Total and bone-specific alkaline phosphatase are associated with bone mineral density over time in end-stage renal disease patients starting dialysis

BACKGROUND: Alkaline phosphatase (ALP) and bone-specific ALP (BALP) are implicated in the abnormal skeletal mineralization and accelerated vascular calcification in chronic kidney disease (CKD) patients. Whereas ALP and BALP may predict mortality in CKD, BALP is reported to have higher sensitivity and specificity than total ALP in reflecting histological alterations in bone; however, results on their associations with bone mineral density (BMD) are inconsistent. Here we evaluated associations of total ALP and BALP with BMD during up to 24 months in end-stage renal disease (ESRD) patients. METHODS: ) underwent measurements of total ALP and BALP and total and regional body BMD (by dual-energy X-ray absorptiometry) at dialysis initiation (n = 194), and after 12 (n = 98) and 24 months (n = 40) on dialysis. During the study period, serum concentrations of ALP and BALP increased significantly (p < 0.001), whereas total and regional BMD remained stable. BMD correlated inversely with total ALP (rho = -0.20, p = 0.005) and BALP (rho = -0.30, p < 0.001) at baseline, and correlations were similar also at 12 and 24 months. CONCLUSION: ALP and BALP are equally accurate albeit weak predictors of BMD in ESRD patients, both at baseline and longitudinally. The dissociation between stable BMD and increasing ALP and BALP may possibly reflect increased soft tissue calcifications with time on dialysis.