Chen Xinke, Remacha Angel F, Sardà M Pilar, Carmel Ralph
Department of Medicine, New York Methodist Hospital, Brooklyn, NY 11215, USA.
Am J Clin Nutr. 2005 Jan;81(1):110-4. doi: 10.1093/ajcn/81.1.110.
Cobalamin attached to transcobalamin II (TC II), known as holo-TC II, is the active cobalamin fraction taken up by tissues. Holo-TC II is also the form in which absorbed cobalamin enters the circulation from the ileum. Therefore, holo-TC II has been proposed variously as a marker of cobalamin adequacy, cobalamin absorption, or both, including even its advocacy as a surrogate Schilling test. Such claims carry conflicting diagnostic implications because metabolic adequacy and absorption are not identical.
The objective was to examine metabolic and absorptive influences on holo-TC II.
Treated patients with pernicious anemia (PA), who have abnormal absorption but a normal metabolic status, were chosen as the model to differentiate between the effects of the 2 cobalamin-related characteristics. Serum holo-TC II and indexes of cobalamin metabolism in 23 treated patients were compared with those of 6 untreated PA patients (abnormal absorption and metabolic status) and 33 control subjects (normal absorption and metabolic status).
Holo-TC II, which correlated directly with cobalamin and inversely with homocysteine, was significantly higher in treated PA patients in metabolic remission than in untreated PA patients (74 +/- 59 compared with 9 +/- 6 pmol/L) and was significantly lower than in control subjects (105 +/- 58 pmol/L), although the latter difference was small and the values overlapped greatly.
Metabolic cobalamin status is a major determinant of serum holo-TC II. Absorption status may have mild influence as well, although other explanations remain possible. Serum holo-TC II cannot be used clinically to diagnose cobalamin malabsorption because of overlap with normal values. The influences on holo-TC II are complex and require careful analysis.
与转钴胺素II（TC II）结合的钴胺素，即全转钴胺素II（holo-TC II），是被组织摄取的活性钴胺素部分。全转钴胺素II也是吸收的钴胺素从回肠进入循环的形式。因此，全转钴胺素II被不同地提议作为钴胺素充足、钴胺素吸收或两者的标志物，甚至有人主张将其作为替代希林试验。这些说法具有相互矛盾的诊断意义，因为代谢充足和吸收并不相同。
目的是研究代谢和吸收对全转钴胺素II的影响。
选择患有恶性贫血（PA）且吸收异常但代谢状态正常的经治疗患者作为模型，以区分这两种与钴胺素相关特征的影响。将23例经治疗患者的血清全转钴胺素II和钴胺素代谢指标与6例未经治疗的PA患者（吸收和代谢状态异常）及33例对照受试者（吸收和代谢状态正常）进行比较。
全转钴胺素II与钴胺素呈正相关，与同型半胱氨酸呈负相关，代谢缓解的经治疗PA患者的全转钴胺素II显著高于未经治疗的PA患者（分别为74±59与9±6 pmol/L），且显著低于对照受试者（105±58 pmol/L），尽管后一差异较小且数值有很大重叠。
钴胺素代谢状态是血清全转钴胺素II的主要决定因素。吸收状态可能也有轻微影响，尽管其他解释仍有可能。由于与正常值重叠，血清全转钴胺素II不能用于临床诊断钴胺素吸收不良。对全转钴胺素II的影响很复杂，需要仔细分析。
