II. Definition

  1. Difference between calculated serum anions and cations

III. Calculation: Anion Gap

  1. AG = Serum Sodium - Serum Chloride - Serum Bicarbonate
  2. AG = uAnions - uCations
    1. Where uAnions = Unmeasured anions (e.g. Albumin, sulfate, phosphate, organic)
    2. Where uCations = Unmeasured cations (e.g. Potassium, calcium, Magnesium, gamma globulins)

IV. Calculation: Corrected Anion Gap (severe hypoalbuminemia)

  1. Corrected Anion Gap indicated when Serum Albumin is very low
  2. AGcorr = AGact + 2.5 * (AlbNl - AlbAct)
    1. Where AGcorr is Anion Gap corrected
    2. Where AGact is the measured, actual Anion Gap
    3. Where AlbNl is the normal albumin
    4. Where AlbAct is the measured, actual albumin

V. Interpretation

  1. Normal Anion Gap: 12 +/- 2 meq/L

VI. Causes: Low Anion Gap

  1. Paraproteinemia (Multiple Myeloma)
  2. Spurious Hyperchloremia (Bromide toxicity)
  3. Hyponatremia
  4. Hypermagnesemia
  5. Hypoalbuminemia
    1. See Corrected Anion Gap above
    2. Anion Gap decreases 2.5 meq per 1 g/dl Albumin drop

VII. Causes: High Anion Gap

  1. Metabolic Acidosis with high Anion Gap (without increased Serum Chloride)
  2. Severe alkalemia (albumin become negatively charged)

VIII. References

  1. Killu and Sarani (2016) Fundamental Critical Care Support, p. 93-114
  2. Bakerman (1984) ABCs of Lab Data, ILD, Greenville, NC
  3. Ghosh (2000) Fed Pract p. 23-33

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Related Studies

Ontology: Anion Gap (C0003074)

Concepts Clinical Attribute (T201)
MSH D000136
SnomedCT 102637000
LNC LP30809-5, MTHU015314
English Anion Gaps, Gap, Anion, Gaps, Anion, Anion gap, function, anion gap, AG - Anion gap, Anion gap, Anion gap, function (observable entity), Anion gap (function), Anion Gap
Portuguese Gap Aniônico
Spanish Anión Gap, anión gap, anion gap, anión restante, brecha aniónica (entidad observable), brecha aniónica (función), brecha aniónica, hiato aniónico, intervalo aniónico
French Trou anionique
German Anionen-Lücke
Italian Gap anionico
Czech AG, anion gap, aniontová mezera
Norwegian Anion gap
Dutch Anion gap