Pseudohyperkalemia refers to apparent hyperkalemia in a serum sample caused by release of potassium from red blood cells, white blood cells and/or platelets in vitro during storage. Failure to recognize the condition can result in unnecessary treatment of the patient. The authors are from SUNY Health Science Center at Brooklyn in New York City.
Criteria for pseudohyperkalemia:
(1) elevated serum potassium level
(2) (serum potassium level) - (plasma potassium level) > 0.4 mmol/L
(3) exclusion of specimen hemolysis
where:
• The normal difference between serum and plasma potassium is about 0.2 mmol/L.
• Prompt separation of serum or plasma from the cellular elements would minimize the effect, while prolonged storage would increase it.
• The potassium release is associated with platelet aggregation or storage of white blood cells in the refrigerator.
• A release of potassium may go unrecognized if the preceding potassium level is decreased.
Conditions associated with pseudohyperkalemia:
(1) myeloproliferative disorder (with leukocytosis)
(2) leukemia (with leukocytosis)
(3) Hodgkin's disease
(4) infectious mononucleosis (with leukocytosis)
(5) rheumatoid arthritis (with thrombocytosis)
(6) thrombocytosis (results in an increase of 0.15 mmol/L for every 100,000 per µL)
(7) familial pseudohyperkalemia (related to a defect in the red blood cell membrane)
where:
• The increase in potassium may occur with primary or secondary (post-splenectomy, etc.) thrombocytosis.
• A white blood count > 50,000 per µL is typically necessary for leukocytosis to explain pseudohypkalemia (Miller).
