DEXA Data Interpretation & Reporting 3 — Questions and Answers
Question 1: When should vertebral levels be excluded from the lumbar spine BMD calculation in a DEXA report?
- When BMD at that level is below -2.5
- When a vertebra shows artifactual elevation due to osteophytes, fracture, or overlying hardware (Correct answer)
- When the patient has scoliosis greater than 5 degrees
- When only two vertebrae can be analyzed
Correct answer: When a vertebra shows artifactual elevation due to osteophytes, fracture, or overlying hardware
Vertebrae affected by artifacts such as osteophytes, fractures, or hardware should be excluded because they falsely elevate BMD readings.
Question 2: A 35-year-old man has a lumbar spine T-score of -2.6. According to ISCD guidelines, how should his bone density be classified?
- Osteoporosis
- Osteopenia
- Below the expected range for age — reported as low bone mass (Correct answer)
- Normal, as T-scores don't apply to men under 50
Correct answer: Below the expected range for age — reported as low bone mass
ISCD recommends using Z-scores (not T-scores) for premenopausal women and men under 50, reporting as 'below the expected range for age' if Z-score ≤ -2.0.
Question 3: On a DEXA printout, the precision error (CV%) at a facility is 1.5% for lumbar spine BMD. What does this metric represent?
- Accuracy of the DEXA scanner compared to pQCT
- Reproducibility of repeated BMD measurements at that facility (Correct answer)
- Difference between patient BMD and population mean
- Percentage of body fat measured
Correct answer: Reproducibility of repeated BMD measurements at that facility
Coefficient of variation (CV%) describes the reproducibility or precision of repeated measurements at a specific facility.
Question 4: A patient's hip scan shows asymmetric positioning artifacts. Which step should the technologist take before issuing the report?
- Average both hips and report that value
- Note the artifact in the report and rescan if the rotation exceeds acceptable limits (Correct answer)
- Use only Ward's triangle for the final BMD value
- Apply a 5% correction factor to the T-score
Correct answer: Note the artifact in the report and rescan if the rotation exceeds acceptable limits
Rotation artifacts can falsely alter BMD; the scan should be repeated if positioning errors exceed acceptable limits, and artifacts must be documented.
Question 5: Which Trabecular Bone Score (TBS) category indicates degraded microarchitecture on a DEXA report?
- TBS > 1.350
- TBS 1.200–1.350
- TBS < 1.200 (Correct answer)
- TBS > 1.500
Correct answer: TBS < 1.200
A TBS below 1.200 is classified as degraded bone microarchitecture, while 1.200–1.350 is partially degraded and above 1.350 is normal.
Question 6: In a serial DEXA report, the phrase 'statistically significant decrease in BMD' should only be used when:
- Any decrease in T-score is observed
- The BMD change exceeds the facility-specific Least Significant Change (LSC) (Correct answer)
- The patient's physician requests it
- The Z-score drops below -2.0
Correct answer: The BMD change exceeds the facility-specific Least Significant Change (LSC)
A statistically significant change is defined as BMD change exceeding the LSC, which accounts for measurement precision at that specific facility.
Question 7: A DEXA report states that a patient's forearm (33% radius) T-score is -2.6 and lumbar spine T-score is -1.4. Which value should drive the osteoporosis diagnosis?
- Lumbar spine, as it is the primary site
- Forearm, as it shows the lowest T-score of -2.6 (Correct answer)
- Neither — both must be ≤ -2.5 for diagnosis
- The average of both sites
Correct answer: Forearm, as it shows the lowest T-score of -2.6
Osteoporosis is diagnosed using the lowest T-score across all measured sites; a forearm T-score of -2.6 qualifies.
DEXA Data Interpretation & Reporting 3
When should vertebral levels be excluded from the lumbar spine BMD calculation in a DEXA report?