Understanding Your T-Score: What Your Bone Scan Results Actually Mean

You have had your DEXA scan, and now you are staring at a printout with numbers, scores, and statistical comparisons that look more like a maths exam than a medical result. You see a T-score of -1.8 and wonder: is that bad? What does -2.5 mean? And what on earth is a Z-score? Understanding what your bone scan results actually mean — in plain English — is essential for making informed decisions about your bone health. This guide breaks it all down.

What Is a T-Score?

A T-score is a number generated by your DEXA scan that compares your bone mineral density to the average peak bone density of a healthy young adult of the same sex. In other words, it tells you how your bones stack up against a person at their strongest, usually around age 30.

A T-score of 0 means your bone density exactly matches the young adult average. Positive T-scores indicate above-average bone density (strong bones), while negative T-scores indicate below-average density. The more negative the number, the lower the bone density and the higher the fracture risk.

The Three T-Score Categories

The World Health Organisation defines three categories based on T-score. Normal bone density is a T-score of -1.0 or above. This is a healthy range — your bones have sufficient density to withstand normal stresses. Osteopenia is a T-score between -1.0 and -2.5. This indicates low bone mass — not yet at osteoporosis levels, but lower than ideal. It is a signal to pay close attention to bone health. Osteoporosis is a T-score of -2.5 or below. At this level, bones have lost enough density that fracture risk is significantly elevated.

A separate category — severe osteoporosis — applies when the T-score is -2.5 or below and one or more fragility fractures have already occurred.

What Is a Z-Score?

Your DEXA report may also include a Z-score. Unlike the T-score, which compares your density to a young adult reference, the Z-score compares your bone density to the average for someone of your own age and sex. A Z-score tells your doctor whether your bone density is appropriate for your age group.

A Z-score significantly below -2.0 suggests your bone loss is greater than expected for your age, which may point to a secondary cause — a medical condition, medication side effect, or nutritional deficiency — rather than age-related bone loss alone. In premenopausal women and men under 50, the Z-score is actually more useful than the T-score for guiding decisions.

T-Score by Site: Spine vs. Hip

Your DEXA scan will produce separate T-scores for different skeletal sites — typically the lumbar spine (vertebrae L1 to L4) and the hip (which includes the femoral neck and total hip). These scores can differ, sometimes quite significantly. This is normal. Bone density is not uniform throughout the body. Your clinical diagnosis and fracture risk are generally based on the lowest T-score across the measured sites.

Be aware that spine T-scores can occasionally be artificially elevated by conditions like arthritis, calcified arteries, or previous spinal fractures, which makes the hip T-score particularly important in older adults.

T-Score Alone Is Not the Full Picture

Here is something very important to understand: your T-score is a crucial piece of information, but it does not tell the full story on its own. Fracture risk is influenced by many factors beyond bone density, including age, sex, prior fractures, family history of hip fracture, smoking, steroid use, and falls risk. A 75-year-old with a T-score of -2.0 has a significantly higher fracture risk than a 50-year-old with the same score, even though both are in the osteopenia range.

This is why doctors use the FRAX tool — a clinically validated online calculator developed by the University of Sheffield — to combine T-score with other risk factors and produce a 10-year probability of major osteoporotic fracture and hip fracture. The FRAX result is often more useful for treatment decision-making than T-score alone.

What Happens Next?

If your T-score is normal, your doctor will likely recommend repeat testing in three to five years and standard bone health maintenance through diet and exercise. If your T-score shows osteopenia, you will probably discuss lifestyle optimisation, possible supplementation, and the timeline for follow-up testing. If your T-score shows osteoporosis, you will have a fuller conversation about fracture risk, lifestyle changes, and whether medication is appropriate.

Whatever your results, the most important step is to have a clear conversation with your doctor about what they mean for your specific situation and what your next steps should be.

Frequently Asked Questions

My T-score got worse since my last scan — does that mean treatment isn't working? Not necessarily. A small change in T-score (within about 3–5%) may be within the margin of measurement error. What matters more is the trend over multiple scans. Discuss any changes with your doctor rather than drawing conclusions from a single comparison.

Can a T-score improve? Yes. With appropriate treatment, lifestyle changes, and supplementation, many people see modest improvements in bone mineral density over time. The primary goal of treatment is to reduce fracture risk, and this can be achieved even without dramatic improvements in T-score.