Parenteral vitamin B12 in macrocytic hemodialysis patients reduced MMA levels but did not change mean red cell volume or hemoglobin

Abstract

Unexplained macrocytic anemia was common in our hemodialysis (HD) unit. Vitamin B12 requirements may be higher in HD patients; therefore, patients may be deficient despite "normal" serum levels. We studied vitamin B12 status and the effect of parenteral vitamin B12 administration in macrocytic HD patients. A normocytic group was included for comparison. Prospective cohort study of 62 HD patients (34 macrocytic, 28 normocytic) from November 2008 to March 2009. Patients were on stable doses of darbepoetin and iron replete. Vitamin B12 1,000 µg IV was given once weekly for 4 weeks and follow-up was 12 weeks. Methylmalonic acid (MMA) level was used as an indicator of vitamin B12 status. MCV and hemoglobin were also examined for an effect of B12 administration. At baseline: all patients had serum B12 levels > 200 pmol/l; 97% had serum folate levels > 55 nmol/l; there was no difference in serum B12 levels between groups (504 vs. 571 pmol/l, p = 0.18); MMA was higher in the macrocytic group (0.56 vs. 0.48 µmol/l, p = 0.048) and hemoglobin (Hg) was lower (119 vs. 125 g/l, p = 0.03); median darbepoetin dose was equivalent (20 µg/week). Following IV vitamin B12, the macrocytic group had a greater and more sustained reduction in MMA (-0.064 vs. -0.0066 µmol/l/wk, p = 0.004). There was no improvement in hemoglobin (Hg), reticulocyte count or MCV in either group. Median darbepoetin dose was unchanged. IV vitamin B12 led to a sustained decline in MMA levels in macrocytic patients, suggesting functional vitamin B12 deficiency at baseline. However, there were no significant changes in Hg or darbepoetin dose.