6.2 WHO Diagnostic Criteria & Population Application
Key Takeaways
The WHO international reference standard is a femoral neck T-score of −2.5 or lower. ISCD also permits diagnosis using the PA lumbar spine, total hip, and the one-third radius when indicated.
Classify postmenopausal women and men aged 50 or older using the lowest valid diagnostic T-score. ISCD also permits WHO criteria in women in the menopausal transition.
ISCD prefers Z-scores in women before menopause and men younger than 50. A Z-score of −2.0 or lower is below the expected range for age.
For a child with short stature or growth delay, adjust the PA spine result using bone mineral apparent density or height Z-score and adjust total body less head using height Z-score.
PA spine and total body less head are preferred for most children. Proximal femur, one-third radius, and lateral distal femur may be useful for specific clinical indications when appropriate reference data are available.
Choose the diagnostic framework before applying a threshold
Bone mineral density (BMD) from dual-energy X-ray absorptiometry (DXA) supports three distinct judgments. First decide whether the patient's images and regions of interest are valid. Then choose the score and diagnostic vocabulary appropriate for the patient. Finally, consider the fracture history and other risk factors that affect the clinical assessment. Each decision uses different information.
The World Health Organization (WHO) international reference standard for osteoporosis is a femoral neck T-score of −2.5 or lower, based on the young-adult White female NHANES III reference. The International Society for Clinical Densitometry (ISCD) applies densitometric classification in postmenopausal women and men aged 50 or older and permits several additional DXA sites. ISCD also permits use of the WHO criteria in women in the menopausal transition.
Classify adult DXA using valid measurements
| Densitometric category | T-score |
|---|---|
| Normal BMD | −1.0 or higher |
| Low bone mass | Below −1.0 and above −2.5 |
| Osteoporosis | −2.5 or lower |
| Severe or established osteoporosis | −2.5 or lower with one or more fragility fractures |
ISCD prefers low bone mass or low bone density to osteopenia. These categories describe the measured BMD relative to a reference population. A single examination cannot establish how much bone the patient has lost over time. Fracture probability also depends on factors such as age, prior fracture, and medications. A normal BMD classification can coexist with substantial fracture risk.
A low-energy mechanism, such as a fall from standing height, suggests a fragility fracture. Assess the mechanism and any evidence of a focal pathological process before classifying the fracture. In its U.S. guidance for postmenopausal women and men aged 50 or older, the Bone Health and Osteoporosis Foundation (BHOF) recommends considering treatment after a hip or vertebral fracture regardless of BMD. A patient can therefore meet a clinical treatment indication even when the T-score falls outside the densitometric osteoporosis range.
Regions of interest
- Posterior-anterior (PA) lumbar spine. Analyze L1 through L4 using every evaluable vertebra. Local structural change or artifact can invalidate a vertebra. ISCD permits exclusion when it is clearly abnormal and non-assessable within the system's resolution or when its T-score differs from adjacent vertebrae by more than 1.0. Use the software-derived T-score based on the BMD of the remaining vertebrae. At least two evaluable vertebrae are needed. With one remaining, use another valid skeletal site for diagnosis.
- Femoral neck and total hip. Use the lower valid T-score. If both hips were scanned, consider the valid femoral neck and total hip results from both sides. A trochanteric subregion or Ward's area does not supply a diagnostic score.
- One-third (33%) radius. Use the non-dominant forearm for adult diagnosis when indicated. Indications include an unmeasurable or uninterpretable hip or spine, hyperparathyroidism, or weight exceeding the DXA table limit. Other forearm regions and the lateral lumbar spine do not qualify for WHO classification. A validated young-adult reference is required if the one-third radius is measured by a peripheral DXA device.
- Other technologies. Apply the WHO thresholds only to equivalent measurements. Heel ultrasound scores and volumetric spinal quantitative computed tomography (QCT) values use different scales. ISCD recognizes an exception for equivalent femoral neck and total hip T-scores calculated from validated two-dimensional projections of hip QCT.
Worked example
A 66-year-old woman has a valid PA spine T-score of −1.8, total hip of −1.4, and femoral neck of −2.6. Use the femoral neck to report the overall densitometric classification of osteoporosis. If she has no known fragility fracture, the densitometric result does not establish the severe or established category. If the neck measurement is invalid because of hardware, exclude that result and classify using the remaining valid measurements, adding a description of the limitation.
Interpret BMD in younger adults
ISCD prefers Z-scores in women before menopause and men younger than 50. Use a population-specific age- and sex-appropriate reference when adequate data exist, with self-reported ethnicity for the Z-score calculation. A Z-score of −2.0 or lower is below the expected range for age. A higher Z-score is within the expected range for age. In a woman in the menopausal transition, the WHO diagnostic criteria may be used.
