29th April 2024

Diagnosis

The World Health Organization (WHO) has defined diagnostic thresholds for low bone mass and osteoporosis based upon Bone mineral density (BMD) measurements. A patient’s BMD is compared with a young-adult reference population. Values are quantified using a T-score.

Clinical diagnosis of osteoporosis can be made based on the presence of:

• Fragility fracture, particularly at the spine, hip, wrist, humerus, rib or pelvis OR
• T-score ≤ -2.5 standard deviations (SDs) at any site based upon BMD measurement by dual-energy X-ray absorptiometry (DXA)

Alternatively, fracture risk can be assessed using the FRAX (Fracture Risk Assessment Tool), which is a computer-based calculator that estimates the 10-year probability of major osteoporotic fracture or hip fracture. A diagnosis of osteoporosis may be made if the 10-year probability of major osteoporotic fracture is ≥20% or the 10-year probability of hip fracture is ≥3%.

Measurements taken of the spine or hip are recommended as fractures are more likely at these sites. Spine BMD can be more useful if pharmacological therapy is planned as it shows less variability than other sites, and response to therapy can be detected earlier in the spine.

A T-score that is 1 to 2.5 SD below the young adult mean is termed low bone mass (osteopenia). Normal bone density is defined as a value within 1 SD of the mean value in the young adult reference population