Benefit of point of care testing in patient with major hyperleukocytosis

We report a case of a child with major leukocytosis (800 × 10⁹/L) leading to a false increase in plasma potassium and an unexpected spurious decrease in sodium. To suppress interferences due to hyperleukocytosis, our laboratory protocol consists of collecting blood on Clotting Activator/Serum tubes (CAS) and/or carrying samples by human courier. CAS tube analysis showed a decreased level of hyperkalemia and sodium within the reference range (consistent with point of care measurements). Pseudo-hyperkalemia caused by extreme hyperleukocytosis has been well documented and is caused by lysis of leukocytes and cell contents release (including potassium) into the plasma, especially regarding blast cells, which are at even higher risk of lysis. Pseudo-hyponatremia mechanism has not yet been described. This interference could be multifactorial; blast lysis could cause intracellular ionic content release, therefore, modifying extracellular fluid ionic ratios. To correct this interference, the hypothesis is that collecting samples on CAS tubes or monitoring patient using point of care analysis are the most efficient solutions, as transport mode did not resolve interference issues. We speculate that cell lysis related to interference is multifactorial but mainly caused by centrifugation. To confirm this, we would have liked to compare ion levels before and after centrifugation.