Many people who want to know the status of their bone health don't want to undergo a DEXA test (bone density scan) for a number of reasons. One is the expense, but even more significant is that the DEXA test creates exposure to ionizing radiation. Even though it's reported to be a low dose, more and more people are becoming uncomfortable with being exposed to any more radiation than they absolutely have to be, especially after the Japan nuclear site leaks, which are spreading radiation across the planet on the prevailing winds.
And then, there's the uncertainty about what the DEXA scan results actually mean and whether or not the test results are accurate and therefore can be relied upon. Questions about accuracy is a pertinent concern, because if the test is conducted on a different machine than was used previously, scores can be higher or lower. Therefore the reading results are not directly reflecting the actual density of bones, but rather also include influences from equipment that measured them.
Then, there's the T score Z score issue. Many people question the validity of comparing an older woman's bone density score to the average bone density of a 35 year old woman, which is what the T score evaluates. Better, they say, to use the Z score, which compares bone density of the patient with that of others her own age. After all, you wouldn't expect to compare the vision of a 65 year old with that of a 35 year old - some decline is expected with age and is not in that case cause for aggressive treatment with medications.
These and other reasons are why many people want a different test. Do such things exist?
The short answer is, 'yes', some other tests do exist. That said, it's important to know that these other tests are going to give a different answer than a DEXA answers because each of these tests asks a different question.
A question answered by DEXA scan results is "how dense are my bones?" A DEXA scan result, when compared to a previous one on the same equipment, can also address, "Does it appear that I have gained or lost bone since my last scan?"
Two alternative tests answer different but relevant questions, which are:
"Does it appear that I am I breaking down bone right now, and
"If so, how much?"
To answer that question, by-products of bone breakdown can be measured in the urine. These tests have several advantages:
1. They have the possibility of uncovering a bone loss process in its earlier stages;
2. They carry no risk of exposure to x-rays or photons; and
3. They are far less expensive than DPA or DEXA.
Before interpreting the results, however, you should know that measurements can vary by up to 40 or even 50% from one day to the next - not because the tests are inaccurate, but because bone loss rates can vary that much from day to day, and even hour to hour!
One such test measures the level of calcium excretion in the urine. However, if the test shows a higher rate of calcium excretion, that still doesn't mean the calcium is being taken from the bone. For example, the body could be dumping calcium due to high protein intake where the body is attempting to get rid of some calcium to balance phosphorus ratios, and the high score has nothing to do with bone loss at all.
Also, a great deal depends on when in the course of the bone breakdown process the tests are taken: urinary calcium is increased in the initial phases of bone depletion, normal later, and low when the bone bank calcium deposits are drained.
Another urine test measures pryidinium crosslinks, which are metabolic products that show up in the urine when bone type I collagen is being broken down. Again, this is a test that takes a 'snapshot' of the bone loss process at the moment the test is taken.
Normal laboratory values for these test people are still being determined to discover normal levels for people of different ages.
Therefore, interpreting these results remains a matter of opinion.
Still, for a variety of reasons, such alternative test results can be valuable in attempting to discover status of the mineral density of your bones - and doing so without a radiation dose!
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