The Frequency of Routine Blood Sampling and Patient Outcomes Among Maintenance Hemodialysis Recipients

RATIONALE & OBJECTIVE: Surveillance blood work is routinely performed in maintenance hemodialysis (HD) recipients. Although more frequent blood testing may confer better outcomes, there is little evidence to support any particular monitoring interval. STUDY DESIGN: Retrospective population-based cohort study. SETTING & PARTICIPANTS: All prevalent HD recipients in Ontario, Canada, as of April 1, 2011, and a cohort of incident patients commencing maintenance HD in Ontario, Canada, between April 1, 2011, and March 31, 2016. EXPOSURE: Frequency of surveillance blood work, monthly versus every 6 weeks. OUTCOMES: The primary outcome was all-cause mortality. Secondary outcomes were major adverse cardiovascular events, all-cause hospitalization, and episodes of hyperkalemia. ANALYTICAL APPROACH: Cox proportional hazards with adjustment for demographic and clinical characteristics was used to evaluate the association between blood testing frequency and all-cause mortality. Secondary outcomes were evaluated using the Andersen-Gill extension of the Cox model to allow for potential recurrent events. RESULTS: 7,454 prevalent patients received care at 17 HD programs with monthly blood sampling protocols (n=5,335 patients) and at 8 programs with blood sampling every 6 weeks (n=2,119 patients). More frequent monitoring was not associated with a lower risk for all-cause mortality compared to blood sampling every 6 weeks (adjusted HR, 1.16; 95% CI, 0.99-1.38). Monthly monitoring was not associated with a lower risk for any of the secondary outcomes. Results were consistent among incident HD recipients. LIMITATIONS: Unmeasured confounding; limited data for center practices unrelated to blood sampling frequency; no information on frequency of unscheduled blood work performed outside the prescribed sampling interval. CONCLUSIONS: Monthly routine blood testing in HD recipients was not associated with a lower risk for death, cardiovascular events, or hospitalizations as compared with testing every 6 weeks. Given the health resource implications, the frequency of routine blood sampling in HD recipients deserves careful reassessment.