A tale of two homocysteines -: and two hemodialysis units

Pharmacologic doses of folic acid are commonly used to reduce the hyperhomocysteinemia of end-stage renal disease (ESRD). Vitamin Bla acts at the same metabolic locus as folic acid, but information is lacking about the specific effects of high doses of this vitamin on homocysteine levels in renal failure. We therefore compared the plasma homocysteine concentrations of maintenance hemodialysis patients in two McGill University-affiliate urban tertiary-care medical centers that differed in the use of vitamin Bla and folic acid therapy. Patients in the first hemodialysis unit are routinely prescribed high-dose folic acid (HI-F, 6 mg/d), whereas those in the second unit receive high-dose vitamin B-12 in the form of a monthly 1-mg intravenous injection, along with conventional oral folic acid (HI-B-12, 1 mg/d). Predialysis homocysteine was 23.4 +/- 6.8 mu mol/L (mean +/- SD) in the HI-F unit and 18.2 +/- 6.1 mu mol/L in the HI-B-12 unit (P < .002), Postdialysis homocysteine was 14.5 +/- 4.1 in the HI-F unit and 10.6 +/- 3.4 mu mol/L in the HI-B-12 unit (P = ,0001). Multiple regression analysis indicated that high-dose parenteral vitamin B-12 was associated with a lower homocysteine concentration even after controlling for the potential confounders of sex, serum urea, serum creatinine, urea reduction ratio, and plasma cysteine. Because this was a cross-sectional observational study, we cannot exclude the possibility that unidentified factors, rather than the different vitamin therapies, account for the different homocysteine levels in the two units. Careful prospective studies of the homocysteine-lowering effect of high-dose parenteral vitamin B-12 in ESRD should be undertaken. Copyright (C) 2000 by W.B, Saunders Company.