Pseudohyperkalemia in serum: a new insight into an old phenomenon

Abstract

Pseudohyperkalemia, a rise in serum potassium concentration with concurrently normal plasma potassium concentration, is an in vitro phenomenon that was first described 50 years ago. It was originally attributed to the release of potassium from platelets during platelet aggregation and degranulation, and a significant correlation between pseudohyperkalemia and platelet count was established. During the last decade, new data were added to this phenomenon. In particular, pseudohyperkalemia was defined when serum potassium concentration exceeded that of plasma by more than 0.4 mmol/L provided that samples are collected under strict techniques, remain at room temperature and are tested within 1 hour from blood specimen collection. Moreover, it is positively correlated to (1) thrombocytosis due to the release of potassium from platelet granules during coagulation, (2) erythrocytosis due to the dilution of the released potassium in smaller volumes of serum, and (3) the presence of activated platelets, which have the capability of aggregation at a higher speed and release more potassium during degranulation. However, pseudohyperkalemia may be "masked" when in a state of hypokalemia because potassium moves back into the intracellular space in vitro, and the phenomenon is ameliorated or even not detected.

Figure 1.

Changes in plasma potassium concentration (Pk) and serum potassium concentration minus plasma potassium concentration (Dk) in relation to platelet count (PLT) in a patient with thrombocytosis due to myeloproliferative disorder and severe hypokalemia due to excessive use of furosemide. The patient was treated with hydroxyurea and potassium supplements and a sudden increase of Dk was observed 5 days later, when Pk levels reached to 3 mmol/L, despite the decrease of platelet count to 500,000/mm3. Reprinted from Sevastos et al (J Lab Clin Med 2006;147:139–144) with permission from Elsevier. Copyright 2006 Elsevier.