Presence of macroproteins on the measurement of vitamin B12: studying high vitamin B12 levels using polyethylene glycol and heterophile antibody blocking tubes

Immune methods are measurement systems that can be affected by interference. The interfering substance may be endogenous immunoglobulins, antibodies, analyte-antibody complexes, and heterophile antibodies. In our study, we aimed to investigate the effect of macrovitamin B12 on high vitamin B12 levels measured using immune methods. Among the serum samples studied in our laboratory; serum from 145 individuals was determined as the patient group and serum from 50 individuals was determined as the control group. We investigated the effect of macroprotein on B12 measurement by using polyethylene glycol (PEG) precipitation, heterophile antibody blocking tube (HBT) and serial dilution methods. According to the recovery evaluation and the modified reference range evaluation after precipitation with PEG, the macrovitamin B12 percentage in the patient group was 58 (40%) and 65 (44.8%), respectively. There was no decrease in vitamin B12 values after the study with HBT. A lack of linearity was observed in 23 (18.7%) of 123 sera with serial dilution method. Macrovitamin B12 should be considered as a differential diagnosis of unexpectedly high vitamin B12 levels. According to the results of our study, we think that it would be appropriate to precipitate with PEG first when there is a suspicion of macrovitamin B12. In collaboration with clinical and laboratory, we recommend that the patient's clinical status and additional laboratory findings be examined, and the patient's sample should be evaluated and interpreted by a specialist in biochemistry by selecting the appropriate interference detection method.