A T-score is a number from a bone density test that tells you how your bones compare to those of a healthy young adult. It’s measured in standard deviations, which is a statistical way of expressing how far above or below average your result falls. A T-score of 0 means your bone density matches the average for a healthy 25- to 35-year-old of your same sex and ethnicity. A negative number means your bones are thinner than that benchmark.
How the Score Is Calculated
During a bone density test (called a DXA scan), a low-dose X-ray measures how much mineral is packed into your bones, typically at the hip and spine. That measurement is then compared to the average bone density of healthy young adults in their peak bone years, roughly ages 25 to 35. The gap between your result and that reference average, expressed in standard deviations, is your T-score.
If your bones are denser than average, you’ll get a positive number. If they’re thinner, you’ll get a negative number. The further below zero, the greater the bone loss. A T-score of -1.0, for example, means your bone density is one standard deviation below the young-adult average. A score of -3.0 means it’s three standard deviations below.
What the Ranges Mean
The World Health Organization established diagnostic categories in 1994 that are still used today:
- Normal: T-score of -1.0 or above
- Osteopenia (low bone mass): T-score between -1.0 and -2.5
- Osteoporosis: T-score of -2.5 or below
Osteopenia isn’t a disease on its own. It’s a middle zone that signals your bones are weaker than ideal but haven’t crossed the threshold into osteoporosis. Many people with osteopenia never fracture a bone, but the category flags you for closer monitoring and lifestyle changes like weight-bearing exercise and adequate calcium and vitamin D intake.
Osteoporosis means your bones have thinned enough that fracture risk is significantly elevated. At this level, bones can break from relatively minor falls or, in severe cases, from everyday movements like bending or coughing.
How T-Scores Relate to Fracture Risk
The relationship between T-scores and fracture risk is straightforward: for every one standard deviation drop below the young-adult average, your risk of fracture roughly doubles. So someone with a T-score of -2.0 has approximately twice the fracture risk of someone at -1.0, and about four times the risk of someone at 0.
That said, bone density alone doesn’t capture the full picture. Factors like age, body weight, smoking history, family history of fractures, and whether you’ve already broken a bone all influence how likely a fracture is. Clinicians often use a tool called FRAX, which combines your T-score with these personal risk factors to estimate your 10-year probability of a major fracture. This helps determine whether medication makes sense or whether lifestyle changes alone are sufficient.
When Treatment Is Recommended
A T-score of -2.5 or lower at the hip or spine is the most common threshold for starting osteoporosis medication. But treatment decisions aren’t based on a single number. The Bone Health and Osteoporosis Foundation recommends considering medication for people with osteopenia (scores between -1.0 and -2.5) if their FRAX results show a 10-year probability of 20% or higher for a major osteoporotic fracture, or 3% or higher for a hip fracture specifically.
For people in the osteopenia range with lower fracture risk, the typical approach involves weight-bearing and resistance exercise, ensuring adequate calcium and vitamin D, quitting smoking, and limiting alcohol. A follow-up DXA scan every one to two years can track whether bone density is stable, improving, or declining.
T-Score vs. Z-Score
Your DXA report may also include a Z-score, which compares your bone density to the average for people your own age, sex, and body size rather than to a young-adult reference. Z-scores are more useful for younger adults, premenopausal women, and children, because comparing a 30-year-old’s bones to a 30-year-old reference population is more meaningful than comparing them to a peak-bone-density standard they haven’t yet departed from. For postmenopausal women and men over 50, the T-score is the standard diagnostic measure.
Who Should Get a Bone Density Test
The U.S. Preventive Services Task Force recommends routine bone density screening for all women aged 65 and older. Postmenopausal women younger than 65 should be screened if they have one or more risk factors for osteoporosis, such as low body weight, a parent who fractured a hip, smoking, or long-term use of medications that weaken bone (like corticosteroids). These recommendations apply to adults 40 and older who haven’t already been diagnosed with osteoporosis or experienced a fragility fracture.
For men, there’s no universal screening recommendation yet. Evidence on the benefits and harms of routine screening in men is still considered insufficient by the task force, though individual doctors may recommend testing for men with clear risk factors like long-term steroid use, low testosterone, or a history of fractures.
What to Expect From the Test
A DXA scan is painless and takes about 10 to 15 minutes. You lie on a padded table while a scanner passes over your body, typically focusing on the lower spine and one or both hips. There’s no injection, no fasting, and no recovery time. The radiation exposure is extremely low, a small fraction of what you’d receive from a standard chest X-ray.
Your results will list T-scores for each site scanned. If one site shows a score of -1.8 and another shows -2.6, the lower score is what determines your diagnosis. In this example, you’d be classified as having osteoporosis based on the -2.6 reading, even though the other site falls in the osteopenia range.