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Diseases of the adrenal gland
Adrenal glands are small glands located adjacent to the kidneys, and are important in secreting hormones such as cortisol and aldosterone. Aldosterone causes the kidneys to retain sodium and fluid while excreting potassium in the urine. Therefore diseases of the adrenal gland, such as Addison's disease, that lead to decreased aldosterone secretion can decrease kidney excretion of potassium, resulting in body retention of potassium, and hence hyperkalemia.
Potassium can move out of and into cells. Our total body potassium stores are approximately 50 mEq/kg of body weight. At any given time, about 98% of the total potassium in the body is located inside of cells (intracellular), with only 2% located outside of cells (in the blood circulation and in the extracellular tissue). The blood tests for measurement of potassium levels measure only the potassium that is outside of the cells. Therefore, conditions that can cause potassium to move out of the cells into the blood circulation can increase the blood potassium levels even though the total amount of potassium in the body has not changed.
One example of potassium shift causing hyperkalemia is diabetic ketoacidosis. Insulin is vital to patients with type 1 diabetes. Without insulin, patients with type 1 diabetes can develop severely elevated blood glucose levels. Lack of insulin also causes the breakdown of fat cells, with the release of ketones into the blood, turning the blood acidic (hence the term ketoacidosis). The acidosis and high glucose levels in the blood work together to cause fluid and potassium to move out of the cells into the blood circulation. Patients with diabetes often also have diminished kidney capacity to excrete potassium into urine. The combination of potassium shift out of cells and diminished urine potassium excretion causes hyperkalemia.
Another cause of hyperkalemia is tissue destruction, dying cells release potassium into the blood circulation. Examples of tissue destruction causing hyperkalemia include:
- hemolysis (disintegration of red blood cells),
- massive lysis of tumor cells, and
- rhabdomyolysis (a condition involving destruction of muscle cells that is sometimes associated with muscle injury, alcoholism, or drug abuse).