DEXA Scan Report: T-Score, Z-Score and Osteoporosis Explained
Short answer: on a DEXA scan report, the T-score compares your bones with a healthy young adult of the same sex, and the Z-score compares them with people your own age. A T-score of minus 1 or higher is usually read as normal, between minus 1 and minus 2.5 as osteopenia (thinner than ideal), and minus 2.5 or lower as osteoporosis. Your doctor reads it alongside your age, history and fracture risk, so the number is the start of the conversation, not the verdict.
In brief
- What it measures: bone mineral density, mostly at the lower spine and the hip.
- T-score: you vs a healthy 30-year-old. Used for women after menopause and men over about 50.
- Z-score: you vs people your age. Used for children, younger adults and women before menopause.
- Typical cut-offs: minus 1 and above normal, minus 1 to minus 2.5 osteopenia, minus 2.5 and below osteoporosis.
- See a doctor soon: sudden back pain after a minor fall, lost height, or a new stoop.
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A grey picture of your spine, another of your hip, and a table full of decimals with minus signs in front. Most people jump to the word at the bottom: normal, osteopenia or osteoporosis. That word matters. But the table above it shows where the weak spot is, and how worried to be.
What does a DEXA scan actually measure?
DEXA stands for dual-energy X-ray absorptiometry. ELI5 version: the machine shines two very weak X-ray beams through your body. Bone blocks more of the beam than soft tissue, and by comparing the two beams the machine works out how much mineral, mainly calcium, is packed into each square centimetre of bone. That figure is your bone mineral density, or BMD, written in g/cm².
You lie flat on a padded table for ten to twenty minutes while an arm passes over you. No tunnel, no injection, and a radiation dose that is a small fraction of a chest X-ray.
How to read the columns on a DEXA report
Most reports have a table for each site scanned. The columns look roughly like this:
| Column | What it means | How to read it |
|---|---|---|
| Region (L1 to L4, femoral neck, total hip) | Which bone was measured | L1 to L4 are the four lower back bones; the femoral neck is the narrow part at the top of the thigh bone |
| BMD (g/cm²) | The raw density number | Useful for comparing your own scans over time on the same machine |
| T-score | You vs a healthy young adult | The number used to label osteopenia or osteoporosis after menopause or after about 50 |
| Z-score | You vs people your own age and sex | A low Z-score hints that something other than ageing is thinning the bone |
The doctor usually goes by the lowest T-score among the lumbar spine, femoral neck and total hip. So if your spine is minus 1.2 but your femoral neck is minus 2.6, the report will say osteoporosis.
T-score vs Z-score: which one applies to you?
A T-score answers the question “how far is this bone from its best?” Bone density peaks around the late twenties and early thirties, then slowly falls, faster in women for several years after menopause. Each whole number on the scale is one standard deviation, a statistical step that simply means “noticeably different from average”.
A Z-score answers a different question: “is this bone thin for someone your age?” For a 35-year-old woman who still has periods, the T-score isn’t used to diagnose osteoporosis. The Z-score is. A Z-score of minus 2 or lower is often reported as “below the expected range for age”, and it nudges the doctor to look for a cause such as thyroid or parathyroid problems, low vitamin D, coeliac disease, long-term steroid medicines, very low body weight or missed periods.
The T-score asks how far you are from your best bone. The Z-score asks whether something besides age is taking it away.
Osteopenia vs osteoporosis: what the labels mean
Osteopenia isn’t a disease. It’s a zone, and a crowded one: many people over fifty land in it. It means the bones are thinner than a young adult’s but haven’t crossed the osteoporosis line. What happens next depends on your whole fracture risk, not only the number.
Osteoporosis means the bone is thin enough that it can break from a fall that a healthy bone would shrug off, like slipping off a charpai or stumbling on the bathroom step. Doctors also diagnose osteoporosis, whatever the T-score, if someone has already had a low-trauma fracture of the hip or spine.
Myth: osteoporosis only happens to thin old women
Women carry more risk after menopause, but men get osteoporosis too, usually a few years later, and it is checked far less often in them. Younger people can have thin bones from long steroid courses, eating disorders, thyroid excess, heavy smoking or drinking and too little sun. The myth sticks because the bent grandmother is the only picture most people have seen.
