Markedly increased vitamin B12 concentrations attributable to IgG-IgM-vitamin B12 immune complexes.
BACKGROUND
High serum vitamin B12 concentrations have been reported in patients with hepatic disease, disseminated neoplasia, myeloproliferative disorders, and hypereosinophilic syndromes. We recently discovered an extraordinarily increased vitamin B12 concentration in a patient without these underlying conditions.


METHODS
Affinity and size-exclusion chromatography, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and ELISA methods were used to determine the cause of the increased vitamin B12 concentrations in this patient's serum.


RESULTS
The protein G column eluates from 2 apparently healthy volunteers and 2 patients with recent vitamin B12 treatment for anemia had vitamin B12 concentrations of <74 pmol/L, whereas the vitamin B12 concentration in the protein G column eluate from the patient was 7380 pmol/L. The elution profile from size-exclusion chromatography of vitamin B12-binding proteins in the patient's serum revealed an abnormal vitamin-B12-binding protein. SDS-PAGE analysis of the concentrated eluates from the protein G column, under reducing conditions, revealed an additional band with an apparent molecular mass of 76 kDa, which was not present in control column eluates. MALDI-TOF MS identified this band as an IgM heavy chain. By use of a modified ELISA, we determined that the IgM present in the patient's eluates was associated with the IgG to form IgG-IgM immune complexes.


CONCLUSIONS
This case demonstrates the unusual circumstance of a patient with markedly increased vitamin B12 concentrations attributed to immune complexes composed of IgG, IgM, and vitamin B12 and illustrates techniques that can be used to identify this occurrence.
Bowen
Raffick A R
RA
Department of Laboratory Medicine, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, MD 20892-1508, USA.
Drake
Steven K
SK
Vanjani
Rachna
R
Huey
Edward D
ED
Grafman
Jordan
J
Horne
McDonald K
MK
D000690:Amyotrophic Lateral Sclerosis / Q000097:blood* / Q000150:complications / Q000175:diagnosis; D019138:Antibodies, Blocking / Q000097:blood; D000910:Antibodies, Heterophile / Q000097:blood; D000936:Antigen-Antibody Complex / Q000097:blood*; D002845:Chromatography; D019411:Clinical Laboratory Techniques / Q000379:methods; D003704:Dementia / Q000097:blood* / Q000150:complications; D005189:False Positive Reactions; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood* / Q000378:metabolism; D007075:Immunoglobulin M / Q000097:blood* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014805:Vitamin B 12 / Q000097:blood* / Q000276:immunology / Q000378:metabolism
D019138:Antibodies, Blocking; D000910:Antibodies, Heterophile; D000936:Antigen-Antibody Complex; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D014805:Vitamin B 12