Chulalongkorn Medical Journal


Background: When the department installed the new dual energy X-ray absorptiometry (DXA) system, cross calibration as the international society for clinical densitometry (ISCD) recommendation has to be implemented. The generalized least significant change (GLSC) and percentage of generalized least significant change (%GLSC) value must be determined for comparing the bone mineral density (BMD) values between 2 systems. Objective: To determine the generalized least significant change (GLSC) and %GLSC values and compare the BMD relationship between Hologic Horizon A and Discovery A through the cross calibration. Methods: Thirty women subjects (56 - 67 years) were scanned at the lumbar spine and femur on both systems. The linear regression and Bland-Altman analysis were used to reveal the relationship and agreement. The least significant change (LSC) was calculated on the individually DXA system and for cross-calibration between the two systems, the GLSC and %GLSC were presented. Results: The relationship was highly correlated in BMD. Bland-Altman analysis presented good agreement. The LSC values in lumbar spine, femoral neck, and total femur were 1.6%, 2.8% and 1.2% for Horizon A and 2.1%, 2.6% and 1.8% for Discovery A, respectively. The LSC of both systems in all sites were within the minimum acceptable precision according to the recommendation from ISCD. The GLSC and %GLSC values between two systems in lumbar spine, femoral neck, and total femur were 0.015 g/cm2 and 1.8%, 0.017 g/cm2 and 2.6%, and 0.013 g/cm2 and 1.6%, respectively. Conclusion: The stated GLSC from two different systems could be used to interpret the true change of the BMD, when the magnitude of the difference of BMD between systems is greater than the GLSC value.



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