Home parenteral nutrition and vitaminB12 status

The vitamin B12 status of 20 subjects who were on home parenteral nutrition after surgical or functional small bowelresection and were given 1000 μg cyanocobalamin every 3 mo was studied by comparing their plasma vitamin B12, homocysteine (HS), and methylmalonic acid (MMA) concentrations. The plasma vitamin B12 concentration (median 145 pmol/L, 95% confidence interval: 123–217) was subnormal in four cases and borderline in four others. In the “low B12” group, the concentrations of the markers of vitamin B12 deficiency were in the normal range: HS 10.7 μmol/L (8.0–12.3); and MMA, 0.15 μmol/L (0.09–0.19). References values were HS, 10.0 μmol/L (9.4–12.6); and MMA, 0.16 μmol/L (0.10–0.19). Thus, there were no metabolic signs of vitamin B12 deficiency in these subjects on parenteral nutrition, despite the fact that their plasma vitamin B12 levels were low. Analysis of individual data showed that the four patients with low circulating B12 had markers of intracellular vitamin B12 deficiency in the normal range.