A urine potassium assay can be used to determine the cause of reduced serum potassium (hypokalemia). Normally, the kidney will reabsorb more potassium in the presence of hypokalemia. Therefore, a low urine potassium can suggest gastrointestinal potassium loss, poor dietary intake, or a shift of potassium from the extracellular to the intracellular space. On the other hand, a high urine potassium in the face of low serum potassium indicated renal loss, referred to as renal potassium wasting.