title: Establishing evidence-based thresholds and laboratory practices to reduce inappropriate treatment of pseudohyperkalemia.
abstract: BACKGROUND
  Unrecognized pseudohyperkalemia (PHK), defined as an artificial increase in measured potassium concentration, due to thrombocytosis and leukocytosis can lead to inappropriate patient treatment. Understanding the laboratory and patient characteristics that increase risk of PHK is key to preventing diagnostic errors.
  
  
  METHODS
  Serum/plasma potassium results collected at 2 laboratories over 4years were selected based on blood cell counts collected within 24h and whole blood potassium concentrations determined within 2h of the serum/plasma sample. Differences between whole blood and serum or plasma potassium were compared as functions of platelet or leukocyte count, fit to linear models, and stratified based on leukemia diagnosis codes. Patients having a serum/plasma potassium concentration that was at least 1mEq/mL higher than the whole blood concentration were defined as having PHK. Based on this analysis, high-risk patients were prospectively identified and PHK risk was communicated to providers. Medication administration records were queried to compare rates of kayexalate use pre- and post-intervention.
  
  
  RESULTS
  Approximately 14% of serum samples with platelet counts >500×109/L had a>1mEq/L increase relative to whole blood potassium. >25% of serum and plasma samples showed a>1mEq/L increase relative to whole blood potassium when leukocyte counts were >50×109/L. Patients with chronic lymphocytic leukemia and high WBC count demonstrated the highest rates of PHK. The rate of kayexalate administration prior to confirmatory testing decreased from 37% to 16% after the laboratory started verbally communicating the possibility of PHK to treating providers.
  
  
  CONCLUSIONS
  According to our data, a leukocyte count threshold for plasma samples of 50×109/L is appropriate for indicating a high risk of PHK. Direct communication by the laboratory to the care team reduces inappropriate potassium lowering treatment in populations at high risk.
authors.affiliation: Department of Laboratory Medicine, University of Washington, Seattle, WA 98195, United States.
authors.forename: Pratistha
authors.initials: P
authors.lastname: Ranjitkar
authors.affiliation: Department of Laboratory Medicine, University of Washington, Seattle, WA 98195, United States.
authors.forename: Dina N
authors.initials: DN
authors.lastname: Greene
authors.affiliation: Department of Laboratory Medicine, University of Washington, Seattle, WA 98195, United States; Department of Pathology, University of Washington, Seattle, WA 98195, United States.
authors.forename: Geoffrey S
authors.initials: GS
authors.lastname: Baird
authors.affiliation: Department of Laboratory Medicine, University of Washington, Seattle, WA 98195, United States; Department of Medicine, University of Washington, Seattle, WA 98195, United States.
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Hoofnagle
authors.affiliation: Department of Laboratory Medicine, University of Washington, Seattle, WA 98195, United States. Electronic address: pcm10@uw.edu.
authors.forename: Patrick C
authors.initials: PC
authors.lastname: Mathias
mesh_terms: D001792:Blood Platelets / Q000378:metabolism / Q000473:pathology*; D002614:Chelating Agents / Q000009:adverse effects; D003951:Diagnostic Errors; D006801:Humans; D006947:Hyperkalemia / Q000097:blood / Q000175:diagnosis* / Q000209:etiology / Q000473:pathology; D007958:Leukocyte Count; D007962:Leukocytes / Q000378:metabolism / Q000473:pathology*; D007964:Leukocytosis / Q000097:blood / Q000150:complications / Q000175:diagnosis* / Q000473:pathology; D016014:Linear Models; D010976:Platelet Count; D011137:Polystyrenes / Q000009:adverse effects; D011188:Potassium / Q000097:blood*; D012189:Retrospective Studies; D013922:Thrombocytosis / Q000097:blood / Q000150:complications / Q000175:diagnosis* / Q000473:pathology
chemical_list: D002614:Chelating Agents; D011137:Polystyrenes; C003321:polystyrene sulfonic acid; D011188:Potassium
keywords: Diagnostic error; Hyperkalemia; Leukocytosis; Pseudohyperkalemia