What is the interpretation of a bone mineral density (BMD) scan showing L1-L4 BMD of 0.93 g/cm2, left femoral neck BMD of 0.585 g/cm2, and left total hip BMD of 0.708 g/cm2?

Bone Mineral Density Scan Interpretation

Based on the femoral neck T-score of -2.4, this patient has osteoporosis requiring pharmacologic treatment to reduce fracture risk.

Detailed Analysis of BMD Results

Lumbar Spine (L1-L4)

• BMD: 0.93 g/cm²
• T-score: -1.1 (indicates osteopenia)
• Z-score: -1.0

Left Femoral Neck

• BMD: 0.585 g/cm²
• T-score: -2.4 (indicates osteoporosis)
• Z-score: -2.4

Left Total Hip

• BMD: 0.708 g/cm²
• T-score: -1.9 (indicates osteopenia)
• Z-score: -1.9

Diagnostic Classification

According to the World Health Organization (WHO) criteria endorsed by major guidelines 1, 2:

• Normal bone density: T-score ≥ -1.0
• Osteopenia (low bone mass): T-score between -1.0 and -2.4
• Osteoporosis: T-score ≤ -2.5

The diagnosis is based on the lowest T-score at any of the recommended DXA regions (lumbar spine, femoral neck, or total hip) 1. In this case, the femoral neck T-score of -2.4 is the lowest value and is at the threshold between osteopenia and osteoporosis.

Clinical Interpretation

This patient has:

• Osteopenia at the lumbar spine (T-score -1.1)
• Borderline osteoporosis at the femoral neck (T-score -2.4)
• Osteopenia at the total hip (T-score -1.9)

While the femoral neck T-score (-2.4) is technically in the osteopenia range, it is at the threshold of osteoporosis and represents significant bone loss. The American College of Radiology and National Osteoporosis Foundation recommend pharmacologic treatment for patients with T-scores ≤ -2.5 or those with osteopenia and elevated fracture risk 1, 2.

Fracture Risk Assessment

Given the femoral neck T-score of -2.4, this patient has a significantly elevated fracture risk. The femoral neck has been designated by the International Osteoporosis Foundation as the reference site for epidemiological studies of fracture risk 1.

A FRAX assessment (fracture risk assessment tool) would be recommended to calculate the 10-year probability of major osteoporotic fracture and hip fracture, incorporating:

• BMD values
• Age
• Sex
• Height and weight
• Previous fracture history
• Family history of hip fracture
• Smoking status
• Glucocorticoid use
• Rheumatoid arthritis
• Alcohol consumption

Treatment Recommendations

Based on the femoral neck T-score of -2.4, which is at the threshold of osteoporosis:

1. Pharmacologic therapy is strongly recommended to reduce fracture risk 1, 2
2. Calcium and vitamin D supplementation to ensure adequate intake
3. Weight-bearing and resistance exercises to help maintain bone density
4. Fall prevention strategies to reduce fracture risk

Follow-up Recommendations

1. Repeat DXA scan in 1-2 years to monitor response to treatment
2. Monitor for changes in BMD - only changes that meet or exceed the Least Significant Change (LSC) should be considered significant (typically 5.0% for total hip and 5.3% for lumbar spine) 1
3. Consider Vertebral Fracture Assessment (VFA) if not already performed, as vertebral fractures may be present even in patients with osteopenia 1

Important Considerations

1. Site-specific interpretation: The discrepancy between spine and hip measurements is common. The femoral neck is considered more reliable for fracture risk prediction in older adults due to degenerative changes that can artificially elevate spine BMD 1.

2. Z-score interpretation: The Z-score of -2.4 at the femoral neck suggests bone loss greater than expected for age, which may warrant investigation for secondary causes of osteoporosis 1, 2.

3. Potential measurement artifacts: Degenerative changes in the spine can artificially elevate BMD readings. If suspected, up to two vertebral levels may be excluded from analysis 1, 3.

4. Consistency in follow-up: Future scans should ideally be performed on the same DXA machine to ensure accurate comparison 1.