Pseudohyperkalemia

Pseudohyperkalemia is an in vitro artifact in which potassium levels appear elevated in blood samples but do not reflect the patient’s true in vivo serum potassium. It is a laboratory phenomenon rather than a physiological condition, and it can lead to misdiagnosis and inappropriate treatment if not recognized.

The most common contexts involve markedly increased numbers of circulating cells, especially leukocytes or platelets. Severe leukocytosis (as seen in some leukemias and myeloproliferative disorders) or thrombocytosis can cause potassium to be released from cells during or after phlebotomy, clotting, or sample processing. Other contributing factors include hemolysis from difficult collection, excessive fist clenching, prolonged tourniquet use, inappropriate tube handling, and delays in separating serum or plasma. In serum samples, potassium is released from platelets during clotting, which tends to raise serum potassium relative to plasma.

Diagnosis relies on recognizing discordance between serum and plasma potassium and the clinical context. If hyperkalemia is suspected but there are no compatible clinical signs and the patient has marked leukocytosis or thrombocytosis, repeat testing using plasma potassium (or a rapid whole-blood/arterial sample) after careful handling. Normal plasma potassium with elevated serum potassium strongly suggests pseudohyperkalemia. It is important to assess for hemolysis indicators in the sample and to consider alternative testing methods to avoid unnecessary treatment.

Management focuses on avoiding unnecessary hyperkalemia treatment and addressing the underlying cause. Clinicians should verify results with repeat testing using appropriate sample handling and, when genuine hyperkalemia is present, follow established guidelines to reduce potassium safely.