skip to main content

DXA Least Significant Change — SCE Rheumatology MCQ

Instant feedback + full explanation. One question, done properly.

ModerateMetabolic Bone DiseaseDXA Least Significant ChangeSCE Rheumatology

A 65-year-old woman receiving treatment for osteoporosis undergoes repeat DXA after 2 years. Both examinations were performed on the same scanner at the same facility, with no technical limitations. Her femoral-neck BMD has increased from 0.620 to 0.628 g/cm², corresponding to a T-score change from −2.8 to −2.6. The facility-specific least significant change for femoral-neck BMD is 0.022 g/cm². Which is the most appropriate interpretation?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: B — No; the increase is below the facility's LSC and is compatible with measurement variability

The correct answer is B. Serial DXA change should be assessed using absolute BMD and the facility-specific least significant change, which incorporates local measurement precision. The observed increase is 0.008 g/cm², below the LSC of 0.022 g/cm²; it therefore cannot be distinguished confidently from measurement variability. A 0.2 change in T-score alone does not establish a significant biological response, making B incorrect. A 2-year interval may be clinically reasonable but does not eliminate precision error, so C is incorrect. Z-scores compare BMD with an age-matched population and are not the preferred measure of serial change, excluding D. Femoral-neck BMD can be followed when acquisition and analysis are technically comparable, so E is also incorrect.

Reference: Kendler DL et al. Repeating Measurement of Bone Mineral Density when Monitoring with Dual-energy X-ray Absorptiometry: 2019 ISCD Official Position. Journal of Clinical Densitometry. 2019;22(4):489-500. https://pubmed.ncbi.nlm.nih.gov/31378452/