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.