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• Serum or Plasma? Pseudohyperkalemia in a chronic lymphocytic leukemia patient
  Kenneth A. Hoekstra
  Published on: 11 August 2020

• Published on: 11 August 2020

  Serum or Plasma? Pseudohyperkalemia in a chronic lymphocytic leukemia patient

  • Kenneth A. Hoekstra

  Dear Editor:

  Kapoor et al. (1) investigated pseudohyperkalemia in outpatients and attributed many of the cases to hematological abnormalities or delay in specimen centrifugation or clotting. Plasma is often recommended as the preferred specimen in patients with leukocytosis, erythrocytosis or thrombosis (2). Potassium released from ruptured cells during the clotting process of serum specimens may result in false...

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  Dear Editor:

  Kapoor et al. (1) investigated pseudohyperkalemia in outpatients and attributed many of the cases to hematological abnormalities or delay in specimen centrifugation or clotting. Plasma is often recommended as the preferred specimen in patients with leukocytosis, erythrocytosis or thrombosis (2). Potassium released from ruptured cells during the clotting process of serum specimens may result in false-positive reporting and unnecessary therapy (3). Others have reported on a phenomenon known as reverse pseudohyperkalemia in patients with leukocytosis where potassium concentrations in plasma specimens exceeded concentrations in serum (4).

  We describe a similar case of reverse psuedohyperkalemia. A 87-year- old man with chronic lymphocytic leukemia (CLL) was treated for the past 2 years as an outpatient. He received cyclophosphamide, vincristine, and rituximab chemotherapeutic agents as part of his treatment plan. Blood was collected in serum separator (SST) and EDTA tubes for routine metabolic and hematology studies. The potassium concentration averaged 3.7 mmol/L on a Beckman DXC chemistry analyzer (n=11). His white blood cell (WBC) and platelet counts averaged 306 x 109 cells/L (94-97% lymphocytes) and 95 x 109 platelets/L over this time period. Recently, he was admitted to the ED. Specimens were collected for metabolic (lithium-heparin specimen with separator gel) and hematology (EDTA plasma) analyses. The specimens were transported by pneumatic tube, and time from collection to analysis was <60 min. The potassium concentration was 7.5 mmol/L; similar results were obtained on a second analyzer. No hemolysis was observed. The hematology results supported a known diagnosis of CLL but all other laboratory data was within normal limits. Pseudohyperkalemia was investigated. Additional venous blood specimens were collected in lithium- heparin with a separator gel and a SST tubes. The specimens were immediately transported to the lab by pneumatic tube (<5 min transport time), promptly centrifuged (5 min at 3500 rpm) or allowed to clot (30 min; then centrifuged for 5 min at 3500 rpm) and analyzed. The plasma specimen exhibited significantly higher potassium (7.4 mmol/L) concentration compared with the serum specimen (3.9 mmol/L). A significant layer of WBC was evident on the packed erythrocyte layer in the lithium- heparin tube. No WBC layer was observed in the serum specimen. Four days later, a similar occurrence (lithium-heparin potassium = 6.4; serum potassium = 4.2 mmol/L) was observed on the same in-patient.

  Some cells, especially malignant ones are susceptible to in-vitro heparin-induced cell membrane damage during specimen processing resulting in diffusion of potassium into the supernatant from ruptured leukocytes. Similar cases in other leukemia patients have been observed in our laboratory. Both laboratorians and clinicians should be aware of this phenomenon to minimize false-positive reporting and unnecessary therapy.

  1. A K Kapoor, AK, Ravi A, Twomey PJ. Investigation of outpatients referred to a chemical pathologist with potential pseudohyperkalaemia. J Clin Pathol 2009; 62:920-923.

  2. Ifudu O, Markell MS, Friedman EA. Unrecognized pseudohyperkalemia as a cause of elevated potassium in patients with renal disease. Am J Nephrol. 1992;12(1-2):102-4.

  3. Sevastos N, Theodossiades G, Savvas SP, Tsilidis K, Efstathiou S, Archimandritis AJ. Pseudohyperkalemia in patients with increased cellular components of blood. Am J Med Sci. 2006 Jan;331(1):17-21

  4. Abraham B, Fakhar I, Tikaria A, Hocutt L, Marshall J, Swaminathan S, Bornhorst JA. Reverse pseudohyperkalemia in a leukemic patient. Clin Chem. 2008 Feb;54(2):449-51.

  Conflict of Interest:

  None declared

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  Conflict of Interest:
  None declared.

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