Challenges in the diagnosis of hypervitaminemia B12. Interference by immunocomplexes

Background-Aim: High vitamin B12 concentrations are considered a common finding in clinical practice. Thanks to immunoassay accessibility, vitamin B12 has become a usual test in routine health checkups. However, these analytical methods usually present antibody-mediated interferences. Our aim was to propose an algorithm for the screening of antibody-mediated analytical interferences on vitamin B12 immunoassays on the Alinity platform. Methods: Observational, prospective, case-control study was performed during 12 months. Individuals with persistently elevated cobalamin concentrations [>554 pmol/L] were considered as cases in the absence of supplementation or other justifying cause. Individuals under treatment with vitamin B12, or in the context of alcoholism were included as controls. A thorough interference study by macromolecules in immunoassays was performed in serum samples: PEG precipitation, rheumatoid factor, heterophile antibodies and gel permeation chromatography (GPC). Albumin, total B12, IgG and IgM were measured in every GPC collected fraction and chromatograms were drafted. Results: Up to 45% of cases presented interference by B12-immunocomplexes and the precipitation for all of them was >50%. The individual with the lowest interfered vitamin B12 result was 661 pmol/L. Conclusion: The presence of antibody-mediated interferences, mainly B12-immunocomplexes, is a relatively common phenomenon. A simple algorithm for the screening of interferences is useful and reliable in ruling out healthy individuals and highly cost-effective.