Anion Gap is automatically performed with the following panel tests: Electrolyte Panel (LYTES), Renal Function Panel (RENAL), Basic Metabolic Panel (BASIC) and/or Comprehensive Panel (COMP). It is not available as an individual test. Anion Gap is a calculated test using the sodium, chloride and CO2 results on serum. The formula for calculating is: Sodium - (Chloride + CO2) = Anion Gap

The primary clinical use of the anion gap is to assess acid-base disturbances in patients, particularly metabolic acidosis. A marked increase in anion gap (>25 mmol/L) is almost always evidence of metabolic acidosis. Increased anion gap results can be caused by renal failure, diabetic ketoacidosis, starvation, lactic acidosis, ethylene glycol intoxication and methanol intoxication. Reduced anion gap results are less common. Low anion gap can be associated with hypoalbuminemia, myeloma, and lithium intoxication. Laboratory error in measurement of any of the three components of the calculation (Sodium, chloride or CO2) can invalidate the anion gap result.