What is bone density?
Bone mineral density (BMD) is a measure of the amount of calcified tissue inbones and is essentially an estimate of bone strength. 'Thin' bones are bones with less calcified tissue in a given volume of bone. Such bones remain the same size but contain less protein and less calcium, and are weaker and more likely to fracture.
What are the problems a low bone density can cause?
Reduced bone density increases the risk of fracture with minor accidents. Obviously, heavy falls or major accidents can lead to fracture in any individual regardless of bone strength, but those with reduced bone density are liable to fracture with minimal trauma. Osteoporosis is not, of itself, painful and is thus a 'silent' disorder until fracture occurs. Detection of osteoporosis by measurement of BMD is very helpful in order to assess fracture risk and to serve as a baseline to assess the response to treatment. A number of treatments can help restore bone density when this has been found to be low. It is important to maintain a good intake of calcium (eg as a supplement of 500-1000 mg per day) and, if elderly or out of the sun, a supplement of vitamin D (n using 1 or 2 multivitamin tablets per day).
How is my bone density measured?
BMD can be measured by a technique called Quantitative Computed Tomography (QCT). This involves the patient lying on a CT scanner couch for 5-10 minutes while the lower spine or hip is assessed. The technique is painless and very safe since x-ray exposure is very low compared to normal background radiation or a normal CT scan.
How are bone density results reported?
The QCT bone density value is reported as grams of bone per unit volume (e.g. 1.1g/ml), together with a statement of how this relates as a percentage to the bone density of the 'normal' population of the same sex, age, build and ethnicity.
When should bone density measurements be repeated?
Guidelines published by the Australasian Bone and Mineral Society discuss follow-up BMD measurements. In those with low bone density needing treatment it is suggested to repeat the measurement after 1-2 years to ensure the treatment is working and BMD is rising, in those with mild loss of BMD the measurement can be repeated after 3-5 years to see if there has been any further reduction, in which case treatment may be needed. Those with bone density at or above average levels should normally have a repeat measurement done at a longer intervals (perhaps 10 years) to ensure there is no bone loss over time.
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