DEXA Bone Density Scan Explained: T-Score, Osteoporosis and When to Repeat
DEXA is the reference standard for osteoporosis diagnosis. Learn T-score cut-offs, FRAX integration, and treatment thresholds.
DEXA measures bone mineral density (BMD) at lumbar spine and hip and reports a T-score. T-score ≥ −1.0 is normal; −1.0 to −2.5 is osteopenia; ≤ −2.5 is osteoporosis. Combine with FRAX to estimate 10-year fracture risk and guide treatment thresholds.
DEXA is a low-radiation X-ray technique (~0.001–0.01 mSv per site — much less than a chest X-ray). The WHO T-score system compares BMD to a healthy young adult reference. Z-scores (age-matched) are used in premenopausal women, men < 50, and children. NICE CG146 (updated) recommends DEXA in postmenopausal women and men > 50 with FRAX-defined risk factors, in adults on long-term (> 3 months) systemic corticosteroids, and in patients with fragility fracture. FRAX integrates BMD with age, sex, previous fracture, family history, smoking, alcohol, glucocorticoid exposure, secondary osteoporosis, and rheumatoid arthritis to give 10-year probability of major osteoporotic fracture and hip fracture. UK NOGG intervention thresholds guide treatment (bisphosphonate first-line; denosumab, zoledronate, romosozumab, or teriparatide for higher risk). Repeat DEXA every 1–3 years while on treatment; every 3–5 years in untreated at-risk patients. Vertebral fracture assessment (VFA) can be added to DEXA to detect silent vertebral fractures.
- Radiation
- ~0.001–0.01 mSv per site
- T-score normal
- ≥ −1.0
- Osteopenia
- −1.0 to −2.5
- Osteoporosis
- ≤ −2.5
- Score for < 50 y
- Use Z-score
T-score categories
| T-score | Category | Typical action |
|---|---|---|
| ≥ −1.0 | Normal | Lifestyle. Repeat 5 y if risk changes. |
| −1.0 to −2.5 | Osteopenia | FRAX. Treat if high risk / fragility fracture. |
| ≤ −2.5 | Osteoporosis | Treat unless contraindicated. |
| ≤ −2.5 + fragility fracture | Severe osteoporosis | Treat + consider anabolic agent (teriparatide/romosozumab). |
When to order DEXA
Postmenopausal women with clinical risk factors (FRAX-selected).
Men ≥ 50 with risk factors.
Adults on ≥ 5 mg prednisolone-equivalent for ≥ 3 months.
After any fragility fracture in an adult > 50.
Secondary osteoporosis risks: hypogonadism, malabsorption, hyperparathyroidism, chronic liver disease, anti-androgen or aromatase-inhibitor therapy.
- Fragility fracture at any site — start treatment without waiting for DEXA if T-score expected to be low.
- Vertebral fracture on imaging + acute back pain — pain management + osteoporosis pathway.
- On steroids long-term — early DEXA + bone-protective treatment.
Osteoporosis workup
- 1Fragility fracture in adult > 50?Treat now; DEXA to guide monitoring.
- 2FRAX intermediate?DEXA to refine.
- 3Osteoporosis + no contraindication?Bisphosphonate first-line.
- 4Very high risk / multiple vertebral fractures?Consider romosozumab or teriparatide.
Related questions people ask
Frequently asked questions
- DEXA is the reference standard for osteoporosis diagnosis.
- Combine with FRAX to estimate 10-year fracture risk.
- Treat fragility fractures without waiting for DEXA.
- Bisphosphonates first-line; anabolics for high-risk.
- Repeat 1–3 years on treatment.
References
2 sources- NOGGClinical Guideline for the Prevention and Treatment of Osteoporosis (2021)
UK NOGG guideline.
nogg.org.uk
- NICEOsteoporosis: assessing the risk of fragility fracture (CG146)
UK national guideline.
nice.org.uk
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