FC 076DIAGNOSTIC ACCURACY OF BONE TURNOVER MARKERS IN RENAL OSTEODYSTROPHY

Background and Aims A transiliac bone biopsy is the gold standard for diagnosing renal osteodystrophy, but is not recommended as part of routine clinical workup due to its invasive nature. Suitable non-invasive alternatives have yet to be established. The aim of this study was to investigate the diagnostic accuracy novel biochemical markers of bone remodeling compared to that of biointact parathyroid hormone (PTH) for bone turnover as evaluated by histomorphometry. Method Protocolled bone biopsies were performed in end-stage kidney disease patients (ESKD, n = 80) and kidney transplant recipients (n = 119). Full-length (1-84) PTH, bone-specific alkaline phosphatase (BsAP), intact N-terminal propeptide of type I collagen (P1NP), and tartrate-resistant acid phosphatase isoform 5b (TRAP5b) were measured. Diagnostic performance was evaluated by area under the receiver operator characteristics curve (AUC). Optimal diagnostic cutoffs were established in an exploration cohort (n=100), and subsequently validated in a separate subset of patients (n=99). Results Mean age was 55±13 years, two-thirds were men (67%), and 23% had diabetes mellitus. Post-transplant eGFR was 49 [IQR 39, 59] ml/min/1.73m². Bone turnover was low in 47 (24%), normal in 119 (60%), and high in 33 (17%) patients. All biomarkers differed significantly across categories of bone turnover (p < 0.001). The AUC of biointact PTH for high turnover was 0.82 (0.73, 0.91), which was not significantly different from AUC values for BsAP, Intact P1NP, and TRAP5b (0.87, 0.90, and 0.86, respectively). AUC of biointact PTH for low turnover was 0.71 (0.63, 0.78), which was significantly lower than the values for BsAP, Intact P1NP, and TRAP5b (0.79, 0.83, and 0.79, respectively; p < 0.05, all). Calculated optimal diagnostic cutoffs in the exploration cohort are shown in Table 1. Applying these cutoffs in the validation cohort revealed high negative predictive values for both high (92 - 96%) and low (82 - 90%) bone turnover. Positive predictive values were consistently low. Conclusion The diagnostic accuracies of BsAP, Intact P1NP and TRAP5b are sufficient to rule out both high and low bone turnover in CKD. Biointact PTH shows inferior performance, particularly in kidney transplant recipients.