What are the interpretations and treatment options for T score screening results in osteoporosis?

T-Score Interpretation and Management in Osteoporosis

Diagnostic Classification by T-Score

The World Health Organization defines osteoporosis as a T-score ≤ -2.5 at the lumbar spine, femoral neck, or total hip measured by DXA, which is the gold standard for diagnosis. 1

The diagnostic thresholds are:

• Normal bone density: T-score ≥ -1.0 1, 2
• Osteopenia (low bone mass): T-score between -1.0 and -2.5 1, 2
• Osteoporosis: T-score ≤ -2.5 1, 2

Use the lowest T-score from any recommended measurement site (lumbar spine L1-L4, femoral neck, total hip, or one-third radius) for diagnostic classification. 3, 2

Critical Exception: Fragility Fracture Overrides T-Score

A fragility fracture establishes an osteoporosis diagnosis regardless of T-score, eliminating the need for DXA measurement. 3, 1 This includes:

• Hip fractures at any T-score 1, 4
• Vertebral fractures (even with T-scores in the osteopenic range) 3, 5, 4
• Proximal humerus, pelvis, or certain wrist fractures in patients with osteopenia 4

Approximately 50% of fragility fractures occur in postmenopausal women with T-scores > -2.5 (osteopenic range), highlighting that T-score alone does not capture all fracture risk. 2

Treatment Decisions Based on T-Score

For T-Score ≤ -2.5 (Osteoporosis)

Initiate pharmacologic treatment immediately with oral bisphosphonates as first-line therapy. 5

• Alendronate 70 mg weekly or alendronate 10 mg daily increases lumbar spine BMD by 2.8-5.3% and reduces vertebral fracture risk by 68% at 3 years 6, 7
• Denosumab 60 mg subcutaneously every 6 months reduces new vertebral fractures by 68%, hip fractures by 40%, and nonvertebral fractures at 3 years 6
• If oral bisphosphonates are contraindicated or not tolerated, use parenteral therapy (denosumab or intravenous bisphosphonates) 5

For T-Score Between -1.0 and -2.5 (Osteopenia)

Calculate 10-year fracture probability using FRAX, which incorporates hip BMD, age, gender, weight, family history of hip fracture, smoking, glucocorticoid use, and rheumatoid arthritis. 2

Treat if FRAX shows:

• 10-year hip fracture probability ≥ 3%, OR
• 10-year major osteoporotic fracture probability ≥ 20% 2

If FRAX thresholds are not met, implement non-pharmacologic interventions:

• Weight-bearing exercise 3, 2
• Calcium 1000-1200 mg/day 3, 2
• Vitamin D 800-1000 IU/day 3, 2
• Repeat DXA in 2 years 3

For T-Score > -1.0 (Normal)

Routine monitoring is appropriate; repeat DXA in 2 years. 3, 2 Focus on lifestyle modifications including smoking cessation, alcohol reduction if excessive, adequate nutrition, and regular weight-bearing exercise. 3

Special Populations and Contexts

Glucocorticoid-Induced Osteoporosis

Fractures occur at higher BMD levels in glucocorticoid-induced osteoporosis, so initiate treatment at T-score ≤ -1.5 rather than -2.5. 5

For patients on prednisone ≥ 5 mg daily (or equivalent) for ≥ 3 months:

• Perform DXA measurement 3
• Start treatment if T-score ≤ -1.5 5
• In patients ≥ 65 years, treatment can be initiated without DXA since the vast majority will have T-scores ≤ -1.5 5

Chronic Liver Disease

Perform DXA in patients with:

• Cirrhosis (clinical or histologic) 3
• Severe cholestasis (bilirubin > 3× upper limit of normal for > 6 months) 3
• Risk factors including oral prednisolone ≥ 5 mg for 3 months, hypogonadism, height loss > 4 cm, x-ray evidence of osteopenia, maternal hip fracture < 60 years, or BMI < 19 kg/m² 3

Premenopausal Women and Men < 50 Years

Use Z-scores (comparison to age-matched peers) rather than T-scores for assessment. 3, 2 A Z-score ≤ -2.0 suggests bone density below expected range for age and warrants investigation for secondary causes. 2

Measurement Sites and Technical Considerations

Primary DXA measurement sites are:

• Lumbar spine (L1-L4): measures up to 4 vertebral bodies 3, 1
• Hip: femoral neck and total hip 3, 1
• Forearm (one-third radius): used when spine and hip cannot be measured 3

Ensure follow-up scans are performed on the same DXA scanner using identical protocols, as vendor differences prohibit direct comparison unless cross-calibration has been performed. 2

Common Pitfalls to Avoid

Major clinical pitfall: Only 6.7% of patients undergo DXA within 6 months of a fragility fracture, and only 8% of patients on long-term corticosteroids receive follow-up DXA. 1 This represents massive underutilization of screening.

Additional workup when T-score ≤ -2.5:

• Thyroid function tests 3
• Corrected serum calcium and phosphate 3
• 25-OH vitamin D level (especially if housebound or malabsorption present) 3
• Sex hormones if hypogonadism suspected (estradiol/LH/FSH in women; testosterone/SHBG/LH/FSH in men) 3
• Lateral spine radiographs if clinical suspicion of vertebral fracture (kyphosis, height loss, back pain) 3