An unusual cause of ‘hyperkalaemia” was observed in a neurosurgical patient admitted to our intensive care unit. The cause of the hyperkalaemia was not known initially and treatment with cation ion exchange resin was initiated to lower the elevated serum potassium level. The concurrent occurrence of thrombocytosis and hyperkalaemia raised the possibility of psuedohyperkalaemia associated with thrombocytosis. Simultaneous measurement of plasma and serum potassium with the Hitachi 917 Analyzer (indirect ion selective electrode, coefficient of variation = 1% to 2%) confirmed the diagnosis. Correlation between thrombocytosis and pseudohyperkalaemia was found to be highly significant (r = 0.54; P = 0.014). It is estimated that for every 100 × 109/L of platelets, an increase of 0.07 to 0.15 mmol/L of potassium is expected. In thrombocytosis, plasma rather than serum potassium should be measured.
Hyperkalaemia is a common biochemical derangement in the intensive care unit reflecting a diversity of systemic perturbations such as acute renal failure, rhabdomyolysis, extracellular ionic shift from acid-base anomalies and tissue trauma. We report a rare and erstwhile unencountered cause of serum hyperkalaemia in our intensive care unit (ICU), which was determined to be due to pseudohyperkalaemia from reactive thrombocytosis.
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