A case of 'reverse' pseudohyperkalemia.

Pseudohyperkalemia is diagnosed when the serum potassium level exceeds the plasma potassium level by 0.4 mmol/l. This is commonly encountered in settings of high leukocyte or platelet counts, since under these conditions, potassium, an intracellular cation, is released in supranormal amounts during the process of clotting. We report an unusual case wherein the reverse was true, i.e., the plasma potassium concentrations was higher than that found in the serum. Heparin, which is known to cause cell lysis, was used as the anti-coagulant in the plasma tubes. We propose that the underlying mechanism in this particular case is a heightened sensitivity to heparin-induced membrane damage in the face of a hematological malignancy.