Cross-Calibration of Lunar DPX-IQ and DPX Dual-Energy X-Ray Densitometers for Bone Mineral Measurements in Women

When dual-energy X-ray absorptiometry (DXA) instruments are replaced, it is essential to determine if systematic differences in measurements occur. As a part of the Kuopio Osteoporosis Risk Factor and Prevention study (N = 14,220), a group of women, aged 36 to 69 yr underwent anteroposterior lumbar spine L2 to L4 (n = 89) and proximal femur scans (n = 88) by the Lunar DPX and DPX-IQ, respectively, during the same visit. A high linear association (r from 0.944 to 0.989, p < 0.001) between the two scanners was established for lumbar spine and proximal femur bone mineral density (BMD). The average DPX values for BMD were 1.1% and 2.0% higher than those of DPX-IQ for the lumbar spine (p < 0.001) and Ward's triangle (p = 0.001), respectively. Femoral neck BMD values by the DPX were 1.4% lower (p < 0.001) compared to DPX-IQ. The difference between trochanter BMD results (0.1%) was not significant (p = 0.809). In the femoral neck and trochanter, but not in the lumbar spine or Ward's triangle, the differences in BMD values of the two machines were found to depend on body mass index. After linear formulas based on simple and multivariate linear regression analyses were calculated, the differences were negligible, enabling objective comparison of longitudinal measurements.