Universitätsklinikum des Saarlandes, Klinische Chemie und Laboratoriumsmedizin/Zentrallabor, Homburg/Saar.
Dtsch Arztebl Int. 2008 Oct;105(40):680-5. doi: 10.3238/arztebl.2008.0680. Epub 2008 Oct 3.
Vitamin B(12) deficiency is widespread. Among the population groups at risk are older people, vegetarians, pregnant women, and patients with renal or intestinal diseases. The neurological symptoms of vitamin B(12) deficiency are unspecific and can be irreversible. Early detection is therefore important, using the most sensitive and specific markers available.
Selective literature review.
Total serum vitamin B(12) is a late, relatively insensitive and unspecific biomarker of deficiency. Holotranscobalamin (holoTC), also known as active B(12), is the earliest laboratory parameter for B(12) deficiency, while methyl malonic acid (MMA) is a functional B(12) marker that will increase when the B(12) stores are depleted. Isolated lowering of holoTC shows B(12) depletion (negative B(12) balance), while lowered holoTC plus elevated MMA and homocysteine indicates a metabolically manifest B(12) deficiency, although there still may be no clinical symptoms. The diagnostic use of holoTC allows treatment to be instituted before irreversible neurological damage occurs. As the first clinical manifestations of vitamin B(12) deficiency are unspecific, those at risk should have their B(12) status checked regularly, every two to three years. Because no randomized controlled trials have yet been completed, the diagnostic and therapeutic measures proposed here are merely recommendations.
维生素 B(12) 缺乏症较为普遍。高危人群包括老年人、素食者、孕妇以及患有肾脏或肠道疾病的患者。维生素 B(12) 缺乏症的神经学症状无特异性，且可能无法逆转。因此，使用最敏感和最特异的标志物进行早期检测非常重要。
选择性文献回顾。
血清总维生素 B(12)是一种晚期标志物，相对不敏感且特异性低。同型钴胺素（holoTC），也称为活性 B(12)，是 B(12) 缺乏的最早实验室参数，而甲基丙二酸（MMA）是一种功能性 B(12)标志物，当 B(12) 储存耗尽时会增加。单独降低 holoTC 表明 B(12) 耗竭（负 B(12)平衡），而降低的 holoTC 加上升高的 MMA 和同型半胱氨酸表明存在代谢性 B(12)缺乏症，尽管可能仍没有临床症状。holoTC 的诊断用途可使患者在发生不可逆神经损伤之前开始治疗。由于维生素 B(12) 缺乏症的最初临床表现无特异性，因此高危人群应定期（每 2-3 年）检查其 B(12) 状况。由于尚未完成随机对照试验，因此这里提出的诊断和治疗措施仅为建议。
