A tale of two homocysteines - and two hemodialysis units

Pharmacologic doses of folic acid are commonly used to reduce the hyperhomo cysteinemia of end-stage renal disease (ESRD). Vitamin Bla acts at the same metabolic locus as folic acid, but information is lacking about the specif ic effects of high doses of this vitamin on homocysteine levels in renal fa ilure. We therefore compared the plasma homocysteine concentrations of main tenance hemodialysis patients in two McGill University-affiliate urban tert iary-care medical centers that differed in the use of vitamin Bla and folic acid therapy. Patients in the first hemodialysis unit are routinely prescr ibed 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 in jection, along with conventional oral folic acid (HI-B-12, 1 mg/d). Predial ysis 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 homo cysteine 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 conc entration even after controlling for the potential confounders of sex, seru m urea, serum creatinine, urea reduction ratio, and plasma cysteine. Becaus e this was a cross-sectional observational study, we cannot exclude the pos sibility that unidentified factors, rather than the different vitamin thera pies, account for the different homocysteine levels in the two units. Caref ul prospective studies of the homocysteine-lowering effect of high-dose par enteral vitamin B-12 in ESRD should be undertaken. Copyright (C) 2000 by W. B, Saunders Company.