Folic acid and pyridoxal-5′-phosphate losses during high-efficiency hemodialysis in patients without hydrosoluble vitamin supplementation

Abstract

Objectives: To determine the serum status in folate, pyridoxal-5′-phosphate (the active moiety of pyridoxine), cobalamin, and total homocysteine of chronic dialysis patients not routinely supplemented with B-complex vitamins and to evaluate induced intradialytic losses during high-efficiency hemodialysis. Design: A cross-sectional study. Setting: A university medical center providing tertiary care. Patients: Thirty-six chronic dialysis patients (23 men and 13 women, mean age 57 ± 13 years) treated since 3.8 ± 2.2 years by hemodialysis and not supplemented with hydrosoluble vitamins. Methods: Thrice-weekly hemodialysis was performed using CT-190G (Baxter, IL) or F-20 (Hospal, St-Leonard, Canada) reused dialyzers with a mean blood flow rate of 371 ± 40 mL/min, a dialysate flow rate of 500 mL/min, and a mean session time of 3.7 ± 0.4 hours. Prehemodialysis serum vitamin B 12 and homocysteine, and predialysis and postdialysis serum folate, pyridoxal-5′-phosphate, and urea were measured. Blood-side folate and pyridoxal-5′-phosphate clearances were calculated. Results: Predialysis serum total homocysteine was above normal in all patients, with values ranging from 14.4 to 158.0 μmol/L (mean 40.2 ± 29.6 μmol/L, median 33.5 μmol/L). Whereas the majority, 21 patients, had evidence of coronary, cerebrovascular, and/or peripheral vascular diseases, there was no difference in total homocysteine in patients with or without vascular disease (respectively, 40.8 ± 37.0 μmol/L v 39.4 ± 15.1 μmol/L, P = NS). Predialysis serum concentrations of pyridoxal-5′-phosphate were reduced in 20 patients (56%) and were in the lower normal range for 14 patients. Predialysis and postdialysis serum folate concentrations were 12.4 ± 6.1 nmol/L and 8.6 ± 3.6 nmol/L, whereas predialysis and postdialysis serum pyridoxal-5′-phosphate concentrations were 11.1 ± 7.5 nmol/L and 8.0 ± 5.9 nmol/L. Percent reduction ratios were 68.4% ± 6.6% for urea, 26.3% ± 16.0% for folates, and 27.9% ± 14.2% for pyridoxal-5′-phosphate. Blood-side clearances reached 134.7 ± 22.2 mL/min for folates and 54.4 ± 38.2 mL/min for pyridoxal-5′-phosphate. There was no significant difference in predialysis serum folate and pyridoxal-5′-phosphate in patients with or without evidence of vascular disease. Conclusion: This study confirms that: (1) total serum homocysteine levels are very high in chronic hemodialysis patients not supplemented with B-complex vitamins; (2) folate is significantly cleared or lost during high-efficiency hemodialysis; and (3) pyridoxal-5′-phosphate, the active moiety of pyridoxine, is depleted in most chronic hemodialysis patients without supplementation and that high-efficiency hemodialysis contributes to its depletion.