce the risk for fractures. After an osteoporosis medication is prescribed 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.
What is a Z-score and what does it mean?
The T-score, as discussed above, is used to diagnose normal bone mass, low bone mass, or osteoporosis. Sometimes healthcare providers get important information about your bone health by evaluating another result of the BMD test called the Z-score. The Z-score is used to compare your bone density to the average values for a person of your same age and gender. For example, if you are a 65 year old woman, a Z-score compares your bone density to that of other 65 year old women. 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 healthcare provider may recommend additional tests to better understand why your bone mass is so low or she/he may refer you to an osteoporosis specialist.
Will a BMD test alone tell me my risk for breaking a bone?
Your BMD is one of the best predictors of your risk for breaking a bone. In addition to your BMD results, your healthcare provider will also consider several other factors. There is a computer program (FRAX) that can be used by your healthcare provider to help determine your risk for fracture in the next ten years if you meet the following criteria:
- you have low bone density
- you are a postmenopausal woman or a man age 50 or older, and
- you are not currently taking osteoporosis medications or have not taken osteoporosis medications in a 1 to 2 year period of time (depending on the medication)
The risk factors used in FRAX include:
- Personal history of fracture (you are more likely to break a bone if you have already broken one)
- Family history of hip fracture (if your parent broke their hip, you are at greater risk for a hip fracture)
- Low body weight for height
- Current cigarette smoking
- Diagnosis with certain diseases or use of certain medications
In some cases, your healthcare provider may recommend additional tests to better understand your fracture risk. Research is helping us to better understand other risk factors for fracture.