Potassium (body fluid) test is performed to detect chronic kidney conditions and metabolic disorders. This test is performed on a sample of the body fluid of the patient, to measure the levels of potassium present in it. It is also known as Potassium K (body fluid) test. The decrease in extracellular potassium can cause; weakness of the muscles, irritation, increase in the rate of heartbeat, paralysis, etc., whereas, high potassium levels can cause; mental confusion, weakness, numbness, slow heartbeat, etc.