Usual values: anion gap = 12+/-4 if potassium is not given, 16+/-4 if it is given.
It is not mandatory to use mmol/l, but all units must be the same. The normals indicated are valid only in mmol/l and in mEq/l.
A high anion gap indicates the presence of indosed anions and therefore, during acidosis, of a metabolic origin.
The corrected anion gap is not valid if albuminemia is not entered. The usual values are identical to the uncorrected anion gap.
A high Plasma Anion Gap reflects the presence of an excess of indosed anions (lactates, phosphates, sulfates, plasma proteins) and therefore metabolic acidosis. However, not all acidosis is accompanied by a change in the Plasma Anion Gap. Thus in human clinical practice, it is customary to distinguish between acidosis without an increase in the Plasma Anion Gap and acidosis with an increase in the Plasma Anion Gap.
Acidosis with normal Plasma Anion Gap (called “hyperchloraemic”, the chloride concentration compensating for the loss of [HCO3−])
digestive loss of bicarbonates
renal tubular acidosis
acidosis by dilution
Acidosis with increased Plasma Anion Gap (called “normochloremic”: an acid increases the concentration of positive ions, which accentuates the Plasma Anion Gap.)
lactic acidosis (which accounts for half of high anion gap acidosis with, however, low sensitivity and specificity)
poisoning: methanol, ethylene glycol, acetylsalicylic acid and MDMA (amphetamines)
Apart from disorders of acid-base balance, the anion gap can be modified in other circumstances. It is thus reduced in hypoalbuminaemia and increased in the opposite case. It may also be slightly increased in inflammatory syndromes.