Objectives
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.
Methods
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.
Results
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.
Conclusions
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.
