What is the T score cutoff for diagnosing osteoporosis?

T-Score Cutoff for Osteoporosis Diagnosis

According to the World Health Organization (WHO) criteria, a T-score value less than or equal to -2.5 at the lumbar spine, femoral neck, total hip, or one-third (33%) radius is the diagnostic threshold for osteoporosis. 1

Diagnostic Classifications Based on T-scores

• Normal BMD: T-score ≥ -1.0
• Osteopenia/Low Bone Mass: T-score between -2.5 and -1.0
• Osteoporosis: T-score ≤ -2.5

These classifications are based on the lowest T-score at any of the recommended DXA regions of interest (ROIs) 1.

Special Populations and Considerations

Premenopausal Women and Men Under 50 Years

• The International Society for Clinical Densitometry (ISCD) recommends using Z-scores rather than T-scores for these populations 1, 2
• Z-score ≤ -2.0 is defined as "bone mineral density below the expected range for age" 1, 2
• However, the International Osteoporosis Foundation (IOF) recommends that a T-score ≤ -2.5 may be viewed as diagnostic of osteoporosis in younger individuals in the presence of skeletal fragility 1, 2

Fracture History

• An osteoporotic fracture supersedes any DXA measurement 1
• Patients with T-scores in the osteopenic range who have a fragility fracture should be diagnosed with osteoporosis regardless of their T-score 1
• Some societies (EANM, ASBMR, CSEM) have proposed that a diagnosis of osteoporosis may be presumed in the presence of a prior low-trauma major osteoporotic fracture, even with normal BMD 1

Men vs. Women

• The same T-score cutoffs apply to both men and women 1
• Use of the young adult Caucasian female normative reference database for T-score calculation is recommended for both women and men 1

Limitations of T-score Based Diagnosis

1. Diagnostic inconsistencies: T-scores can lead to diagnostic inconsistencies among different skeletal sites and low concordance with fragility fracture-based diagnosis 3

2. Technology differences: Different measurement techniques (DXA, QCT, ultrasound) can provide discrepant estimates of prevalence 4

3. Size artifacts: BMD measured by DXA can overestimate BMD in taller individuals and underestimate BMD in petite individuals 1

4. Beyond BMD: T-scores alone do not capture all aspects of fracture risk. The FRAX tool incorporates additional risk factors including age, sex, weight, family history, smoking, steroid use, and other clinical factors 1, 5

Clinical Implications

• The National Osteoporosis Foundation recommends pharmacologic treatment for all postmenopausal women and men >50 years of age with a T-score ≤ -2.5 1

• For patients with low bone mass (osteopenia), treatment decisions should be guided by absolute fracture risk assessment tools like FRAX 1, 5

• Treatment is recommended in patients with a 10-year probability of a hip fracture ≥3% or a 10-year probability of a major osteoporosis-related fracture ≥20% based on FRAX 1

Common Pitfalls to Avoid

1. Using T-scores for younger populations: Remember to use Z-scores for premenopausal women and men under 50

2. Ignoring fracture history: A fragility fracture indicates osteoporosis regardless of BMD

3. Relying solely on T-scores: Consider comprehensive fracture risk assessment, especially in patients with osteopenia

4. Overlooking secondary causes: When T-scores indicate osteoporosis, especially in younger individuals, evaluate for secondary causes

5. Inconsistent follow-up: When monitoring treatment, use absolute BMD values (g/cm²), not T-scores or Z-scores 1