Background: In renal transplant recipients, fracture risk is high and Bone Mineral Density (BMD) has been shown to be of poor predictive value for this risk. A confounding factor in the interpretation of BMD in these patients is calcification of the large vessels, with conventional anteroposterior (AP) lumbar spine (LS) BMD being potentially falsely increased due to inclusion of calcification in the assessment of BMD. Our objective was to evaluate the impact of vascular calcification on BMD by comparing standard AP LS BMD measurements to lateral LS BMD measurements, in which inadvertent inclusion of calcified large vessels in the area of calculation is precluded.
Methods: Pilot study in consecutive renal transplant recipients aged≧18 years who had lateral LS BMD measurements in addition to conventional AP LS and femoral neck BMD measurements. Vascular calcification was assessed on AP and lateral radiographs.
Results: Sixteen patients (10 female) were included with median age 56.9 years(range19.0-76.7). Mean LS BMD using AP DXA was significantly higher than LS BMD using lateral DXA (0.90g/cm2±0.15 vs. 0.53g/cm2±0.13, p<0.001). Mean FN BMD was 0.63g/cm2±0.11. The difference between AP and lateral LS BMD remained significant, also in the absence of significant vascular calcifications. Using conventional AP LS BMD, one patient had normal BMD, 8 had osteopenia and 7 had osteoporosis. Using lateral LS BMD, only one patient had osteopenia and 15 osteoporosis.
Conclusion: In patients with renal transplantation in whom vascular calcification is common, the significant discrepancy between AP and lateral LS BMD suggests that vascular calcification represents an important confounding factor in the interpretation of LS BMD. Whether eliminating this confounding factor by lateral DXA scans may increase the reliability of BMD measurements and thereby improve fracture risk prediction in this difficult to manage patient group remains to be established by studies including larger numbers of patients and long-term follow-up.
Disclosure: The authors declared no competing interests.