Nearly every day I see women and physicians themselves getting very worried when a woman’s bone density tests show even a small 1-2% decline. Women are often told their fracture risk has greatly increased and that they should immediately begin osteoporosis drug therapy. For many women, the growing “osteoporosis fear” is fueled by small reductions in bone density. But what do these small changes really mean, and just how accurate are the DEXA bone density tests anyway?
Thanks to the excellent work of the University of Washington osteoporosis specialist, Dr. Susan Ott, we now know that the common bone density test is rather imprecise and large changes in density are needed to assure that bone loss is indeed occurring, much less significant in nature. A thoughtful scientist, Dr. Ott had 300 patients get two bone density measurements: one when they came into the room, and the second after walking around the room for a while. With this simple experiment she showed that repeat measurements on the same day may show as much as 7% difference in bone mineral density. Breaking down the data she found that while a 4-6% change in bone mineral density indicates a “probably change” it takes more than a 6% change to fully guarantee a statistically significant change in bone density.
The Better Bones perspective on bone density testing: Bone density testing can be useful, especially when spaced over many years, but small changes are not significant and certainly not a basis for beginning bone drug therapy.
Dr. Susan Ott’s website: http://courses.washington.edu/bonephys/opBMDp.html