The T-score is a comparison. It compares your bone density - measured in grams of mineral per square centimetre of bone - to the bone density of a healthy young adult woman at her peak. That peak typically occurs in the mid-thirties, when bone density is at its lifetime maximum. Your T-score tells you how far above or below that peak your bones currently sit.

Why the number is almost always negative

Peak bone mass is the reference point. So a T-score of zero means your bone density exactly matches a healthy young adult at her best. Almost no woman over 50 achieves that. A negative number simply means your bone density is below that peak, which is entirely expected as you age. The question is how far below.

A T-score of -1.0 means your bone density is one standard deviation below the young adult average. A T-score of -2.5 means it is two and a half standard deviations below.

The further the number falls below zero, the lower the bone density and the higher the fracture risk.

The three categories

The World Health Organization established three classifications based on T-score:

  • Above -1.0: Normal bone density
  • Between -1.0 and -2.5: Osteopenia - lower than ideal, but not yet osteoporosis
  • -2.5 or below: Osteoporosis

These are not arbitrary lines. Each threshold reflects a meaningfully different level of fracture risk, based on decades of research into how bone density relates to the likelihood of breaking a bone.

Why you have more than one T-score

Your report will show a T-score for each site that was scanned. This is typically the lumbar spine, the hip, and sometimes the forearm. Each site can show a different result, and that is completely normal. Bone density is not uniform across the body. Your spine might show osteoporosis while your hip shows osteopenia, or vice versa.

Your overall classification is determined by whichever site shows the lowest score.

What the T-score doesn't tell you

A T-score is a measure of density. It is not a measure of bone quality, bone structure, or fracture risk on its own. Two women can have the same T-score and very different fracture risks, depending on their age, history of previous fractures, family history, and other factors. This is why T-score alone is never the whole picture, and why fracture risk tools like FRAX exist to put the number in context.

What to do with your number

If your T-score is in the osteopenia or osteoporosis range, the most important thing is not to interpret it in isolation. Lenari's DEXA explainer reads your full report and puts your numbers in context. Your doctor can tell you what your T-score means specifically for your situation, your history, and your treatment options.

A number on a page is information. What matters is what you do with it.