What is the significance of a large discrepancy in T-scores from a Dual-Energy X-ray Absorptiometry (DXA) scan, with a T-score of 4.1 at the spine, -1.8 at the femoral neck, and -0.8 at the total hip?

From the Guidelines

The large discrepancy in T-scores from your DXA scan is likely due to degenerative changes in the spine, and the hip measurements are more reliable for assessing your true bone status. The extremely high spine T-score of 4.1 is almost certainly caused by osteoarthritis, facet joint hypertrophy, aortic calcification, or other structural changes that artificially elevate the bone mineral density reading, as discussed in the updated practice guideline for dual-energy x-ray absorptiometry (DXA) 1. With a femoral neck T-score of -1.8, you have osteopenia (low bone mass) but not osteoporosis, according to the World Health Organization (WHO) definition of osteoporosis, which is based on a T-score of − 2.5 or lower in the lumbar spine, femoral neck, total hip, or one-third radius 1. Some key points to consider:

• The hip measurements are more reliable for assessing bone status in the presence of degenerative changes in the spine 1.
• Osteopenia is defined as a T-score between -1.0 and -2.5, and osteoporosis is defined as a T-score ≤ -2.5 1.
• The American College of Radiology (ACR) recommends pharmacologic treatment for all postmenopausal women and men >50 years of age with a T-score ≤ -2.5 1.
• A fracture risk assessment tool, such as FRAX, can be used to assess the risk of fracture in patients with low bone mass 1. I recommend focusing on bone health through adequate calcium intake (1000-1200mg daily), vitamin D supplementation (800-1000 IU daily), weight-bearing exercise, and fall prevention strategies. Discuss these results with your doctor, who may recommend a follow-up DXA scan in 1-2 years to monitor for changes, as suggested by the updated practice guideline for dual-energy x-ray absorptiometry (DXA) 1. If you have additional risk factors for fracture, medication might be considered despite not meeting the osteoporosis threshold, as recommended by the National Osteoporosis Foundation (NOF) 1. The artificial elevation in spine readings is common with aging and doesn't represent actual bone strength, which is why multiple measurement sites are used in bone density testing 1.

From the Research

Significance of T-Score Discrepancy

• A large discrepancy in T-scores from a Dual-Energy X-ray Absorptiometry (DXA) scan, with a T-score of 4.1 at the spine, -1.8 at the femoral neck, and -0.8 at the total hip, indicates a significant difference in bone mineral density between the spine and hip measurement sites 2, 3, 4.
• This discrepancy can be classified as major discordance, which is defined as a difference between the T-score categories of the femur and spine in the same individual, resulting in different diagnostic categories according to the World Health Organization classification system 2, 3, 4.
• Studies have shown that T-score discordance between the spine and hip is a common phenomenon, with prevalence rates ranging from 31.5% to 45.7% 2, 3, 4, 5.
• The causes of T-score discordance can be attributed to various factors, including physiologic and pathologic patient factors, as well as the performance or analysis of DXA itself 2, 3, 4.

Risk Factors for T-Score Discordance

• Age, menopause, and obesity have been identified as risk factors against T-score discordance in some studies 3, 4.
• However, other studies have found that only menopause was a significant risk factor against T-score discordance 3.
• The age at fracture has also been found to be a factor related to T-score discordance in patients with osteoporotic vertebral compression fractures 5.
• Further research is needed to fully understand the risk factors for T-score discordance and its clinical significance 5.

Clinical Implications

• Clinicians should be aware of the potential for T-score discordance between the spine and hip measurement sites and take this into account when interpreting DXA results and making diagnostic decisions 2, 3, 4.
• T-score discordance can have significant implications for the diagnosis and treatment of osteoporosis, and clinicians should be cautious when interpreting DXA results in patients with discordant T-scores 2, 3, 4.