Hyperleukocytosis: pseudohyperkalaemia and other biochemical abnormalities in hyperleukocytosis.

A 66-year-old woman, recently diagnosed with T cell prolymphocytic leukaemia (PLL) was admitted for cytotoxic therapy, with a potassium (K) of 5.5 mmol/L on admission as measured on a lithium heparin plasma sample (Beckman DxC800; Beckman Coulter Diagnostics, Fullerton, CA, USA). The sample was analysed within 70 min of collection. The white blood cell count (WBC) was 460=10/L (Sysmex XE5000; Sysmex, Kobe, Japan). The full biochemistry results excluded acidosis, renal failure, tumour lysis syndrome, IV contamination, haemolysis, or EDTA contamination, and the patient had a normal ECG. The elevated K result led to commencement of resonium to lower the K, and this continued until day 2. Resonium (A) is a cation-exchange resin which lowers the blood potassium level by exchanging potassium for sodium in the intestine. On day 2, a K of 9.0 mmol/L was obtained, and the result was immediately phoned to the clinical unit. The medical staff were appropriately notified that this result was probably artefactual and the resonium was ceased after a venous blood gas sample was collected, and a K of 4.0 mmol/L obtained (Rapidlab 1265; Siemens Healthcare Diagnostics, Medfield, MA, USA). Pseudohyperkalaemia is well-documented in hyperleukocytosis, particularly with chronic lymphocytic leukaemia (CLL) (1–3). Despite most haematologists and emergency physicians being aware of this phenomenon, under some circumstances hyperkalaemia might be misinterpreted. We frequently observe initiation of treatment to lower K, usually in Emergency or Haematology Units, with the potential to cause in