Diagnosis & testing
Diagnosis rests on more than a single number. A DXA scan gives the T-score, FRAX turns risk factors into a 10-year fracture probability, and tools like the trabecular bone score and vertebral imaging catch the risk that density alone misses. Together they decide who is treated, and how.
Key takeaways
- DXA measures bone density; a T-score of −2.5 or below at the hip or spine defines osteoporosis.
- A fragility fracture diagnoses osteoporosis on its own — regardless of the T-score.
- FRAX estimates 10-year fracture probability and separates high from very-high risk.
- About half of women who fracture have T-scores outside the osteoporosis range — which is why we look beyond BMD.
- Osteoporosis is badly under-diagnosed and under-treated — most fragility fractures never trigger a bone workup, and men are missed even more often than women.
DXA & T-scores
The standard test for bone density is DXA (dual-energy X-ray absorptiometry) — a quick, low-radiation scan, usually of the hip and lumbar spine. It reports two comparisons:
- T-score — your density compared with a healthy young adult. This is what defines osteoporosis in postmenopausal women and older men.
- Z-score — your density compared with others your own age and sex. A Z-score well below expected prompts a search for secondary causes (see secondary causes).
| Category | T-score (hip or spine) |
|---|---|
| Normal | −1.0 or above |
| Low bone mass (osteopenia) | Between −1.0 and −2.5 |
| Osteoporosis | −2.5 or below |
| Osteoporosis (by fracture) | Any T-score, if a fragility fracture has occurred |
DXA is also how we track response to treatment over time. Because total-hip BMD predicts both hip and spine fracture risk most consistently, it's the density site we watch most closely (see goal-directed treatment).
FRAX & risk stratification
A T-score is a snapshot of density; FRAX turns the whole picture into risk. It combines age, sex, weight and height, prior fracture, parental hip fracture, smoking, glucocorticoid use, rheumatoid arthritis, other secondary causes, alcohol intake, and (optionally) femoral-neck BMD into a 10-year probability of a major osteoporotic fracture and of hip fracture.
Guidelines use these probabilities — together with fracture history and BMD — to sort patients into risk tiers, and the tier drives treatment:
High vs. very-high fracture risk
Guideline frameworkRoughly two-thirds of postmenopausal women over 50 fall into a low-to-moderate risk group where reassessment over time is appropriate; about a third are high to very high risk, where treatment is recommended to prevent a first or recurrent fracture.
One evolving refinement worth knowing: an ASBMR task force has recommended removing race and ethnicity as a variable in FRAX, since race-based adjustment is not a sound basis for individual risk estimation. As an interim step, non-White women can be shown a risk range rather than a single race-adjusted number. We read FRAX with that limitation in mind rather than treating one figure as precise.
Beyond BMD: trabecular bone score & imaging
Density is not the whole story. In a 2020 registry study of women who fractured after a baseline DXA, about half had T-scores outside the osteoporosis range — and among younger postmenopausal women, that figure rose to roughly three-quarters. "Normal" density clearly does not mean normal bone.
Two tools help close that gap:
- Trabecular bone score (TBS) — a texture measure derived from the same lumbar-spine DXA image that estimates microarchitecture. Adding TBS to BMD reclassifies risk: in that same study, it cut the share of women labeled "normal or borderline" from 54% to 32%. TBS also improves FRAX-based prediction.
- Vertebral fracture assessment (VFA) / spine imaging — because vertebral fractures are common and often silent (see a silent disease), finding one changes both the diagnosis and the urgency to treat.
For cliniciansHow we use TBS, VFA, and BMD together
We obtain TBS with lumbar DXA in patients whose fracture risk seems discordant with BMD (e.g., osteopenic T-scores with clinical risk factors, or type 2 diabetes, where BMD underestimates risk). VFA or lateral spine imaging is added for height loss, back pain, glucocorticoid exposure, or T-scores in the osteoporotic range, since an occult vertebral fracture reclassifies the patient to very high risk and often to an anabolic-first strategy. Total-hip BMD is our primary monitoring target given its consistent prediction of both vertebral and nonvertebral fracture.
Why screening matters: the diagnosis & treatment gap
Osteoporosis is common, serious, and — despite reliable tests and effective drugs — routinely missed. Roughly 2 million osteoporotic fractures occur in the US each year, more than heart attack, stroke, and breast and prostate cancer combined; about 1 in 2 women and up to 1 in 4 men over 50 will break a bone because of it. Yet most of that risk goes unrecognized until a fracture happens — and too often even after one.
The gap is wider in men. Men are screened less often than women even when they meet age criteria, are far less likely to get a bone-density scan after a hip fracture (about 5% of men vs. 12% of women), and are less likely to be treated afterward — partly because a man's fracture is more readily dismissed as a “high-trauma” accident.
When to get tested
Screening finds the disease before the fracture. General guidance:
- All women 65 and older, and all men 70 and older.
- Younger postmenopausal women and men 50–69 with risk factors (prior fracture, low body weight, steroid use, family history, and others — see Causes).
- Anyone 50 or older who breaks a bone — a fragility fracture warrants assessment regardless of age.
- Adults with a condition or medication known to cause bone loss.
How often to repeat DXA depends on your risk and whether you're on treatment — commonly every 1–3 years, tailored to the situation. We set the interval to the individual rather than a fixed calendar.
What this means for you
If you're due for screening — or you've fractured and never had a scan — ask for a DXA. Bring the actual report to any bone-health visit: the T-scores at each site, and any prior scans, let us judge change over time, which is often more informative than a single reading.
Have a DXA report you don't fully understand?
Bring it in. We'll walk through your T-scores, your FRAX risk, and whether you need treatment or monitoring.