Relationship between methylmalonic acid and cobalamin in uremia

Background. To evaluate the requirement for routine supplementation with vi tamin B-12 and to study the effect of a change from injection to oral B-12 supplementation, we examined the relationship between cobalamin and methylm alonic acid in plasma from 67 patients on chronic hemodialysis, all in regu lar therapy with intramuscular cobalamin injections (1 mg) every third mont h. Methods. Starting just before one cobalamin injection, blood samples were c ollected once a month during a nine-month withdrawal from regular cobalamin substitution to a final three-month period with cyanocobalamin tablets (1 mg) administered once daily. Results. Plasma cobalamin was above the lower reference limit in all subjec ts, and from a peak value one month after the regular injection, the cobala min concentration during the withdrawal period decreased to a level below t he point of origin, followed by a significant rise after cyanocobalamin tab lets. The methylmalonic acid concentrations were above the reference interv al. In the withdrawal period, the concentrations significantly increased fu rther, followed by a significant decrease after oral cyanocobalamin substit ution. Conclusion. We demonstrated a within-patient inverse relationship between t he concentrations of methylmalonic acid and cobalamin in plasma from these uremic patients. Despite the fact that only two of the patients developed s ubnormal plasma cobalamin values, we demonstrated a B-12 depletion during t he withdrawal period. Treatment with cyanocobalamin tablets once daily was found efficient, but the oral doses should possibly be increased.