Specimen:

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.

See also:
Carbon Dioxide (CO2 Content), Plasma
Chloride, Plasma
Potassium, Plasma
Sodium, Plasma