Anion Gap
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Specimen(s):
Plasma
Comments:
The anion gap or electrolyte balance is calculated by the formula Na
- (Cl +HCO3). In normal individuals most of the anion gap is due to
protein. When an unmeasured anion such as ketones, lactate, formate,
or oxalate is present an elevated anion gap results. While the
values for the anion gap are method dependent, there is agreement
that an anion gap > 16 is considered elevated. The reasons for a
decreased anion gap are fewer and include low proteins, multiple
myeloma (tend to be positively charged) and bromide ingestion
(falsely counted as chloride). Patients may have a normal anion gap
and still have acidosis. This is known as hyperchloremic acidosis
where an elevated chloride compensates for the decreased
bicarbonate.