Serum is the part of blood that doesn't contain cells. Sodium, potassium, and chloride levels are usually measured as part of a basic metabolic panel. Electrolyte panel is very useful in assessing acid base balance in a number of medical conditions. Electrolytes affect a person’s body functions in many ways, including the acidity or alkalinity of the blood, the amount of water in the body and various muscle functions. Potassium is found inside the body's cells. Small amounts of it are also found in the blood plasma. It plays an important role in regulating the heart's rhythm and its ability to contract. Sodium is mainly found outside the body cells. It helps in regulating the amount of water in the body.