Z-score
Also called: Z score
What it means
A Z-score compares your bone density to other people your own age and sex, which matters most for younger adults, men under 50, and children.
Knowing which score applies to you helps you and your doctor read your bone scan correctly, instead of relying on a number meant for a different age group.
A Z-score compares your bone density to other people your own age and sex, instead of comparing you to a healthy 30-year-old (which is what a T-score does). This distinction matters most for certain groups: anyone premenopausal, men under 50, and children. For these groups, the Z-score is considered the right number to focus on, because a T-score can be misleading at that age.
Your bone density report usually lists results at the lumbar spine, femoral neck, and total hip, and these numbers can disagree with each other. That's because the spine is mostly trabecular bone, which turns over quickly, while the hip has more cortical bone. Diagnosis is typically based on whichever valid site gives the lowest score. Things like spinal arthritis, calcium deposits in the aorta, or old compression fractures can also add extra mineral in the scan's path and make the spine reading look falsely better than it is - part of why a careful report pays attention to the hip as well.
When you're building a record of your bone health, it helps to write down both your T-score and Z-score at each site, along with the date and facility of the scan. Because bone health is best understood as a trend over time rather than one single result, having this information together, and asking your physician about your actual fracture risk and which site is being tracked, gives you a clearer picture than the score alone.
How sure is this?
Graded Established Science: Supported by broad scientific consensus and decades of research. Read each study with its grade in mind. One study is a piece of the picture, not the whole of it.
Where the Academy teaches it
This page is the short version. The lessons teach it in full, with the context around it and a quiz to lock it in.
Questions people ask about this
A T-score compares your bone density to that of a healthy young adult, measured in standard deviations: -1.0 and above is normal, -1.0 to -2.5 is osteopenia, and -2.5 or below is osteoporosis. But it's just one snapshot of density — it doesn't capture bone quality, your fall risk, or your overall fracture probability, so it's worth tracking several other things alongside it and discussing them with your physician.
Read the full answer →Osteopenia and osteoporosis are both based on your DEXA T-score, just at different points on the same scale. A T-score between -1.0 and -2.5 is called osteopenia (lower-than-average bone mineral density), while -2.5 or below is called osteoporosis (more significant bone loss). They're not two different diseases — they're a continuum, and the cut-off points are statistical conventions used for research and reimbursement, not a biological cliff where something suddenly changes in your skeleton.
Read the full answer →For most people, the honest answer is every 1 to 2 years. DEXA machines have a built-in measurement error, and most facilities can't reliably detect a real change in bone density sooner than that — a small shift of 1-2% on your scan often just reflects machine noise, not actual bone loss or gain. Your physician can tell you the right interval for your specific situation.
Read the full answer →A T-score compares your bone density to that of a healthy young adult at peak bone mass, and it's the number used to apply the standard categories of normal, osteopenia, or osteoporosis. A Z-score instead compares you to people of your own age and sex, which makes it the more appropriate number for anyone premenopausal, for men under 50, and for children, since a T-score can be misleading in those groups.
Read the full answer →Related words
A T-score shows how your bone density compares to a healthy young adult, measured in standard deviations, and it's…
A DEXA scan is a low-radiation X-ray test that measures how much mineral is in your hip and spine bones, giving you…
Bone mineral density (BMD) measures how much mineral is packed into your bones, usually estimated with a DEXA scan,…
Trabecular bone is the spongy, honeycomb-like bone found inside structures like your spine and hip, providing…
Cortical bone is the dense, hard outer layer of bone that forms a protective shell and resists bending and twisting…
Education only, not medical advice. Decisions about tests, medications and treatment belong with your own doctor. OsteoStrong does not diagnose, treat or cure any disease.
