Pseudohyperkalemia has been defined as a marked increase of in vitro serum potassium levels in the absence of clinical evidence of electrolyte imbalance. So while true hyperkalemia is a potentially life-threatening clinical condition needing immediate medical intervention, pseudohyperkalemia exhibits no toxic affects because the increased potassium values does not reflect the actual in vivo potassium levels. However, pseudohyperkalemia can be quite misleading, and when overlooked could lead to inappropriate treatment and potentially detrimental therapy.
So what are some causative factors of pseudohyperkalemia? The list is quite extensive. Variables include collection technique such as fist clenching, mechanical trauma during or after phlebotomy, potassium contamination (i.e. carry over from K+-EDTA or oxalate/fluoride tubes), refrigeration before centrifugation, delay in centrifugation, decreased transport or storage temperature, pneumatic tube transport, hemolysis and clotting. Clinical conditions of leukocytosis (i.e. chronic lymphocytic leukemia, infectious mononucleosis), thrombocytosis (i.e. myeloproliferative disorders), abnormal erythrocyte morphology (i.e. familial pseudohyperkalemia), renal disease and rheumatoid arthritis have all exhibited factitious hyperkalemia at one time or another. Additionally, there is reverse pseudohyperkalemia - pseudohyperkalemia with a twist where in increased potassium levels are detectable in plasma while serum samples are within normal range. Here the interaction of heparin with cell membranes is thought to be the culprit.
Although the differentiation of pseudohyperkalemia from true hyperkalemia may be difficult to ascertain, we as laboratory professionals are provided with the opportunity to troubleshoot erroneous lab results for our healthcare team and provide good patient care. What is the incidence of hyperkalemia at your institution? Could some of these “high” potassium levels be attributed to specimen handling? Perhaps your laboratory has identified additional preanalytical or analytical laboratory variables linked to falsely elevated potassium that you would like to share. I invite your comments. For the case of pseudohyperkalemia, identification of the underlying cause is the key.