A DEXA scan reports bone strength as a T-score, the number of standard deviations between your density and that of a healthy thirty year old at peak bone mass. Zero is perfect parity, minus one is the normal floor, minus two point five marks osteoporosis. Enter the scanner’s BMD value plus the reference mean and deviation from your report to compute and classify the score.
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Scientific references
Bone density machines could report raw grams per square centimeter, but raw numbers mean nothing without context, since machines and skeletal sites differ. The T-score solves this by expressing your result in standard deviations from peak young adult bone mass, creating a universal language every guideline speaks.
The WHO Bands
The World Health Organization defined the categories that still govern diagnosis. A T-score of minus one or better is normal. Between minus one and minus two point five lies osteopenia, low bone mass, a warning zone rather than a disease. At minus two point five and below the diagnosis is osteoporosis, and adding an existing fragility fracture makes it severe or established regardless of score.
Every Point Doubles the Risk
The T-score’s power is its risk gradient. Fracture risk roughly doubles for each standard deviation below peak mass, so a woman at minus two carries about four times the hip fracture risk of one at zero. This exponential shape is why small further losses in the osteopenic range matter more than the absolute number suggests.
T Versus Z
Reports often show a Z-score too, which compares you against your own age group instead of young adults. A poor T with a normal Z simply reflects normal aging, while a poor Z, below minus two, prompts a search for secondary causes like steroid use, celiac disease or hormonal disorders.
Treatment decisions never rest on the score alone. Fracture history, falls risk and tools like FRAX that fold in clinical factors decide who benefits from medication beyond calcium, vitamin D and weight bearing exercise.