potassium medical definition

A soft, highly or explosively reactive metallic element that occurs in nature only in compounds and is found in or converted to a wide variety of salts used especially in fertilizers and soaps. Its radioisotopes are used in various diagnostic studies, including myocardial scans, detection and localization of tumors, determination of intracellular fluid space, and determination of renal blood flow. Atomic number 19. Also called kalium.