Background: A significant loss in bone density and strength occurs during the post-renal-transplant period with higher susceptibility to fracture. The study aims to compare the performance of the Radiofrequency Echographic Multi Spectrometry (REMS) in the bone mineral density assessment with the conventional dual-energy X-ray absorptiometry (DXA) in a cohort of kidney transplant recipients (KTR). Methods: A cohort of 40 patients underwent both DXA and REMS examinations on the lumbar spine and/or proximal femur. The paired t-test was used to compare DXA and REMS measurements; the chi-square test was used to compare the prevalence of osteoporosis/osteopenia. The agreement between the two techniques was assessed through Spearman’s correlation. Results: As expected, most KTR patients were osteopenic or osteoporotic with both REMS and DXA (86.5% and 81% for the femur; 88% and 65% for the lumbar spine p < 0.05). A modest correlation (r = 0.4, p < 0.01) was observed at the lumbar spine between the T-score measured by REMS and DXA. A strong correlation was defined between REMS and DXA in the femoral region (r = 0.7, p < 0.0001). Conclusions: The study demonstrates the exchangeability of the two techniques on the proximal femur in KTR and a higher diagnostic accuracy of REMS at the spine level than DXA.

Summary In a peritoneal dialysis longitudinal cohort, REMS and DXA showed similar bone density, but only DXA detected significant cortical bone loss. REMS tended to give lower bone mineral density values and did not correlate with DXA changes. REMS may complement DXA when DXA findings are difficult to interpret or when closer longitudinal monitoring is needed, but larger studies are needed to define its role. Background Dual X-ray absorptiometry (DXA) is the gold standard for bone mineral density (BMD) assessment in chronic kidney disease patients, but it can have limited accuracy and radiofrequency echographic multi-spectrometry (REMS) may overcome some of its limitations. We aimed to evaluate and compare longitudinal BMD changes assessed by DXA and REMS in peritoneal dialysis (PD) patients. Methods Prospective cohort study including 20 PD patients that underwent two separate DXA and REMS evaluations. Clinical, biochemical, and imaging data, including abdominal aorta calcification (AAC) scores and fracture history, were collected. Longitudinal BMD changes were analyzed using linear mixed-effects models. Results Over a median follow-up period of 19.8 months, DXA revealed significant BMD declines at the femoral neck (FN) (−3.2%, p = 0.039) while REMS showed non-significant numerical declines. REMS consistently yielded lower BMD values than DXA at both lumbar spine (LS) and FN. The trajectories of BMD over time were similar between DXA and REMS for LS (p = 0.806) and FN (p = 0.229), regardless of whether patients were receiving anti-osteoporosis treatment and of the presence of fractures. However, there was no correlation of the annualized changes in BMD at the FN and LS between the two methods (r² = 0.001, p = 0.905, and r² = 0.001, p = 0.928, respectively). Conclusion DXA detected a significant decline in BMD at cortical sites, whereas REMS did not, and the correlation of the annualized changes between the two methods in assessing changes over time was poor. Given the small sample size, larger studies are needed to clarify the comparative and possible complementary roles of REMS and DXA in monitoring bone health in end-stage kidney disease.