Abstract

Background Chronic kidney disease mineral and bone disorders (CKD-MBD) is often seen in end-stage renal disease and remain after renal transplantation. The bone-vascular axis hypothesis holds a plea for related pathophysiological mechanisms driving both bone-loss and vascular calcification, which contributes to excess cardiovascular risk in renal transplant recipients (RTR). We hypothesized that, in RTR, lower bone mineral density (BMD) is independently associated with higher abdominal aortic calcification (AAC). Methods From 2004 to 2014, RTR referred for a dual-energy X-ray absorptiometry (DXA) procedure within 6 months after transplantation were included in a retrospective, single-center study. Areal BMD was measured at the proximal femur, and AAC was quantified from lateral single-energy images of the lumbar spine by using an 8-point scoring system. Patients were divided into three AAC-categories (negative finding, low-AAC, and high-ACC; according to AAC-scores 0, 1-3 and 4-8, respectively). Multivariable-adjusted multinomial logistic regression models were performed to study the association between BMD and AAC. Results We included 678 RTR (51±13 years-old, 58% males, eGFR 51±15 mL/min/1.73 m2), of whom 366 (54%) had prevalent BMD disorders, and 266 (39%) had detectable calcification (AAC-score ≥1). AAC-categories distribution was different across subgroups by BMD (P<0.001), e.g., high-AAC was observed in 9%, 11% and 25% of RTR with normal, osteopenia, and osteoporosis BMD, respectively. Higher BMD (T-score, continuous) was associated with lower likelihood of prevalent high-AAC (OR 0.60, 95% CI 0.43-0.85; P=0.001), independent of age, sex, eGFR, and immunosuppressive therapy. In comparison to RTR with osteoporosis, those with normal BMD were less likely to have high-AAC (OR 0.23, 95% CI 0.08-0.65; P=0.01). Conclusion Reduced BMD is highly prevalent in RTR. The inverse association between BMD and vascular calcification may support the existence of a bone-vascular axis, and may provide insights into an overlooked and substantially prevalent modifiable cardiovascular risk factor after renal transplantation.