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2017/12/08.
概述

维生素B12和叶酸是B族维生素复合体,是正常红细胞形成、组织和细胞修复和DNA合成的必需元素。B12和/或叶酸缺乏反映了其中一种或两者的慢性不足。机体可在肝脏中存储3-5年的B12和几个月的叶酸需要量,成年人叶酸和B12缺乏的相关症状需几年才能显现出来。由于婴儿和儿童没有大量的储备,因此他们的缺乏症状会更快地显现出来。

长期叶酸或B12的缺乏可导致大细胞性贫血,其特点是红细胞生成减少,体积变大,携氧能力降低。由于贫血,病人会感到乏力、头晕、气促。B12缺乏也会导致不同程度的神经损害,引发手和脚的刺痛麻木及从混淆、易怒到严重痴呆的心智改变。

孕妇需要更大量的叶酸供胎儿的生长发育,如果妇女怀孕,前缺乏叶酸,在妊娠期后果会更严重,有可能会导致胎儿早产或神经管缺陷,如脊柱裂

 

Accordion Title
关于维生素B12和叶酸缺乏
  • 症状

    与B12和叶酸缺乏相关的症状经常是轻微的,没有特异性。他们经常与大细胞性贫血、神经和胃肠道改变有关。早期缺乏的患者可能会在出现明显症状之前被诊断。其他患者可能会经历从轻微到严重的一系列症状,包括:

    • 思维混淆
    • 妄想症
    • 腹泻
    • 眩晕
    • 疲劳、乏力
    • 食欲不振
    • 吸收不良
    • 脸色苍白
    • 心率加快
    • 呼吸急促
    • 口舌痛
    • 兴奋、麻木和/或脚、手、胳膊和腿烧灼感(B12缺乏)

     

  • 病因

    B12和叶酸缺乏可能归因于摄取不足、吸收不良、丢失增加或需要增加。多叶的绿色蔬菜、柑橘类水果、干豆、酵母和强化谷物(添加叶酸)中含有叶酸盐,也叫叶酸。动物蛋白如红肉、鱼、家禽、牛奶、蛋和强化谷物中含有B12。摄取不足导致的B12缺乏是不常见的,但可见于完全素食主义者(不吃任何动物制品)及她们母乳喂养的婴儿。

    胃酸分泌不足可导致B12缺乏,它是从摄入的蛋白中分离B12所必需的。这是老年人以及使用抑制胃酸生成的药物的人群B12缺乏的常见原因。B12缺乏也可归因于内因子缺乏。内因子是胃壁细胞产生的一种物质,并与B12结合后,通过肠道吸收。恶性贫血涉及到胃壁细胞的损伤,导致内因子生成减少。

    B12和叶酸缺乏可起因于下列一般性消化不良,例如:乳糜泻—对小麦不耐受而引起炎症或消化不良,细菌在胃肠道的过度生长,或胃、胃壁细胞或肠管的部分切除手术。

    肝病肾病导致的慢性紊乱和酒精中毒可导致B12和叶酸水平降低,药物治疗如苯妥英、二甲双胍(糖尿病的治疗)、或氨甲喋呤(关节炎的治疗)可导致同样的结果。所有怀孕的妇女需要更大量的叶酸来维持胎儿的正常发育。怀孕前的缺乏会在妊娠期加重。

  • 试验

    B12及叶酸缺乏导致的巨幼细胞贫血可以通过常规的全血细胞计数检测到。实验室检查通常是检测是否缺乏,缺乏的严重程度,确定缺乏的根本原因,监测治疗效果。

    实验室检查
    常用于诊断和监测B12和叶酸缺乏的试验:

    • B12:如果低,表明有缺乏,但是不能明确原因。如果正常,依然可能存在叶酸缺乏。也可用来监测治疗效果。
    • 全血细胞计数:是发现血细胞异常的常规检测项目。可以测量细胞的类型、数量和特征。B12和叶酸均缺乏的贫血,血红蛋白的含量会降低,红细胞异常增大(大红细胞或巨幼红细胞),白细胞和血小板减少。
    • 叶酸:血清或红细胞叶酸都可以检测。有人认为红细胞叶酸更具有临床相关性。二者中任意一种水平降低均提示叶酸缺乏。如果正常,仍有可能存在B12缺乏。可用来监测治疗效果。

    偶尔用来诊断B12和叶酸缺乏的试验:

    帮助确定B12缺乏原因的检查:

    • 希林试验:曾经用来确诊恶性贫血。这个试验不再广泛应用。
    • 内因子结合抗体:干扰B12的结合,可以出现在恶性贫血患者。这是一项特殊试验,不常用。
    • 内因子阻滞抗体:它是一种阻滞B12与内因子结合的蛋白质,出现在50%以上的恶性贫血患者。
    • 壁细胞抗体:是一种针对能产生内因子的胃壁细胞的抗体。见于相当高比例的恶性贫血及其他机能紊乱的患者。

     

  • 治疗

    B12和叶酸缺乏的治疗经常包括长期或终生的药物补充疗法。缺乏内因子或患吸收不良的患者需要注射B12。叶酸盐/叶酸是口服添加物。医生推荐所有想要孩子的妇女在怀孕前和妊娠期摄取叶酸添加物以保证具有足够的储备促使胎儿正常发育。

    如果患者B12和叶酸都缺乏,需要二者均加以补充。如果B12缺乏的患者只摄取叶酸制剂,也许会解决大细胞性贫血,但是由B12缺乏导致的潜在的神经病变(神经损害)将会持续存在。正确的治疗会解决症状但可能不会逆转所有的神经损害。

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