Bor Mustafa Vakur, Cetin Mualla, Aytaç Selin, Altay Cigdem, Nexo Ebba
Department of Clinical Biochemistry, NBG, AS, Aalborg Hospital, Aarhus University Hospital, Denmark.
Clin Chem. 2005 Nov;51(11):2151-5. doi: 10.1373/clinchem.2005.055509. Epub 2005 Sep 15.
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.
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).
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)%.
Measurement of holo-TC after administration of vitamin B(12) is a promising approach for evaluating vitamin B(12) absorption.
目前用于评估维生素B12吸收的检测方法存在问题，因为它们涉及使用放射性标记的维生素B12。我们描述了一种可避免此问题的维生素B12吸收检测方法。
我们在每隔6小时口服三次9微克剂量的维生素B12后24小时，测量钴胺素或钴胺素饱和的转钴胺素（全转钴胺素，holo-TC）。我们研究了17例因Imerslund-Grasbeck综合征（n = 13）或内因子缺乏（n = 4）导致遗传性维生素B12吸收不良的患者、他们必然为杂合子的生物学父母（n = 19）以及健康对照者（n = 44）。
在患者中，维生素B12负荷后全转钴胺素的中位数（范围）变化不显著[1（-42至5）pmol/L]，钴胺素的变化也不显著[-3（-32至22）pmol/L]，这与缺乏可测量的主动或被动吸收一致。然而，在对照者中，全转钴胺素和钴胺素的中位数（范围）增加分别为26（-6至63）pmol/L和41（-37至109）pmol/L。同样，父母的增加量分别为23（-2至47）pmol/L和27（-15至94）pmol/L。全转钴胺素的ROC曲线下平均面积（95%置信区间）为0.97（0.93 - 1.0），钴胺素为0.87（0.79 - 0.94），可区分患者与对照者。全转钴胺素的截断值为6 pmol/L时，诊断敏感性（95%置信区间）为100（81 - 100）%，诊断特异性为92（82 - 97）%。
给予维生素B12后测量全转钴胺素是评估维生素B12吸收的一种有前景的方法。