A report can identify low BMD for age and explain what warrants clinical evaluation. The adult ISCD positions expressly state that BMD alone cannot diagnose osteoporosis in men younger than 50. In premenopausal women, clinical assessment distinguishes low peak bone mass from active bone loss or established skeletal fragility. Consider low-trauma fractures and contributors such as prolonged amenorrhea, malabsorption, hypogonadism, or systemic glucocorticoids. A Z-score threshold plus a listed risk factor is insufficient as an automatic diagnostic rule. For example, report a lumbar Z-score of −2.1 in a 44-year-old premenopausal patient taking prednisone as below the expected range for age and assess her fracture and glucocorticoid history separately.
Interpret pediatric DXA in the context of growth and fractures
Use pediatric DXA when the result is likely to affect management and the child can be positioned safely. PA spine and total body less head (TBLH) are the preferred sites for most children. Use age-appropriate reference data that are valid for the scanner and software. Additional sites serve distinct needs.
| Site | Clinical use when suitable reference data are available |
|---|---|
| Proximal femur | Reduced lower-extremity loading or continuity of measurements into adulthood for a child at risk of bone fragility |
| One-third radius | An ambulatory child who cannot be scanned at other skeletal sites |
| Lateral distal femur | Lower-extremity fragility assessment in a nonambulatory child or monitoring changes in weight-bearing. It can also be useful when hardware, deformity, or positioning prevents other acquisitions. |
DXA measures bone mineral projected over an area. A smaller skeleton can therefore give a lower areal BMD even when the tissue has similar volumetric density. For a child with short stature or growth delay, adjust the spine result with bone mineral apparent density (BMAD) or height Z-score. Adjust TBLH using height Z-score. Use pediatric Z-scores and report the growth adjustment. Use low bone mineral mass or bone mineral density for a Z-score of −2.0 or lower. Pediatric reports omit T-scores and the term osteopenia.
A vertebral compression fracture supports a pediatric osteoporosis diagnosis when there is no local disease or high-energy trauma, regardless of the BMD result. Without such a fracture, the diagnosis requires a BMD Z-score of −2.0 or lower and a clinically significant fracture history. The latter means at least two long-bone fractures by age 10 or at least three by age 19. A Z-score above −2.0 can coexist with skeletal fragility.
| Patient group | Report | Determine next |
|---|---|---|
| Postmenopausal women and men aged 50 or older | Overall densitometric category from the lowest valid diagnostic T-score | Whether fracture history or absolute risk changes clinical management |
| Premenopausal women and men younger than 50 | Whether the Z-score is below or within the expected range for age | Whether there is evidence of skeletal fragility or a secondary cause |
| Children and adolescents | Pediatric Z-score, site, and growth adjustment if indicated | Whether the vertebral or long-bone fracture criteria are met |
ISCD Adult Official Positions · ISCD Pediatric Official Positions · BHOF Clinician's Guide
A 44-year-old premenopausal woman with lupus who takes prednisone has a PA lumbar spine T-score of −2.6 and Z-score of −2.1. Her femoral neck T-score is −1.8 and Z-score is −1.4. How should her lumbar spine DXA result be reported according to the ISCD adult positions?
Within the expected range for age based on the femoral neck Z-score.
Low bone mass based on the femoral neck T-score.
Densitometric osteoporosis based on the PA spine T-score.
Below the expected range for age based on the PA spine Z-score. Consider her fracture history and glucocorticoid exposure in the clinical assessment.
A 68-year-old postmenopausal woman has severe osteophytosis and facet sclerosis that make L2, L3, and L4 clearly non-assessable. L1 alone has a T-score of −2.7 and the unedited L1–L4 composite is −0.5. The valid femoral neck T-score is −2.6 and the valid total hip T-score is −2.1. She has no known fragility fracture. What is her densitometric classification?
Osteoporosis, based on the valid femoral neck T-score of -2.6, with the lumbar spine deemed uninterpretable for diagnosis.
Normal bone mass, based on the L1-L4 composite T-score of -0.5.
Low bone mass (osteopenia), based on the total hip T-score of -2.1.
Severe osteoporosis, based on the discordance between L1 and adjacent degenerative vertebrae.
Which set of findings satisfies the official ISCD pediatric criteria for establishing a definitive diagnosis of osteoporosis in a 13-year-old adolescent boy?
A Total Body Less Head (TBLH) size-adjusted Z-score of -2.3 in an asymptomatic child with no prior history of fractures.
A documented vertebral compression fracture without high-energy trauma or local vertebral disease.
A femoral neck Z-score of -2.6 combined with a single distal radius fracture sustained while playing soccer.
A lumbar spine T-score of -2.7 and a documented history of severe asthma treated with inhaled corticosteroids.
Sections you finish are checked off in the contents.