title: Elevated plasma vitamin B12 levels as a marker for cancer: a population-based cohort study.
abstract: BACKGROUND
  A substantial proportion of patients referred for plasma vitamin B12 (cobalamin [Cbl]) measurement present with high Cbl levels, which have been reported in patients with different cancer types. However, the cancer risk among patients with newly diagnosed high Cbl levels has not been adequately examined.
  
  
  METHODS
  We conducted this cohort study using population-based Danish medical registries. Patients referred for Cbl measurement with levels greater than the lower reference limit (≥200 pmol/L) were identified from the population of Northern Denmark during the period of 1998 to 2009 using a database of laboratory test results covering the entire population. Data on cancer incidence (follow-up 1998-2010), Cbl treatment, and prior diagnoses were obtained from medical registries. Patients receiving Cbl treatment were excluded. Cancer risks were calculated as standardized incidence ratios (SIRs) with 95% confidence intervals (CIs), stratified by plasma Cbl levels. All statistical tests were two-sided.
  
  
  RESULTS
  We identified 333 667 persons without prevalent cancer and not receiving Cbl treatment. Six percent had Cbl levels greater than the upper reference limit (≥601 pmol/L). Cancer risk increased with higher Cbl levels and was highest during the first year of follow-up (Cbl 601-800 pmol/L: SIR = 3.44, 95% CI = 3.14 to 3.76; Cbl >800 pmol/L: SIR = 6.27, 95% CI = 5.70 to 6.88; both P < .001). The risks were particularly elevated for hematological and smoking- and alcohol-related cancers for persons with high Cbl levels.
  
  
  CONCLUSIONS
  High Cbl levels were associated with the risk of subsequently diagnosed cancer, mostly within the first year of follow-up. This may have clinical implications for the interpretation of high Cbl levels.
authors.affiliation: Affiliations of authors: Department of Clinical Epidemiology (JFBA, LP, HTS) and Department of Clinical Biochemistry (JFBA, EN), Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Johan Frederik Berg
authors.initials: JF
authors.lastname: Arendt
authors.forename: Lars
authors.initials: L
authors.lastname: Pedersen
authors.forename: Ebba
authors.initials: E
authors.lastname: Nexo
authors.forename: Henrik Toft
authors.initials: HT
authors.lastname: Sørensen
mesh_terms: D000328:Adult; D000368:Aged; D014408:Biomarkers, Tumor / Q000097:blood*; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000097:blood* / Q000175:diagnosis / Q000453:epidemiology*; D012042:Registries; D018570:Risk Assessment; D012307:Risk Factors; D013997:Time Factors; D014805:Vitamin B 12 / Q000097:blood*
chemical_list: D014408:Biomarkers, Tumor; D014805:Vitamin B 12