Bicarbonate is a group of atoms in liquid solution forming the chemical formula HCO3-. Within living organisms, it plays a vital role in balancing the acidity of bodily fluids, most importantly blood. In its pharmaceutical forms (such as sodium bicarbonate), it's used to treat acidosis, but in a person with a normal metabolism, almost 75% of the carbon dioxide in the body is used in the process to create bicarbonate naturally. Testing for bicarbonate concentrations in blood is an important diagnostic indicator of several conditions.
Bicarbonate compounds like calcium bicarbonate are commonly used as over-the-counter antacids.