Although hyperkalemia can be a serious disorder associated with serious consequences, the inattention to, or inappropriate treatment of, factitious hyperkalemia can result in its own set of unnecessary and potentially dangerous interventions. One should suspect factitious hyperkalemia when the patient lacks kidney disease and does not show the typical signs and symptoms of muscle weakness or electrocardiographic abnormalities associated with true hyperkalemia. If suspicious, the clinician should obtain a more accurate specimen or account for leukocytosis, thrombocytosis, or genetic factors when weighing the importance of the measured value. Secondary, nonrenal causes of hyperkalemia should also be considered since the disruption may be iatrogenic or a result of an equally serious underlying disorder.

Factitious hyperkalemia, or pseudohyperkalemia, reflects an artificially high measured potassium level resulting from its release just before or after phlebotomy. Venous stasis from a tourniquet, fist clenching, straining, or hyperventilating can cause a potassium efflux from cells. Specimens obtained using a small-gauge needle, stored on ice, or processed after a considerable delay may also cause falsely elevated potassium results. In vitro potassium will be released from clots of white blood cells and platelets once the blood has been drawn and will be exacerbated by significant cases of leukocytosis (>100 × 10⁹/L) or thrombocytosis (>1,000 × 10⁹/L) commonly found in myeloproliferative disorders or Kawasaki syndrome. Finally, familial pseudohyperkalemia, a genetic condition passed as an autosomal dominant trait on chromosome 16 may predispose affected patients to factitious hyperkalemia as a result of an abnormal leakage of ions across the red blood cell membranes. Any combination of these factors may raise the measured potassium level by 2 mEq/L; the practitioner should consider how the specimen was processed while examining the patient for symptoms. Important diagnostic studies include measures of renal function tests, an electrocardiogram, and a repeat specimen. If the repeat level is normal, the practitioner should be reassured; however, if the potassium remains persistently elevated, further investigation and treatment may be warranted.