Homocysteine, vitamin B12, and serum and erythrocyte folate in peritoneal dialysis and hemodialysis patients

Background: Plasma homocysteine (Hcy) is an independent risk factor for cardiovascular disease. High levels of plasma Hey have been observed in end-stage renal disease patients. Few studies have compared peritoneal dialysis (PD) and hemodialysis (HD) patients and few data are available on erythrocyte folate (ery-F) levels in dialysis patients. Objectives: To evaluate plasma Hey concentrations, vitamin B-12 (B12), and folate status in dialysis patients; to analyze the possible causes of high Hey levels; to follow up changes in folate and B12 concentrations after 6 months. Design: A cross-sectional observational study. Setting: Nephrology division and laboratory of hematology in a university and clinical research hospital. Patients:The study included 82 patients treated with PD for 37 +/- 37 months and 70 patients treated with HD for 136 +/- 95 months. Laboratory Methods: Plasma Hcy was measured by the immunoenzymatic IMx Hey FPIA method (Abbott Laboratories, Diagnostic Division, Abbott Park, IL, U.S.A.), serum folate (s-F) and ery-F by the Stratus folate fluorometric enzyme-linked assay, and B12 by the Stratus Vitamin B-12 fluorometric enzyme-linked assay (DADE-Behring, Newark, DE, U.S.A.). Results: Ninety-six percent of PD and 97% of HD patients had Hey levels above the cutoff(13.5 mu mol/L). Homocysteine level was higher in HD than in PD patients, while the prevalence of hyperhomocysteinemia was similar with the two techniques. Erythrocyte folate was significantly higher in PD (1333 +/- 519 pmol/L) than in HD (1049 +/- 511 pmol/L, p < 0.01). Statistically significant correlations were observed between Hey and B12, s-F, ery-F, and dialysis duration. Multivariate analysis showed a strong correlation between s-F and Hey. After 6 months there were no differences in Hey, B12, s-F, and ery-F levels. Conclusions: Plasma Hey levels were high in more than 95% of our dialysis patients, with no relation to the type of dialysis. Vitamin B-12 and folate were normal in the majority of our patients. However, serum folate was the major determinant of Hcy levels. Such a relation between Hey and folate suggests that levels of folate within the reference interval are inadequate for dialysis patients.