• Use the lowest T-score at the lumbar spine, hip, and/or forearm (radius) to diagnose osteoporosis
• The forearm (radius) can be particularly useful in primary hyperparathyroidism

• Compares patient’s bone mineral density to that of a young-adult reference population (“normal”), and is reported as standard deviation (SD)
  • Normal is a bone density = 0 +/- 1
  • Osteopenia/low bone mass is = -1 to -2.4
  • Osteoporosis is lower than -2.5

• Compares patient’s bone mineral density to that of an aged-matched population, and is reported as standard deviation
• More useful in younger adult patients (premenopausal women, men <50, or children)
• A Z score < -2.0 should prompt evaluation of secondary causes

• There is an inherent variation on BMD measurements due to positioning and machine variation.
  • Attempt to use the same DXA machine in the same positioning
  • A change in BMD should consider what the specific “least significant change” is to account for precision errors
• A falsely high improved T score can result from a fracture or degenerative disease as the bone is “denser”!

1. Does not consider dose-responses for several risk factors
   • Examples: One vs multiple previous fractures, glucocorticoid exposure, smoking, alcohol use
   • May under- or over-estimate fracture risk
2. Only uses input from hip BMD
   • May underestimate risk of fracture where spine BMD is much lower than femur neck
3. The benefits of using FRAX in addition to just BMD to determine treatment thresholds has not been rigorously established in older adults, especially with the more novel (and more expensive) antiresorptive therapies
4. FRAX may underestimate fracture risk in non-white populations
   

PEARL: FRAX is a validated, standardized risk tool but should not replace a clinical risk assessment based on a comprehensive evaluation and decision to treat osteoporosis should be individualized.