An anion gap, or serum anion gap, is a test that measures electrically charged particles in a person's blood to discover acid-base imbalances, according to the University of Rochester Medical Center. The anion gap is calculated from the results of an electrolyte panel, which is a separate blood test.
The test can help a physician diagnose acidosis, which occurs when a person's blood is too acidic, and alkalosis, which occurs when a person's blood is not acidic enough, explains the University of Rochester Medical Center. Acidosis can be life-threatening, so it is especially important to diagnose the condition and treat the cause.
A physician might order an anion gap if a person has symptoms of metabolic acidosis, which include fatigue, shortness of breath, nausea and vomiting, low blood pressure and a rapid heart rate. Metabolic acidosis can be caused when a person's body produces too much acid, such as in lactic acidosis or diabetic ketoacidosis, notes the University of Rochester Medical Center.
Another cause of metabolic acidosis occurs when a person loses too much bicarbonate, possibly through diarrhea. It can also occur when a person does not excrete enough acid through urine due to kidney problems, states the University of Rochester Medical Center.