A comprehensive metabolic panel is a comprehensive set of 14 different blood tests for chemical levels related to metabolism. It also goes by the name of chemical panel, chem panel and Chem 12. It is generally used by family physicians as part of a normal check-up to establish base levels for metabolic function as trends in levels are generally more important than absolute levels. However, it is routinely used by diagnosticians and emergency room personnel to rule out common metabolic disorders and to check electrolyte levels, kidney function and liver function. The test is usually performed when the patient has not eaten for twelve hours.