Immune complexes and persistent high levels of serum vitamin B 12

Summary Introduction Patients with persistent high levels of serum vitamin B 12 were often referred to Hematology departments. In this study, characteristic of patients with serum vitamin B 12 levels higher than 2500 pmol/L (high B 12) were studied. Methods Prevalence of high B 12 was evaluated during a 10‐month period. Samples with high B 12 were incubated with polyethylene glycol ( PEG ) and a new measurement of vitamin B 12 was carried out using the supernatant. As a pilot study, 26 frozen samples with high B 12 were evaluated for changes in vitamin B 12 after PEG . Moreover, a prospective study was carried out during three consecutive months. Size exclusion chromatography was employed to demonstrate the presence of immune complexes ( IC s) with plasma vitamin B 12‐binding proteins in some serum samples with high B 12. Results Prevalence of high B 12 was 1.3%. Results from 26 frozen samples and from a prospective study (28 cases) showed that undergoing vitamin B 12 treatment was the main cause of high B 12. However, IC s were detected in 10 frozen samples and in seven cases (25%) of the prospective study, respectively. Serum vitamin B 12 decreased to normal values after precipitation with PEG , and size exclusion chromatography confirmed IC s. An association with autoimmune or hematological disorders was observed. Conclusions In patients with repeatedly high B 12 levels, IC s were detected in approximately 25% of samples. Precipitation with PEG is an easy method to confirm the presence of IC s and to evaluate serum vitamin B 12 levels in these patients.