title: Nonradioactive vitamin B12 absorption test evaluated in controls and in patients with inherited malabsorption of vitamin B12.
abstract: BACKGROUND
  Current tests for evaluation of vitamin B(12) absorption are problematic because they involve the use of radioactively labeled vitamin B(12). We describe a vitamin B(12) absorption test that circumvents this problem.
  
  
  METHODS
  We measured cobalamin or transcobalamin saturated with cobalamin (holo-TC) 24 h after three 9-microg doses of vitamin B(12) given orally at 6-h intervals. We studied 17 patients with inherited malabsorption of vitamin B(12) attributable to Imerslund-Grasbeck syndrome (n = 13) or intrinsic factor deficiency (n = 4), their obligate heterozygous biological parents (n = 19), and healthy controls (n = 44).
  
  
  RESULTS
  In the patients, the median (range) change of holo-TC after the B(12) load was not significant [1 (-42 to 5) pmol/L], nor was the change of cobalamin [-3 (-32 to 22) pmol/L], consistent with a lack of measurable active or passive absorption. In controls, however, the median (range) increases of holo-TC and cobalamin were 26 (-6 to 63) pmol/L and 41 (-37 to 109) pmol/L, respectively. Similarly, the parents showed increases of 23 (-2 to 47) pmol/L and 27 (-15 to 94) pmol/L. The mean areas under the ROC curves (95% confidence intervals) were 0.97 (0.93-1.0) for holo-TC and 0.87 (0.79-0.94) for cobalamin, distinguishing patients from controls. At a cutoff of 6 pmol/L for holo-TC, the diagnostic sensitivity (95% confidence interval) was 100 (81-100)%, and the diagnostic specificity was 92 (82-97)%.
  
  
  CONCLUSIONS
  Measurement of holo-TC after administration of vitamin B(12) is a promising approach for evaluating vitamin B(12) absorption.
authors.affiliation: Department of Clinical Biochemistry, NBG, AS, Aalborg Hospital, Aarhus University Hospital, Denmark. vakurbor@hotmail.com
authors.forename: Mustafa Vakur
authors.initials: MV
authors.lastname: Bor
authors.forename: Mualla
authors.initials: M
authors.lastname: Cetin
authors.forename: Selin
authors.initials: S
authors.lastname: Aytaç
authors.forename: Cigdem
authors.initials: C
authors.lastname: Altay
authors.forename: Ebba
authors.initials: E
authors.lastname: Nexo
mesh_terms: D000042:Absorption; D000293:Adolescent; D000328:Adult; D002648:Child; D005260:Female; D006579:Heterozygote; D006801:Humans; D007437:Intrinsic Factor / Q000172:deficiency; D008286:Malabsorption Syndromes / Q000235:genetics* / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D014155:Transcobalamins / Q000032:analysis; D014805:Vitamin B 12 / Q000493:pharmacokinetics*
chemical_list: D014155:Transcobalamins; D007437:Intrinsic Factor; D014805:Vitamin B 12