High potassium values are not uncommon in hospitalized patients, especially in the elderly. One study reported serum potassium levels more than 5 mEq/L in 15% of patients over age 70. However, hyperkalemia is found in relatively few diseases.

Decreased renal potassium excretion. Renal failure is the most common cause of hyperkalemia, both in this category and including all causes of hyperkalemia.

Pseudohyperkalemia. Dehydration can produce apparently high-normal or mildly elevated electrolyte values. Artifactual hemolysis of blood specimens may occur, which results in release of potassium from damaged RBCs, and the laboratory may not always mention that visible hemolysis was present. In one series of patients with hyperkalemia, 20% were found to be due to a hemolyzed specimen, and an additional 9% were eventually thought to be due to some technical error. Rarely, mild hyperkalemia may appear with very marked elevation of platelets.

Exogenous potassium intake. Examples include excessive oral potassium supplements or parenteral therapy that either is intended to supplement potassium (e.g., potassium chloride) or contains medications (e.g., some forms of penicillin) that are supplied as a potassium salt or in a potassium-rich vehicle. Some over-the-countersalt substitutes contain a considerable amount of potassium.

Endogenous potassium sources. Potassium can be liberated from tissue cells in muscle crush injuries, burns, and therapy of various malignancies (including the tumor lysis syndrome), or released from RBCs in severe hemolytic anemias. In some cases where liberated potassium reaches hyperkalemic levels, there may be a superimposed element of decreased renal function.

Endocrinologic syndromes. As noted previously, hyperkalemia may be produced by dehydration in diabetic ketoacidosis. Hyperkalemia is found in about 50% of patients with Addison’s disease. In one series, hyporeninemic hypoaldosteronism was found in 10% of patients with hyperkalemia. Decreased renal excretion of potassium is present in most endocrinologic syndromes associated with hyperkalemia, with the exception of diabetic acidosis.

Drug-induced hyperkalemia. Some medications supply exogenous potassium, as noted previously. A few, including beta-adrenergic blockers such as propranolol and pindolol, digoxin overdose, certain anesthetic agents at risk for the malignant hyperthermia syndrome such as succinylcholine, therapy with or diagnostic infusion of the amino acid arginine, hyperosmotic glucose solution, or insulin, affect potassium shifts between intracellular and extracellular location. In the case of insulin, deficiency rather than excess would predispose toward hyperkalemia. Most other medications that are associated with increase in serum potassium produce decreased renal excretion of potassium. These include certain potassium-sparing diuretics such as spronolactone and triamterene; several nonsteroidal anti-inflammatory agents such as indomethacin and ibuprofen; angiotensin-converting enzyme inhibitors such as captopril; heparin therapy, including low-dose protocols; and cyclosporine immunosuppressant therapy.