Where did my bones go?

I am often referred patients because the follow-up dual energy X-ray absorptiometry scan reported bone loss, even when patients are on appropriate therapy.

Unfortunately, much of the time, this is an artifact resulting from poor reproducibility from one DEXA study to the next, or the two DEXA studies have been done on different instruments.

Let’s tackle the second issue first. The DEXA technology is not identical on machines made by different manufacturers and there are even differences between different models from the same manufacturer. The only sure way to get around these problems is to make sure that the patient goes back to the same DEXA testing center for each serial study. Not always easy because insurers may have changed their preferred sites without knowledge of the technical problem this causes. It’s worth being insistent because it will save them all the expenses of trying to find out why the bone density went down.

Even when the patient does have the follow-up study done at the same facility, differences between the two studies can creep in. It requires skill to position a patient in exactly the same way 12 or 24 months apart. If you only receive a brief summary report you cannot tell if the decrease in bone density is real or not. Before embarking on a search for what might be wrong, take time to have the testing facility carefully review the more complete data for reproducibility. A full DEXA report contains several pages of primary data about the area scanned. A good lab will do this routinely but not all labs take the time to check this.

Think about a patient or two where this unexpected “bone loss” has happened and try and get a copy of the primary data to check for yourself. Drop me a note if you want more help with this issue.

Next time I will review some of the circumstances that might result in true bone loss.