How should I interpret a dual‑energy X‑ray absorptiometry T‑score and manage osteoporosis or osteopenia in a 65‑year‑old postmenopausal woman?

Bone Density Interpretation and Management in a 65-Year-Old Postmenopausal Woman

T-Score Interpretation

Use the lowest T-score from any measured site (lumbar spine, femoral neck, or total hip) to classify bone density status. 1

• 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

The T-score represents the number of standard deviations your patient's bone mineral density (BMD) differs from a young, healthy reference population of the same sex. 1, 3 For postmenopausal women and men over 50, always use T-scores (not Z-scores) for diagnosis. 2

Critical caveat: A fragility fracture (hip, vertebral, proximal humerus, or pelvis) automatically establishes an osteoporosis diagnosis regardless of T-score. 4, 5 Do not wait for a T-score ≤ -2.5 if your patient has already sustained a low-trauma fracture.

Management Algorithm

Step 1: Calculate 10-Year Fracture Risk Using FRAX

Input the following into the WHO FRAX calculator: 1, 6

• Age, sex, BMI
• Femoral neck BMD (or leave blank if unavailable)
• Prior fragility fracture (yes/no)
• Parental hip fracture history
• Current smoking status
• Glucocorticoid use (≥3 months at ≥5 mg prednisone daily)
• Rheumatoid arthritis
• Secondary osteoporosis causes
• Alcohol intake (≥3 drinks daily)

Step 2: Determine Treatment Threshold

Initiate pharmacologic treatment if any of the following apply: 1

1. T-score ≤ -2.5 at spine, femoral neck, or total hip
2. Prior fragility fracture (hip, vertebral, proximal humerus, pelvis, or distal forearm with osteopenia)
3. Osteopenia (T-score -1.0 to -2.5) PLUS:
   • 10-year hip fracture risk ≥3% on FRAX, OR
   • 10-year major osteoporotic fracture risk ≥20% on FRAX

For osteopenic women at high fracture risk, discuss treatment benefits, harms, costs, and patient preferences before initiating therapy. 1

Pharmacologic Treatment Options

First-Line: Oral Bisphosphonates

Alendronate or risedronate are first-line agents for most postmenopausal women with osteoporosis. 1

• Alendronate: 70 mg orally once weekly
• Risedronate: 35 mg orally once weekly or 150 mg once monthly

Administration requirements: Take on empty stomach with 8 oz plain water, remain upright for 30-60 minutes, wait 30 minutes before eating. 1

Alternative Options

Denosumab 60 mg subcutaneously every 6 months if bisphosphonates are contraindicated (severe renal impairment with CrCl <35 mL/min, esophageal disorders) or not tolerated. 4

Critical warning: If denosumab is discontinued, immediately transition to a bisphosphonate to prevent rebound vertebral fractures from rapid bone loss. 4

Romosozumab may be considered for very high-risk patients (T-score ≤ -3.0 or recent fracture), but carries cardiovascular warnings and is limited to 12 months of therapy followed by transition to antiresorptive therapy. 7

Agents to AVOID

Do NOT use menopausal estrogen therapy, estrogen plus progestogen, or raloxifene for osteoporosis treatment. 1 These agents have unfavorable benefit-to-harm ratios compared to bisphosphonates.

Non-Pharmacologic Management (Universal for All Patients)

Prescribe the following regardless of treatment decision: 4

• Calcium: 1000-1200 mg daily (dietary plus supplement)
• Vitamin D: 800-1000 IU daily
• Weight-bearing exercise: 30 minutes most days
• Fall prevention: Home safety assessment, balance training, vision correction
• Smoking cessation: Mandatory counseling
• Alcohol limitation: <3 drinks daily

Evaluation for Secondary Causes

Before initiating treatment, order the following laboratory tests to identify treatable secondary causes: 6

• Serum 25-hydroxyvitamin D
• Serum calcium and phosphorus
• Parathyroid hormone (PTH)
• Thyroid-stimulating hormone (TSH)
• Complete blood count
• Comprehensive metabolic panel (including creatinine, liver enzymes)

Secondary causes are present in 44-90% of postmenopausal women with osteoporosis. 6 Common culprits include vitamin D deficiency, primary hyperparathyroidism, hyperthyroidism (including iatrogenic from levothyroxine over-replacement), and chronic glucocorticoid use. 6

Monitoring Strategy

Do NOT perform routine BMD monitoring during the first 5 years of pharmacologic treatment. 1 The evidence does not support that monitoring improves outcomes, and treatment decisions should not be altered based on BMD changes during therapy.

If monitoring is performed for specific clinical reasons (e.g., concern for non-adherence, suspected secondary cause): 4

• Repeat DXA in 1-2 years on the same machine using the same protocol
• Compare absolute BMD values (g/cm²), NOT T-scores or Z-scores
• Only changes exceeding the Least Significant Change (LSC) for that facility are clinically meaningful (typically 3-5%)

Consider vertebral fracture assessment (VFA) imaging at baseline, as vertebral fractures are often asymptomatic but represent the strongest predictor of future fractures. 4

Common Pitfalls to Avoid

• Do not diagnose osteoporosis in premenopausal women or men <50 years using T-scores—use Z-scores instead. 2
• Do not rely solely on T-scores without calculating FRAX for osteopenic patients, as many fractures occur in the osteopenic range. 2
• Do not use spine BMD in patients with vertebral fractures, severe osteoarthritis, or aortic calcification, as these falsely elevate BMD readings. 1
• Do not continue denosumab indefinitely without a transition plan, as discontinuation without bisphosphonate follow-up causes dangerous rebound bone loss. 4