Reverse pseudohyperkalemia is more than leukocytosis: a retrospective study

Background. Hyperkalemia is a potentially life-threatening electrolyte abnormality that often requires urgent treatment. Clinicians should distinguish true hyperkalemia from pseudohyperkalemia and reverse pseudohyperkalemia (RPK). RPK has exclusively been described in case reports of patients with hematologic malignancies (HMs) and extreme leukocytosis [white blood cell (WBC) count>200 x 10(3)/mL]. Methods. This single-center retrospective study analyzed laboratory data from the Mount Sinai Data Warehouse between 1 January 2010 and 31 December 2016 for plasma potassium and serum potassium samples drawn within 1h of each other, with plasma potassium >= 1mEq/L of the serum potassium. Only plasma potassium >= 5mEq/L were included. Samples that were documented to be hemolyzed or contaminated were excluded. Clinical history and laboratory data were collected from the identified cases. Results. After applying the inclusion/exclusion criteria to 485 potential cases, the final cohort included 45 cases from 41 patients. There were 24 men and 17 women with a mean age of 52years. The median plasma potassium was 6.1mEq/L and serum potassium was 4.4mEq/L. The median WBC count was 9.35x10(3)/mL (interquartile range 6.5-19.7 x 10(3)/mL). Only 44% of the samples had leukocytosis, defined as WBC >11 x 10(3)/mL. Seven patients had a HM and comprised 11 of the cases (24%) with a median WBC of 181.8 x10(3)mu L. There was no difference in their plasma and serum potassium levels when compared with the total cohort, despite a higher median WBC count. Thirty-eight percent of the cases required medical management. Conclusions. The literature on RPK is limited to case reports and series associated with extreme leukocytosis. This is the first study characterizing RPK predominantly associated with normal leukocyte counts. Further investigation is required to more precisely characterize factors associated with RPK and to elucidate RPK mechanisms.