Anion gap is the difference between the measured and unmeasured ions in plasma, explains the American Association for Clinical Chemistry. The test helps diagnose problems with the acid-base balance in the body.
Plasma should have an equal number of positive and negative ions, notes the American Association for Clinical Chemistry. The anion gap test helps determine if there is more of one type of ion than the other. Before calculating anion gap, a doctor or laboratory professional must know an individual's chloride, bicarbonate and sodium levels. The most commonly used equation for determining anion gap as AG = sodium - (chloride + bicarbonate). This calculation represents the number of unmeasured ions present in the blood.
Although anion gap is used to identify disturbances in the acid-base balance of the blood, the test doesn't reveal the underlying cause of the problem, explains the American Association for Clinical Chemistry. Some potential causes of metabolic acidosis include kidney damage, aspirin overdose and uncontrolled diabetes. The anion gap test also helps monitor patients who are being treated for metabolic acidosis.
Human blood is usually kept at a pH level of approximately 7.4, states The Merck Manuals Home Edition. Acidic substances have a pH less than 7.0, while alkaline substances have a pH above 7.0.