What makes the numbers low or falsely high?
Real reasons for low density include ageing, menopause, a small frame, family history, long periods indoors, low calcium or protein intake, inactivity, smoking, and certain medicines.
A spine reading can look better than the bone really is. Arthritis spurs, a squashed vertebra or calcium in the aorta (the big artery in front of the spine) can add “extra mineral” to the picture. When the spine and hip scores disagree a lot, the doctor usually trusts the hip. That’s why an older person’s spine T-score of plus 0.5 doesn’t always mean strong bones.
When a DEXA result means see a doctor today
You have sudden, sharp back pain after a minor fall, a cough, a sneeze or lifting something light, especially with a low T-score. That can be a vertebral compression fracture. Also go the same day for hip or groin pain after a fall with trouble standing or putting weight on the leg, or any new numbness, weakness in the legs or loss of bladder control with back pain; that last one is an emergency. Losing height (more than about 3 to 4 cm over time) or a new stoop needs a doctor soon. Never start, stop or change any bone medicine on your own; the doctor decides.
How to prepare for a DEXA scan
- Skip calcium pills on the morning of the scan if you take them, unless told otherwise, because an undissolved one can sit in the gut and blur the picture. Keep taking prescribed medicines as normal.
- Wait after barium or contrast tests. Tell the centre if you’ve had a barium swallow, CT with contrast or a nuclear scan in the past week or two.
- Wear clothes without metal: no zips, hooks, belts or underwire near the hips or waist. A shalwar with an elastic waist works well.
- Mention pregnancy or a chance of it, and any metal hip or spine implants.
- Use the same centre next time.
No fasting needed. If you want the food and sun side of bone health, the bones after 40 on a desi diet guide covers calcium sources, vitamin D and strength work, and calcium-rich desi foods vs a pill looks at the choice between food and supplements.
What to do while you wait to see the doctor
Whatever the label, walk daily, add simple strength work twice a week, get protein and calcium from food such as dahi, milk, paneer, daal and greens, and fall-proof the home: loose rugs, wet bathroom floors and dark stairs turn a thin bone into a broken one.
Vitamin D is often checked alongside a DEXA. If yours came back low, reading a vitamin D report explains the units. For more report guides, browse Lab Reports Decoded.
Surprising facts about bone density
Did you know? Bone is living tissue, and your skeleton is slowly rebuilt over roughly ten years, which is why exercise and food still matter at seventy. And height loss can itself be a clue: some people discover a spine fracture only because a tailor’s measurement changed.
DEXA scan questions people ask most
What is a normal T-score on a DEXA scan?
A T-score of minus 1.0 or higher is usually read as normal. Between minus 1 and minus 2.5 is osteopenia, and minus 2.5 or lower is osteoporosis. Your doctor interprets it with your age and history.
What is the difference between T-score and Z-score?
The T-score compares your bone with a healthy young adult; the Z-score compares it with people your age. T-scores are used after menopause and in men over about 50, Z-scores in younger people and children.
Is a T-score of minus 2 bad?
It falls in the osteopenia range, which is common after fifty. Whether it needs medicine depends on your overall ten-year fracture risk, often estimated with a calculator called FRAX that blends age, weight, smoking, steroid use and family history, so it’s a question for your doctor.
Can osteopenia be reversed?
Density can sometimes improve a little with exercise, enough protein and calcium, vitamin D and fixing a cause such as low weight. The bigger aim is stopping further loss and avoiding falls.
Do I need to fast before a DEXA scan?
No. Eat as normal. Just skip calcium pills that morning unless told otherwise, and wear clothing with no metal near the hips.
How often should a DEXA scan be repeated?
Commonly every one to two years if you’re on bone treatment or at high risk, and less often if the first scan was normal. Your doctor sets the gap.
What does “low bone mass for age” mean on a report?
It usually means a Z-score of minus 2 or lower. The bone is thinner than expected for your age, and the doctor may look for a cause such as thyroid, vitamin D or medicine effects.
Why did my bone density drop between two scans?
It may be real loss, or a difference in machine, positioning or centre. Small changes can sit within the machine’s error, so ask your doctor whether the change is meaningful.