Lab
Anion Gap
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Anion Gap
, Corrected Anion Gap
See Also
AcidBase Homeostasis
Metabolic Acidosis
with high Anion Gap
Definition
Difference between calculated serum anions and cations
Calculation
Anion Gap
AG =
Serum Sodium

Serum Chloride
 Serum Bicarbonate
AG = uAnions  uCations
Where uAnions = Unmeasured anions (e.g. Albumin, sulfate, phosphate, organic)
Where uCations = Unmeasured cations (e.g.
Potassium
, calcium,
Magnesium
, gamma globulins)
Calculation
Corrected Anion Gap (severe hypoalbuminemia)
Corrected Anion Gap indicated when
Serum Albumin
is very low
AGcorr = AGact + 2.5 * (AlbNl  AlbAct)
Where AGcorr is Anion Gap corrected
Where AGact is the measured, actual Anion Gap
Where AlbNl is the normal albumin
Where AlbAct is the measured, actual albumin
Interpretation
Normal Anion Gap: 12 +/ 2 meq/L
Causes
Low Anion Gap
Paraproteinemia
(
Multiple Myeloma
)
Spurious
Hyperchloremia
(Bromide toxicity)
Hyponatremia
Hypermagnesemia
Hypoalbuminemia
See Corrected Anion Gap above
Anion Gap decreases 2.5 meq per 1 g/dl Albumin drop
Causes
High Anion Gap
Metabolic Acidosis
with high Anion Gap (without increased
Serum Chloride
)
Severe alkalemia (albumin become negatively charged)
References
Killu and Sarani (2016) Fundamental Critical Care Support, p. 93114
Bakerman (1984) ABCs of Lab Data, ILD, Greenville, NC
Ghosh (2000) Fed Pract p. 2333
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