What is the recommended interval for repeating a Dual-Energy X-ray Absorptiometry (DEXA) scan for a 65-year-old with normal bone density?

DEXA Scan Timing for 65-Year-Old with Normal Bone Density

For a 65-year-old with normal bone density, a repeat DEXA scan is not necessary for at least 3-5 years, as there is insufficient evidence that repeated BMD measurement improves fracture risk prediction over the original measurement. 1

Rationale for Extended Screening Intervals

• The US Preventive Services Task Force (USPSTF) indicates that evidence is lacking about optimal intervals for repeated screening, and whether repeated screening is necessary in a woman with normal BMD 1
• A prospective study of 4,124 women 65 years or older found that neither repeated BMD measurement nor the change in BMD after eight years was more predictive of subsequent fracture risk than the original measurement 1
• Due to limitations in testing precision, a minimum of two years is needed to reliably measure a change in BMD; however, longer intervals may be necessary to improve fracture risk prediction 1
• Cohort studies evaluating screening intervals suggest that repeating BMD testing at an interval of 4 to 8 years does not result in additional accuracy in predicting fractures 1

Factors Affecting Screening Intervals

• For individuals with normal bone density or mild osteopenia, repeat DEXA is recommended in 2-3 years 2
• BMD measurements do not need to be repeated routinely in patients with osteopenia unless the baseline T-score is < -2.0 or risk factors develop 1
• The mean rate of bone loss in people not receiving osteoporosis treatment is generally less than 1% per year 3
• For someone with normal baseline BMD and a rate of bone loss less than 1% per year, BMD change is not likely to exceed the least significant change in less than 3 years after the baseline test 3

Special Considerations for Higher Risk Individuals

• Shorter intervals between testing (1-2 years) are appropriate for patients at high risk for accelerated bone loss, such as those on glucocorticoid therapy 1
• Patients receiving treatment for osteoporosis should have follow-up DEXA scans at 1-2 year intervals to monitor treatment effectiveness 2
• The transition to osteoporosis occurs over shorter intervals for individuals with lower baseline T scores and older age (about 5 years for women with a baseline T score in the -1.50 to -1.99 range versus almost 17 years for those with normal BMD) 1

Clinical Approach for a 65-Year-Old with Normal BMD

1. Assess for new risk factors at each clinical encounter:

   • Development of conditions associated with bone loss 1, 2
   • New medications that affect bone metabolism 1, 2
   • Height loss > 4 cm or kyphosis development 1

2. Consider fracture risk assessment:

   • Use FRAX or other validated tools to calculate 10-year fracture risk 2
   • A 65-year-old white woman with no other risk factors has a 9.3% 10-year risk of any osteoporotic fracture 1

3. Schedule repeat DEXA scan:

   • With normal BMD and no new risk factors: repeat in 3-5 years 1, 3
   • If new risk factors develop: consider earlier repeat testing (1-2 years) 1, 2

Common Pitfalls to Avoid

• Repeating DEXA scans too frequently (less than 2 years apart) in patients with normal BMD is discouraged as it exposes patients to unnecessary radiation and costs without clinical benefit 1, 3
• Failing to recognize that scan intervals <1 year are not recommended under any circumstances 1
• Overlooking the development of new risk factors that might warrant earlier repeat testing 1, 2
• Not considering that different DXA machines may exhibit variation in measurements unless cross-calibration has been performed 1

In conclusion, for a 65-year-old with normal bone density, current evidence supports waiting 3-5 years before repeating a DEXA scan, while continuing to monitor for the development of new risk factors that might warrant earlier reassessment.