The anion gap (AG) is a mathematical construct that compares the blood sodium concentration with the sum of the chloride and bicarbonate concentrations. It is a helpful calculation that divides the metabolic acidoses into 2 categories: high AG metabolic acidosis (HAGMA) and hyperchloremic metabolic acidosis—and thereby delimits the potential etiologies of the disorder. When the [AG] is compared with changes in the bicarbonate concentration, other occult acid-base disorders can be identified. Furthermore, finding that the AG is very small or negative can suggest several occult clinical disorders or raise the possibility of electrolyte measurement artifacts. In this installment of AJKD’s Core Curriculum in Nephrology, we discuss cases that represent several very common and several rare causes of HAGMA. These case scenarios highlight how the AG can provide vital clues that direct the clinician toward the correct diagnosis. We also show how to calculate and, if necessary, correct the AG for hypoalbuminemia and severe hyperglycemia. Plasma osmolality and osmolal gap calculations are described and when used together with the AG guide appropriate clinical decision making.

阴离子间隙 (AG) 是一种数学结构，用于将血钠浓度与氯化物和碳酸氢盐浓度的总和进行比较。将代谢性酸中毒分为两类：高 AG 代谢性酸中毒 (HAGMA) 和高氯性代谢性酸中毒是一种有用的计算，从而确定了该疾病的潜在病因。当 [AG] 与碳酸氢盐浓度的变化进行比较时，可以识别其他隐匿性酸碱紊乱。此外，发现 AG 非常小或阴性可以提示几种隐匿的临床疾病或增加电解质测量伪影的可能性。在 AJKD 肾脏病学核心课程的这一部分中，我们讨论了代表 HAGMA 的几种非常常见和几种罕见原因的案例。这些病例场景突出了 AG 如何提供重要线索，指导临床医生进行正确诊断。我们还展示了如何计算并在必要时纠正低白蛋白血症和严重高血糖的 AG。描述了血浆渗透压和渗透压间隙计算，并在与 AG 一起使用时指导适当的临床决策。