Evaluation of Elevated Vitamin B12 Levels

Initial Assessment and Laboratory Workup

The National Comprehensive Cancer Network recommends a focused history and physical examination to identify underlying myeloproliferative disorders, hematologic malignancies, or solid organ diseases in patients with elevated vitamin B12 levels 1, 2
A complete blood count with differential and peripheral smear review should be performed to look for eosinophilia, monocytosis, dysplasia, circulating blasts, or other cytopenias, with assessment of mean corpuscular volume (MCV) and red cell distribution width (RDW) 1, 2, 3, 4
A comprehensive metabolic panel, including liver function tests, renal function, lactate dehydrogenase (LDH), and uric acid, should be obtained to evaluate for hepatic dysfunction, renal impairment, and hematologic malignancies 1, 2, 4, 5
Serum tryptase level should be measured, as elevated tryptase alongside elevated B12 strongly suggests myeloproliferative variant, particularly PDGFRA fusion gene-associated neoplasms or systemic mastocytosis 1, 2
C-reactive protein (CRP) should be measured to help distinguish inflammatory conditions and assess disease activity 1, 2, 3

If CBC shows eosinophilia (>1,500/μL), bone marrow aspirate and biopsy with immunohistochemistry, conventional cytogenetics, and FISH and/or nested RT-PCR to detect tyrosine kinase (TK) fusion gene rearrangements should be performed 1, 2
Next-generation sequencing (NGS) via myeloid mutation panels may be useful when no TK fusion genes are detected 1, 2
If hepatic dysfunction is present, consider hepatic imaging and assess for cirrhosis, hepatocellular carcinoma, or metastatic disease 2
If renal dysfunction is present, elevated B12 can occur with renal impairment but is typically a marker of poor prognosis 5

Elevated B12 WITH eosinophilia suggests high suspicion for myeloid/lymphoid neoplasm with TK fusion genes or systemic mastocytosis, and bone marrow evaluation should be performed 1, 2
Elevated B12 WITHOUT eosinophilia may be associated with solid organ malignancy, hepatic dysfunction, renal failure, myelodysplastic syndrome, or recent B12 supplementation 1, 2, 5
Elevated B12 >1,000 pg/mL is an independent predictor of in-hospital mortality, with an adjusted odds ratio of 2.20 for in-hospital death (95% CI 1.56-3.08) 5