Cross-Calibrated Dual-Energy X-Ray Absorptiometry Scanners Demonstrate Systematic Bias in Pediatric and Young Adult Females

Consistency of dual-energy X-ray absorptiometry (DXA) scan results is critical for data integrity. For pediatric subjects, the extent to which cross-calibration of DXA scanners alleviates model-to-model scanner differences is unclear. In the current study, DXA bone outcomes were compared for same-day measurements performed using different scanners, cross-calibrated to alleviate discrepancies (Hologic; Discovery A [DISCO] and QDR 4500W [QDR]). Interscanner differences were evaluated in approximately 130 females aged 8-24 yr. Scans were performed in a single session on both QDR and DISCO scanners to compare projected area, bone mineral content, and areal bone mineral density (BMD) outputs for the whole body (total, subhead, head, arm, and leg), forearm (1/3 and ultradistal radius), lumbar spine (vertebra L3 and L1-L4), and proximal femur (femoral neck). Paired t tests evaluated interscanner differences; concordance correlation coefficients (CCCs) evaluated interscanner correlations. Root mean square error coefficients of variation were compared to same-day duplicate DISCO scan root mean square error coefficients of variation for approximately 30 adult females. Deming regression equations were generated for conversion of QDR to DISCO results and vice versa. Interscanner correlations were very high (95% confidence interval for CCC > 0.90), for all outcomes except for femoral neck area and subhead area (95% confidence interval for CCC = 0.83-0.94, 0.57-073). However, QDR values were systematically lower than Discovery values (p < 0.05), except for head area, head bone mineral content, head BMD, ultradistal BMD (QDR > Discovery, p <= 0.05) and L1-LA area, L3 area, and femoral neck BMD (no differences). Most Bland-Altman and Deming regression plots indicated good interscanner agreement, with little systematic variation based on bone or body size. In pediatric and young adult females, subtle but systematic differences were noted between scans obtained on DISCO and QDR scanners, despite cross-calibration, such that most outcomes are systematically higher for DISCO than for QDR. The use of conversion equations is warranted.