Jun 7, 2012 09:16PM otter wrote:
cookiegal, one thing I would wonder is, how much variation might there be in results from one DEXA scan to another even if there was no change in bone density? What would happen if someone had two DEXA scans on the same day? How similar (or dissimilar) would those results be?
I've been told there can be a lot of variation from one scan to another depending on the machine and the technician doing the scan. I know for a fact that there can be a lot of variation based on exactly how you have your leg(s) positioned. I was going to an endocrinologist 10 years ago, and he ordered a DEXA scan even though I wasn't menopausal yet. My bone density was wonderful -- way up in the "green" zone, well above the osteopenia line. Two years later, he insisted on another DEXA scan, this time to "prove" to me that I was losing bone because I had declined his recommendation of estrogen/progesterone replacement therapy (HRT).
To his amazement, my bone density had increased during those two years, even though I was clearly perimenopausal by then. What he didn't know was that his new DEXA tech had no clue how to position someone's leg and hip for a DEXA scan -- the guy just told me to lie on my back and hold still. He didn't use one of those triangular pillows or anything to hold my leg and hip in the proper position. As a result, my leg was splayed out too far and one of the big, bony bumps on the side of the femur ended up being scanned and adding to the total amount of bone. It's hard to explain without using anatomical terms; but what happened was a common mistake rookie/untrained DEXA techs make. The result is an inaccurate DEXA result. I didn't tell the endocrinologist about the mistake, because it was his tech who screwed up (the scans were done in-house) and the endocrinologist was a jerk anyway.
This is a long story with a short conclusion: IMHO, and from what my med onco and new endocrinologist have said, DEXA scans are not very accurate. It's difficult to tell whether a change is the result of a real difference in bone density or is because of variation in the conduct of the test or interpretation of the results.