Interference by vitamin B12-macrocomplexes: towards an effective detection and correct interpretation of hypo- and hypervitaminemia

Abstract

The presence of macro-B12 is a cause of factual hypervitaminemia B12. Precipitation with polyethylene glycol (PEG) is a simple method of removing high-molecular-weight biomolecules. However, “free” molecule may co-precipitate. This fact imposes the need to establish new reference values for the post-precipitation result. The main aims of the study were to (Baeza I, Corchón A, Pérez JM, Remacha AF, Rocha H, Rodríguez-Portugal E, et al. Basic Aspects of vitamin B12. In: Communication Committee of the Spanish Society of Laboratory Medicine (SEQCML). Clinical significance of vitamin B12 deficiency. Beyond megaloblastic anemia; 2022. ISBN: 978-84-89975-60-6): establish post-PEG reference intervals (RIs) for total vitamin B12 (Iqtidar N, Chaudary MN. Misdiagnosed vitamin B12 deficiency a challenge to be confronted by use of modern screening markers. J Pak Med Assoc 2012;62:1223–9); compare the two bibliographic criteria for defining the presence of macro-B12 (Green R. Vitamin B12 deficiency from the perspective of a practicing hematologist. Blood 2017;129:2603–11); evaluate the joint usefulness of percentage post-PEG vitamin B12 recovery and post-PEG RIs to inform the real vitamin B12 status; and (Carmel R. Diagnosis and management of clinical and subclinical cobalamin deficiencies: why controversies persist in the age of sensitive metabolic testing. Biochimie 2013;95:1047–55), propose interpretative comments for ease of interpretation. Prospective study in which 488 serum samples from “healthy” individuals were included and analyzed to determine recovery and RIs following PEG precipitation. Subsequently, a retrospective analysis was carried out in order to evaluate the joint usefulness of both definitions for a suspicion of macro-B12. A total of 297 cases were included. Recovery and post-PEG RIs determined on an Alinity i platform ranged from 60 to 107 % and from 118 to 506 pmol/L, respectively. McNemar’s test revealed statistically significant differences between both criteria for estimating interference. However, both methodologies showed good agreement. In 27 cases, the presence of macro-B12 coexisted with true hypervitaminemia B12. No case of coexistence of macro-B12 with vitamin B12 deficiency was detected in our series. Laboratory reports should include total vitamin B12 concentration, recovery and post-PEG vitamin B12 concentration with their adjusted RIs to better assess the body vitamin status.