Carmel R
Department of Medicine, New York Methodist Hospital, Brooklyn 11215, USA.
Annu Rev Med. 2000;51:357-75. doi: 10.1146/annurev.med.51.1.357.
The application of sensitive metabolic tests, such as the deoxyuridine suppression test and measurement of homocysteine and methylmalonic acid, to cobalamin status has identified the entity of mild, preclinical cobalamin deficiency. This state, common in the elderly, responds to cobalamin therapy. Preclinical deficiency may exist within the nervous system as well, although this requires further study. Nevertheless, it is well to remember that not all low cobalamin levels and not all abnormal metabolite results reflect cobalamin deficiency. Interpretation of metabolic results still requires caution, as do proposals to raise the cut-off point for low cobalamin levels to capture some normal levels that are associated with metabolic abnormality. The recognition of mild, preclinical deficiency has opened up many important issues. These include identifying its causes, what should be done about it, and what the clinical impact of the hyperhomocysteinemia itself is. Although malabsorptive disorders, especially food-cobalamin malabsorption, underlie about half of all cases of preclinical deficiency, no cause can be found in the remainder of these cases; poor dietary intake appears to be uncommon. In addition, unusual states of neurologically symptomatic cobalamin deficiency are being recognized, such as nitrous oxide exposure in patients with unrecognized deficiency and severe deficiency in children of mildly deficient mothers. All of these have broadened and complicated the picture of cobalamin deficiency while providing greater opportunities for prevention.
将敏感的代谢检测方法，如脱氧尿苷抑制试验以及同型半胱氨酸和甲基丙二酸的测定，应用于钴胺素状态评估，已识别出轻度、临床前钴胺素缺乏这一情况。这种状态在老年人中很常见，对钴胺素治疗有反应。临床前缺乏也可能存在于神经系统中，不过这还需要进一步研究。然而，要牢记并非所有低钴胺素水平以及并非所有异常代谢产物结果都反映钴胺素缺乏。代谢结果的解读仍需谨慎，提高低钴胺素水平的临界值以涵盖一些与代谢异常相关的正常水平的提议同样如此。对轻度、临床前缺乏的认识引发了许多重要问题。这些问题包括确定其病因、对此应采取什么措施以及高同型半胱氨酸血症本身的临床影响是什么。尽管吸收不良性疾病，尤其是食物钴胺素吸收不良，是约一半临床前缺乏病例的基础，但在其余病例中找不到病因；饮食摄入不足似乎并不常见。此外，正在认识到有神经系统症状的钴胺素缺乏的一些特殊情况，如未被识别出缺乏的患者接触氧化亚氮以及轻度缺乏母亲的孩子出现严重缺乏。所有这些都拓宽并复杂化了钴胺素缺乏的情况，同时也提供了更多预防机会。
