Importance of cross-calibration when replacing DXA scanners: QDR4500W and Discovery Wi.

The aim of the study was to determine reproducibility and extent of agreement between 2 dual-energy X-ray absorptiometers (Hologic QDR4500W, Discovery Wi). The average age of the sample (n = 42) was 50.4 (SD = 9.9) years old and 27.1 (SD = 6.1) kg/m2 body mass index. Four scans were performed with each subject (2 on each device) over approximately 3 weeks. Whole body, proximal femur, and spine scans were performed at each visit. Major variables were whole body bone mineral content (BMC), fat mass, and nonosseous lean mass, and bone mineral density (BMD) of total proximal femur, femoral neck, total spine. Bland and Altman plots assessed the extent of the agreement. Regression analysis was used to develop correction equations if indicated. Both devices demonstrated good precision for whole body composition and BMD of central sites (< 1% different). Interdevice agreement was acceptable for BMD of central sites (< 1% different), but there were systematic differences for whole body composition between the 2 devices. It was concluded that when replacing an existing scanner with a new model, in vivo cross-calibration is important to ensure comparability of scan data, especially for whole body composition.