Pseudohyperkalemia in extreme leukocytosis

Spurious elevation of blood K levels is a well known occurrence in patients with extreme leukocytosis. A common explanation is the in vitro release of K from leukocytes undergoing lysis during the clotting process. Since in clinical practice blood electrolytes are now being evaluated in plasma or whole heparinized blood rather than in serum, this source of error should almost have disappeared. Another mechanism may be prolonged storage of blood at room temperature or in the cold before performing the test, most likely since unphysiological conditions and/or shortage of metabolic fuels may impair Na/K-ATPase activity in leukocytes, ensuing in K release from these cells. For these reasons, it is commonly advised that patients with extreme leukocytosis should have K levels determined on plasma samples that are separated promptly from the cellular elements. We have recently observed a case of pseudohyperkalemia in a patient with chronic lymphocytic leukemia which was unrelated to both of these mechanisms, and was instead related to a common mode of drawing blood, i.e. with vacuum tubes.