Nonradioactive vitamin B12 absorption test evaluated in controls and in patients with inherited malabsorption of vitamin B12.
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.
Bor
Mustafa Vakur
MV
Department of Clinical Biochemistry, NBG, AS, Aalborg Hospital, Aarhus University Hospital, Denmark. vakurbor@hotmail.com
Cetin
Mualla
M
Aytaç
Selin
S
Altay
Cigdem
C
Nexo
Ebba
E
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*
D014155:Transcobalamins; D007437:Intrinsic Factor; D014805:Vitamin B 12