The Serum Anion Gap in the Evaluation of Acid-Base Disorders

Abstract

SummaryThe serum anion gap has been utilized to identify errors in the measurement of electrolytes, to detect paraproteins, and, most relevant to the nephrologist, to evaluate patients with suspected acid-base disorders. In regard to the latter purpose, traditionally an increased anion gap is identified when it exceeds the upper limit of normal for a particular clinical laboratory measurement. However, because there is a wide range of normal values (often 8-10 mEq/L), an increase in anion concentration can be present in the absence of an increased anion gap. In addition, the type of retained anion can affect the magnitude of the increase in anion gap relative to change in serum [HCO 3 2 ] being greater with lactic acidosis compared with ketoacidosis. This review examines the methods of calculation of the serum anion gap in textbooks and published literature, the effect of perturbations other than changes in acid-base balance, and its effectiveness in identifying mild and more severe disturbances in acidbase balance. Limitations of the present methods of determining the normal anion gap and change in the anion gap are highlighted. The possibility of identifying the baseline value for individuals to optimize the use of the calculation in the detection of metabolic acidosis is suggested.

Disorders of Acid-Base Balance: New Perspectives

“…In this case, a nonchloride and unmeasured anion is elevated, and for electroneutrality purposes the bicarbonate concentration will decrease. This group of disorders constitutes the anion gap acidosis [1,46] .…”

Pyroglutamic acidosis in association with therapeutic paracetamol use

“…3,14 This effect can be corrected for using the Figge equation to calculate the corrected anion gap: cAG = AG+0.25×(40 -albumin in g/L). [15][16][17] Failure to correct the serum anion gap for hypoalbuminaemia would have led to a significant underappreciation of the anion gap in all of our cases, and in case 3 would have resulted in the incorrect interpretation of a normal anion gap acidosis (rather than concurrent mixed normal and wide gap acidosis). pulmonary emboli), a metabolic alkalosis (likely the result of high-dose bicarbonate supplementation and furosemide therapy) and a wide anion gap metabolic acidosis (pyroglutamic acid).…”

“…In case 4, the high Δ/Δ (ie high ΔAG/ΔHCO 3 ratio) in a metabolic acidosis suggests a concurrent metabolic alkalosis (Table 1 ). 17,18 Conversely, the low Δ/Δ (ie low ΔAG/ΔHCO 3 ratio) in case 3 demonstrates a concurrent hyperchloraemic metabolic acidosis, a likely result of gastrointestinal losses of HCO 3 from chronic diarrhoea.…”

Les utilisations du trou anionique plasmatique corrigé pour le diagnostic de l’acidose métabolique

“…On retrouve alors l'équation suivante [2] : [ ). En effet, la prise en compte de la kaliémie dans le calcul du TAP n'a, a priori, d'intérêt que quand elle est très augmentée, ou très diminuée, car ses variations physiologiques sont minimes et n'ont qu'une influence clinique mineure [3]. Il sera donc judicieux de l'incorporer au TAP pour des concentrations très élevées (> 6 mmol/l), car la différence obtenue pouvant être significative dans le calcul.…”

“…On retrouverait alors une valeur de TAP plutôt à 7 ± 2 mEq/l [6]. Il est important d'insister sur le fait que la norme du TAP est variable selon les centres, du fait d'une dépendance à la technique de dosage utilisée selon l'automate de chaque laboratoire de biochimie [3,7]. Cela a une importance majeure pour la précision du calcul du TAP.…”