The first reason is the excessive intake or administration of potassium, which can lead to hyperkalemia. For example, consuming foods that are very rich in potassium, or intravenously infusing solutions containing potassium. Additionally, the use of potassium salts of penicillin can also cause hyperkalemia, as well as the transfusion of stored blood, which can easily lead to hyperkalemia.

Besides excessive intake and administration of potassium, diseases related to reduced excretion can also cause hyperkalemia, such as the most common instances during acute or chronic renal failure, where patients are prone to hyperkalemia.

Furthermore, patients with reduced adrenal cortex function, such as aldosterone deficiency or Addison's disease, are also prone to hyperkalemia. Additionally, the use of diuretics that inhibit potassium excretion, notably spironolactone—a potassium-sparing diuretic—can also cause an increase in blood potassium levels.

Another reason is a change in potassium distribution, such as when potassium moves from inside the cells to the outside, which can easily lead to hyperkalemia. This is common in cases of tissue damage, such as muscle contusion, or electrical burns, and tissue hypoxia, which also can easily lead to a change in potassium distribution, causing an increase in extracellular potassium.

If hemolysis occurs in a test tube, such as if the venipuncture takes too long, or in conditions like leukocytosis or severe shaking of the blood sample, these might also lead to hyperkalemia.

(The use of medications should be under the guidance of a doctor.)