Too many bananas
Hyperkalemia is a result of potassium excess. It can be result of aldosterone deficiency causing potassium retention (too little excretion in the kidneys) (1p435). Also possible trauma that damages cells could cause released potassium to overload kidneys (1p435).
1. Nowak TJ, Handford AG. Pathophysiology: Concepts and Applications for Health Professionals. New York: McGraw-Hill, 2004.