Mineral that serves as an electrolyte and is involved in the balance of fluid within the body. Our bodies contain more than twice as much potassium as sodium (typically nine ounces versus four ounces). About 98 percent of total body potassium is inside our cells. The principal cation (positive ion) of the fluid within cells. It is important in controlling the activity of the heart, muscles, nervous system and just about every cell in the body. Also regulates the water balance and acid-base balance in the blood and tissues. Evidence is showing that potassium is also involved in bone calcification. Potassium is a co-factor in many reactions, especially those involving energy production and muscle building. Increase in serum potassium is seen in states characterized by excess destruction of cells, with redistribution of K+ from the intra- to the extracellular compartment, as in massive hemolysis, crush injuries, hyperkinetic activity, and malignant hyperpyrexia. Decreased renal K+ excretion is seen in acute renal failure, some cases of chronic renal failure, Addison's disease, and other sodium-depleted states. Hyperkalemia due to pure excess of K+ intake is usually iatrogenic. Drugs causing hyperkalemia include amiloride, aminocaproic acid, antineoplastic agents, epinephrine, heparin, histamine, indomethacin, isoniazid, lithium, mannitol, methicillin, potassium salts of penicillin, phenformin, propranolol, salt substitutes, spironolactone, succinylcholine, tetracycline, triamterene, and tromethamine. Spurious hyperkalemia can be seen when a patient exercises his/her arm with the tourniquet in place prior to venipuncture. Hemolysis and marked thrombocytosis may cause false elevations of serum K+ as well. Failure to promptly separate serum from cells in a clot tube is a notorious source of falsely elevated potassium. Decrease in serum potassium is seen usually in states characterized by excess K+ loss, such as in vomiting, diarrhea, villous adenoma of the colorectum, certain renal tubular defects, hypercorticoidism, etc. Redistribution hypokalemia is seen in glucose/insulin therapy, alkalosis (where serum K+ is lost into cells and into urine), and familial periodic paralysis. Drugs causing hypokalemia include amphotericin, carbenicillin, carbenoxolone, corticosteroids, diuretics, licorice, salicylates, and ticarcillin