Turnover of57Co‐labelled Vitamin B12‐Transcobalamin II and Autologous131I‐labelled IgG in a Patient with Antibody to Transcobalamin II

In a pernicious anaemia patient with a circulating antibody to transcobalamin II (TC II), the plasma clearance of radioactive vitamin B12bound to TC II has been shown to be much slower (plasma half‐life 8.2 days) than in control subjects (plasma half‐life 0.7 days). Thus, the patient's high serum vitamin B12binding capacity and elevated serum vitamin B12are the result of decreased catabolism of TC II due to the presence of antibody. The turnover of the B12‐TC II‐antibody complex was shorter than that observed for autologous131I‐labelled IgG (plasma half‐life 16.8 days). This difference is most likely due to dissociation of the complex.