What T score indicates osteoporosis?

Osteoporosis Diagnosis Based on T-Score

Osteoporosis is defined as a T-score of -2.5 or less at the lumbar spine, femoral neck, total hip, or one-third radius, according to the World Health Organization (WHO) criteria. 1

T-Score Classification System

The WHO classification system for bone mineral density (BMD) defines:

• Normal BMD: T-score greater than -1.0
• Osteopenia/low bone mass: T-score between -2.5 and -1.0
• Osteoporosis: T-score equal to or less than -2.5 2, 1

This classification applies to both men and women, with measurements typically obtained through dual-energy X-ray absorptiometry (DXA) 1.

Important Clinical Considerations

Diagnostic Overrides

• An osteoporotic fracture supersedes any DXA measurement
• Patients with T-scores in the osteopenic range who have a fragility fracture should be diagnosed with osteoporosis regardless of their T-score 1
• A diagnosis of osteoporosis may be presumed in the presence of a prior low-trauma major osteoporotic fracture, even with normal BMD 1, 3

Measurement Specifics

• DXA is the mainstay of bone densitometry and the clinically proven method for measuring BMD 2
• The T-score represents the number of standard deviations that the patient's BMD is above or below the mean in a young adult reference population 2
• The young adult Caucasian female normative reference database is recommended for T-score calculation for both women and men 1

Site-Specific Considerations

• The density of the total hip is the best predictor for hip fracture risk 4
• The lumbar spine is the best site for monitoring treatment effect 4
• Different skeletal sites may yield different T-scores in the same patient, potentially leading to discordant diagnoses 5

Treatment Thresholds

The National Osteoporosis Foundation recommends pharmacologic treatment for:

• All postmenopausal women and men over age 50 years with a T-score equal to or less than -2.5 2, 1
• Patients with osteopenia (T-scores between -1.0 and -2.5) who have a 10-year probability of hip fracture ≥3% or a 10-year probability of major osteoporotic fracture ≥20% based on FRAX 2, 1

Special Populations

• For younger individuals, the International Society for Clinical Densitometry recommends using Z-scores rather than T-scores
• A Z-score ≤ -2.0 is defined as "bone mineral density below the expected range for age" and should prompt investigation for secondary causes of osteoporosis 1
• Comprehensive evaluation for secondary causes is mandatory with a Z-score ≤ -2.0 1

Clinical Pitfalls to Avoid

• BMD measured by DXA can overestimate BMD in taller individuals and underestimate BMD in petite individuals 1
• T-scores alone do not capture all aspects of fracture risk; consider using FRAX for a more comprehensive assessment 1
• Different measurement techniques (DXA, QCT, ultrasound) and different skeletal sites may yield significantly different T-scores and prevalence estimates for osteoporosis in the same patient 5
• Using a single T-score criterion (-2.5) across all measurement techniques may be inappropriate, as this threshold was primarily established for DXA measurements 5

Remember that the diagnosis of osteoporosis should trigger appropriate treatment and lifestyle modifications to reduce fracture risk and improve patient outcomes.