Follow-up Bone Density Tests
Since changes to bone happen relatively slowly, depending on your initial test results, you may not need another DXA for at least two years. On the other hand, if your health care provider is concerned that you may be losing bone quickly or is putting you on a treatment that acts quickly, you may need to get retested sooner. If you are getting re-tested within two years of your last test, be sure to check with your insurance company about coverage.
For you and your health care provider to follow potentially small changes in bone density is difficult. The best thing you can do is return to the same DXA machine where you were originally tested. Going back to the same machine increases the likelihood that your previous images are on the machine and that the technician can create a better replication of your previous test. If returning to the previous machine is not possible, always keep your test results or ask your health care provider for the images. Bring the images with you when you are retested. This will help the technician position you and measure the same location as your previous DXA.
Even when you return to the same machine and the same technician, there is bound to be slight variations in the repeat testing. We call this “least significant change.” At good DXA centers, the technicians test their ability to replicate the positioning of patients. To do this, they get patients to volunteer to be scanned, then get up off of the table and then be scanned again. Least significant change will vary from DXA center to DXA center, but can run from about 3% to 5%. What this means for you is that an increase or decrease in bone density must exceed the least significant change at the DXA center. For example, if your results indicate that your bone density decreased by 3% since your last scan, and the least significant change for the DXA center is 4.3%, the physician reading your report would not say that you had lost bone density. You would need to lose more than 4.3% of your bone mass for it to be considered a significant loss.