A DEXA scan report contains two key numbers: a T-score and a bone mineral density (BMD) value measured in grams per square centimeter. Your T-score is the number that matters most for understanding your bone health. It compares your bone density to that of a healthy young adult at peak bone strength, and it falls into one of three categories that determine whether your bones are healthy, thinning, or at risk for fractures.
What Your T-Score Means
The T-score is the centerpiece of your DEXA results. It’s a number that can be positive, zero, or negative, and it tells you how far your bone density falls from the ideal. Here’s how to read it:
- -1.0 or higher: Normal, healthy bone density.
- Between -1.0 and -2.5: Osteopenia, meaning your bones are thinner than normal but not yet in the osteoporosis range.
- -2.5 or lower: Osteoporosis, meaning significant bone loss that increases fracture risk.
Every single point your T-score drops increases your risk of breaking a bone by 1.5 to 2 times. So a person with a T-score of -3.0 has roughly double the fracture risk of someone at -2.0. The scale is continuous, not a simple pass/fail. A T-score of -2.4 (osteopenia) and -2.6 (osteoporosis) are only slightly different in actual bone strength, even though they fall in different diagnostic categories.
T-Score vs. Z-Score
Your report may include a second number called a Z-score. While the T-score compares you to a healthy young adult, the Z-score compares you to people your own age, sex, and ethnicity. Think of it this way: the T-score tells you how far you are from ideal bone density, while the Z-score tells you whether your bone loss is more than expected for someone like you.
Which score applies to you depends on your age and sex. If you’re a postmenopausal woman or a man 50 or older, your diagnosis is based on the T-score. If you’re a premenopausal woman, a man under 50, or a child, the Z-score is the relevant number. A Z-score of -2.0 or lower signals that your bone density is unusually low for your age group, which may point to an underlying cause like medication side effects or another medical condition.
Understanding the BMD Number
Alongside the T-score, your report lists a raw bone mineral density value in grams per square centimeter (g/cm²). This number represents how much mineral is packed into a given area of your bone. In healthy young adults, typical BMD values at the lumbar spine range from about 0.96 to 1.05 g/cm², and at the femoral neck (the narrow part of the hip bone) from about 0.80 to 0.85 g/cm².
The raw BMD number becomes especially important if you’re tracking changes over time. When comparing two scans, the change needs to exceed what’s called the least significant change (LSC), which is the smallest shift that counts as a real difference rather than normal measurement variation. For most people, that threshold is about 0.03 g/cm². If your BMD changed by less than that between scans, the difference could simply be measurement noise rather than actual bone loss or gain.
Why Different Sites Show Different Scores
A standard DEXA scan measures bone density at multiple locations, typically the lumbar spine (lower back), the total hip, and the femoral neck. It’s completely normal for these sites to show different T-scores. Your spine might read -1.8 while your hip reads -1.2, for example. Bone loss doesn’t happen evenly throughout the skeleton.
For diagnosis, the lowest T-score among the measured sites is generally the one that determines your classification. If any single site falls at -2.5 or below, that’s enough for an osteoporosis diagnosis regardless of what the other sites show. The femoral neck is often considered the most reliable single measurement for predicting hip fracture risk, which is the fracture type with the most serious health consequences.
One important caveat with spine measurements: arthritis, bone spurs, and compression fractures in the vertebrae can artificially inflate the BMD reading at the spine. If your spine score looks surprisingly good compared to your hip scores, especially as you get older, it may be worth discussing with your provider.
How Fracture Risk Is Calculated
Your T-score alone doesn’t capture your full fracture risk. A tool called FRAX combines your bone density with other factors (age, weight, smoking history, family history of fractures, and others) to estimate your 10-year probability of breaking a bone. In the United States, treatment is generally recommended when your 10-year risk of a major osteoporotic fracture reaches 20% or higher, or when your 10-year risk of a hip fracture specifically reaches 3% or higher.
This means someone with osteopenia and several other risk factors might need treatment, while someone whose T-score barely crosses into the osteoporosis range but has no other risk factors might take a more conservative approach. The T-score is the starting point, not the whole picture.
Body Composition Results
Some DEXA scans also measure body composition, breaking down your weight into fat mass, lean mass, and bone. If your report includes these numbers, two metrics are particularly useful to understand.
Visceral adipose tissue (VAT) measures the fat stored deep in your abdomen around your organs, which is the type most strongly linked to metabolic problems like diabetes and heart disease. Research from a large European study suggests that VAT levels above roughly 1,134 grams in women or 1,859 grams in men are associated with about a fourfold increase in the odds of metabolic syndrome. Your report may express VAT as a mass in grams, an index, or a percentage.
Lean mass, particularly in the arms and legs, is reported as the appendicular lean mass index (ALMI), which adjusts your muscle mass for your height. Low muscle mass, a condition called sarcopenia, is generally flagged at an ALMI below about 5.4 to 6.0 kg/m² in women or below 7.0 to 7.2 kg/m² in men, depending on which guidelines your provider uses. If your ALMI falls near or below these cutoffs, it’s a signal that building muscle through resistance exercise and adequate protein intake could meaningfully improve your health.
Reading Results for Children and Younger Adults
DEXA results for children and premenopausal women or men under 50 are interpreted differently. T-scores should not be used in pediatric reports at all, and neither should the terms “osteopenia” or “osteoporosis” on their own. Instead, the Z-score is the standard. A Z-score of -2.0 or lower in a child is described as “low bone mineral density for age” rather than osteoporosis.
In children, a diagnosis of osteoporosis requires both a Z-score of -2.0 or lower and a history of significant fractures: two or more long bone fractures before age 10, or three or more at any age up to 19. A single vertebral compression fracture can also indicate osteoporosis in a child, even without a low Z-score. The key point is that low bone density alone in a young person isn’t automatically a diagnosis. It needs clinical context.
How Often to Repeat Scans
If your initial scan shows normal bone density, you generally won’t need another for several years. Screening is recommended for all women at age 65, and for postmenopausal women under 65 who have risk factors like a family history of fractures, low body weight, or smoking. Men don’t have a routine screening recommendation from the U.S. Preventive Services Task Force, though individual risk factors may warrant testing.
If you’re being treated for osteoporosis or monitoring osteopenia, follow-up scans are typically done every one to two years. When comparing scans over time, make sure they’re done on the same machine at the same facility. Different machines can produce slightly different readings, making it hard to tell whether a change is real. And remember the 0.03 g/cm² threshold: changes smaller than that between scans may not reflect actual bone loss or improvement.