LymeNet Flash: Low Anion Gap

This is topic Low Anion Gap in forum Medical Questions at LymeNet Flash.

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Posted by abigail (Member # 14936) on :

I am trying to save myself some research. Anybody know a low anion gap is all about? Thanks.

Posted by SandiB (Member # 1557) on :

Anion gap

To achieve electrochemical balance, ionic elements in the extracellular fluid must equal a net charge of zero. Therefore, the number of negatively charged ions (anions) should equal the number of positively charged ions (cations). Measured serum anions are chloride and bicarbonate, and the unmeasured anions include phosphates, sulfates, and proteins (eg, albumin). The primary measured serum cation is sodium, but other cations exist, such as calcium, potassium, and magnesium. Under typical conditions, unmeasured anions exceed unmeasured cations; this is referred to as the anion gap and can be represented by the following formulas:

(Chloride + Bicarbonate) + Unmeasured Anions = Sodium + Unmeasured Cations

Unmeasured Anions - Unmeasured Cations = Sodium - (Chloride + Bicarbonate)

Anion Gap = (Sodium) - (Chloride + Bicarbonate)

Practically, a metabolic acidosis is divided into processes that are associated with a normal anion gap (8-12 mEq/L) or an elevated anion gap (>12 mEq/L). A normal anion gap metabolic acidosis involves no gain of unmeasured anions; however, because of the need for electrical neutrality, serum chloride replaces the depleted bicarbonate, and hyperchloremia develops. In contrast, an elevated anion gap metabolic acidosis is caused when extra unmeasured anions are added to the blood.
SandiB