There is no universal recommendation for when to repeat BMD in low risk patients

We agree with most guidelines suggest reevaluating fracture risk in 2-4 years, erring closer to two years with relatively higher fracture risk or lower bone density

Bone-Density Testing Interval and Transition to Osteoporosis in Older Women (NEJM 2012) looks at this question.

• Question: How long does it take for 10% of women to transition to radiographic osteoporosis stratified by results of BMD testing?
• Results:
  • Normal BMD (T score -1.00 or higher) = ~17 years
  • Mild osteopenia (T score -1.01 to -1.49) = ~17 years
  • Moderate osteopenia (T score -1.50 to -2.00) = ~4.5 years
  • Advanced osteopenia (T score -2.01 to -2.49) = ~1 year