So, you just had a follow-up bone density test, you’re frightened and disheartened. The doctor reports that since your last exam 3 years ago, your bone density test results show that you’ve lost 4% in your spine and 2% in your hip. The doctor says — forcefully — that you’re in danger of fracturing with this continued bone loss and recommended a bone drug for you to begin taking.

If you’re like most of my patients, your mind immediately goes in to self-critical mode: “Oh, no! What I’m doing isn’t working. I’m doomed to continue losing bone. I’ll end up fracturing just as the doctor suggests — perhaps even permanently handicapped!”

Nearly every day at the Center for Better Bones, I hear from people frightened by small changes in their bone density test. The problem is, they’re being needlessly frightened; in everyday clinical practice, one finds that these tests are not that accurate or reproducible.

So, take a deep breath, and let me explain another way to look at small changes in bone density measurements.

What bone density measurements really mean

The science of bone density testing leaves much to be desired. In the first place, the tests do not actually measure bone density; they simply estimate the mineral content of bone. And they can’t detect bone strength, which matters more than density. The assumption that bone density is the same as bone strength has long since been proven false: many, if not most, low trauma fractures — the hallmark of osteoporosis — do not have an “osteoporotic” bone density as defined by a T-score of –2.5. Also, today’s testing is very influenced by bone area — which means that lightweight and small-boned people come up with lower bone density readings than heavier folks with larger bones.

And then there is the fact that in everyday clinical practice the tests are not highly reproducible. You can put a person on the testing machine measure them, walk them around the room, then measure them again, only to find a significant difference between the two measurements — even using the same machine. Dr. Susan Ott, a well-known osteoporosis specialist, did just that — she placed 300 people on her machine, measured their bone mineral density, had them walk around the room, then did another bone density test. From her analysis, she found that we need to see a change of more than 6% to be certain of a statistically significant change in density.

Bone density test results: a cautionary tale

Consider Ken’s story. Ken is small-boned, lightweight, 56-year-old man who came to the Center for Better Bones seeking to improve his bone health. He had suffered several fractures in the past, but no new fractures in five years. No density tests have been done until recently, when his new doctor suggested they do one. Ken himself was curious about his bone density, and both Ken and his doctor were very taken aback when Ken’s bone density test results came back extremely low. They both felt it must be a testing error, so Ken underwent a second bone density test just 11 days after the first in the exact same medical facility.

Ken’s bone mineral density tests, done less than 2 weeks apart, showed a significant difference:
– The spine bone mineral density was 2% higher than on the first test.
– The neck of the hip bone density was 4.10% lower than on the first test.

It’s obvious that Ken isn’t losing bone in his hip while gaining bone in his spine, so clearly, the difference is built into the test’s error margin. This is not the first case where a medical test appears accurate and reproducible in highly controlled studies, but later is shown to be much less reproducible in real-life clinical practice.

And here’s the moral of the story: as far as bone density testing goes, “Don’t sweat the small stuff!”

Want to learn more about how to interpret your bone density test results? Take my e-course: How to Understand Your Bone Density Test & What It Means for You.

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