A Bicarbonate test is an arterial blood gas test, which means that it measures the level of the gas in the bloodstream. Bicarbonate (HCO? ?) is a negatively charged electrolyte present in the blood, which helps to maintain the acid-base balance of the blood. It is usually performed as part of an electrolyte panel (sodium, potassium and chloride) or acid-base imbalance, as well as to monitor conditions that cause the imbalance.