title: Holo-transcobalamin concentration and transcobalamin saturation reflect recent vitamin B12 absorption better than does serum vitamin B12.
abstract: BACKGROUND
  We evaluated whether measurement of vitamin B(12)-saturated transcobalamin (holo-TC) concentrations or TC saturation (holo-TC:total TC) reflects active vitamin B(12) absorption in healthy individuals and patients after vitamin B(12) intake.
  
  
  METHODS
  We obtained blood samples from 31 healthy individuals (age range, 25-57 years) before (days -1 and 0) and after (days 1, 2, and 6) oral administration of three 9-microg doses of vitamin B(12). The blood samples from seven patients (age range, 22-39 years) suspected to have decreased vitamin B(12) absorption were obtained before and 1 day after the vitamin B(12) intake. The blood samples were analyzed for vitamin B(12), total TC, and holo-TC. The TC saturation was calculated.
  
  
  RESULTS
  Intraindividual variation was <13% for all measured values, as calculated from samples removed on day -1 and 0. In healthy individuals (n = 31) after intake of vitamin B(12), the maximum median (range) increase (as percentages and absolute values) was in TC saturation [52 (-2% to 128)% and 0.04 (0-0.23) as a fraction], closely followed by holo-TC concentrations [39 (0-108)% and 34 (0-149) pmol/L]. All but one healthy individual had an increase of >/=15% in these markers. Serum vitamin B(12) showed a smaller increase [14 (-8 to 51)% and 36 (-27 to 290) pmol/L]. After vitamin B(12) intake, three patients with Crohn disease had the lowest increases in holo-TC concentration (3, 7, and 14 pmol/L) and in TC saturation (0.004, 0.01, and 0.01) among patients and 30 healthy individuals.
  
  
  CONCLUSIONS
  Holo-TC concentrations and TC saturation reflect normal vitamin B(12) absorption better than does serum vitamin B(12).
authors.affiliation: Department of Clinical Biochemistry, AKH, Aarhus University Hospital, Norrebrogade 44, DK-8000 Aarhus C, Denmark. vakurbor@hotmail.com
authors.forename: Mustafa Vakur
authors.initials: MV
authors.lastname: Bor
authors.forename: Ebba
authors.initials: E
authors.lastname: Nexø
authors.forename: Anne-Mette
authors.initials: AM
authors.lastname: Hvas
mesh_terms: D000042:Absorption; D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D044967:Serum; D014155:Transcobalamins / Q000032:analysis*; D014805:Vitamin B 12 / Q000008:administration & dosage* / Q000097:blood / Q000378:metabolism*
chemical_list: D014155:Transcobalamins; D014805:Vitamin B 12