Potassium (K+) analysis measures the concentration of this essential cation (positive ion) both inside cells and in blood serum. Potassium is a key element in maintaining the electrical potential of cell membranes, making it necessary for nerve impulse transmission and the contraction of smooth and skeletal muscles, including the heart muscle and its rhythm. Its blood level is very tightly regulated by the kidneys and is influenced by hormones (such as aldosterone) and acid-base balance.