Association of hematocrit value with cardiovascular morbidity and mortality in incident hemodialysis patients

Background. Associations between hematocrit values and clinical outcome have been studied with conflicting results in cardiac patients, end-stage renal disease (ESRD) patients, and ESRD patients with cardiac disease. We studied dialysis patients to determine the relationship between hematocrit value and cardiac risk under current Dialysis Outcomes Quality Initiative (DOQI) practices. Methods. Medicare data were used to study 50,579 incident hemodialysis patients selected from January 1, 1998, to December 31, 1999, who received hemodialysis for 9 months after the onset of ESRD. Patients were divided into groups on the basis of the hematocrit value: less than or equal to30%, > 30% to 33%, less than or equal to33% to less than or equal to36%, > 36% to less than or equal to39%, and > 39%. For hospitalization, the follow-up extended to 2 1/2 years; for mortality, 3 years. Results. Compared to patients with hematocrit values of > 33% to 36%, patients with values of > 36% to 39% and those with values of > 39% had risk ratios for hospitalization due to cardiac disease of 0.92 (95% CI 0.88 to 0.97) and 0.79 (95% CI 0.72 to 0.87), respectively, and risk ratios for death due to cardiac disease of 0.92 (95% CI 0.87 to 0.98) and 0.83 (95% CI 0.74 to 0.93), respectively, in the follow-up period. Conclusion. The significant associations we report do not establish a causal relationship between higher hematocrit values and lower risks of cardiac morbidity and mortality. A randomized clinical trial in low-risk patients is needed to establish causality.