Serum calcium dynamics and risk of all-cause hospitalization and mortality in hemodialysis patients: a landmark analysis from the international DOPPS

Background Calcium is measured repeatedly in hemodialysis care, yet most studies characterize exposure using a single value rather than its temporal behavior. We examined whether recent serum calcium dynamics are associated with short-term hospitalization and mortality in maintenance hemodialysis patients. Methods Using the Dialysis Outcomes and Practice Patterns Study phases IV–VII, we conducted a quarterly dynamic landmark analysis. At each landmark, total calcium values during the preceding 180 days were summarized as the latest value, mean, linear slope, residual standard deviation (rSD), and time-below-range (TBR, <8.6 mg/dL) and time-above-range (TAR, >10.0 mg/dL). All-cause hospitalization and death were assessed over the subsequent 90 days using discrete-time survival models. Results Among 81 475 patients contributing 431 618 landmarks, 68 632 hospitalizations and 12 886 deaths occurred. Latest calcium was not associated with hospitalization (hazard ratio (HR), 1.00) but was associated with higher mortality (HR, 1.16). Lower mean calcium was associated with hospitalization (HR, 0.97), whereas higher mean calcium was associated with death (HR, 1.16). A positive slope and greater rSD were consistently associated with both hospitalization (HRs, 1.10 and 1.15) and death (HRs, 1.38 and 1.37). TBR burden showed graded associations with hospitalization, whereas TAR burden was strongly and dose-dependently associated with mortality. Conclusions Recent calcium dynamics were associated with short-term outcomes in an outcome-specific manner: low calcium and TBR with hospitalization, high calcium and TAR with death, and rising or unstable calcium with both. These findings support longitudinal assessment of serum calcium, particularly its instability, which was not captured by a single value.