[Pseudo-hypercalcemia of erythrocytic origin. Increased passive membrane permeability to potassium]

Pseudo-hyperkaliemia is a biochemical abnormality suspected when the blood level of K is increased, contrasting with the absence of usual symptoms of hyperkaliemia. The diagnosis is confirmed by the discrepancy between K+ blood levels which are normal if measured immediately after the blood sample is drawn, and increased if the blood sample is incubated at room temperature. In our case, the pseudo-hyperkaliemia is due to the passage of K outside the erythrocytes through increased passive membrane permeability to K. In vivo, this increased passive outflow of K seems to be compensated by an increased active inflow of K dependent on the sodium pump. This explains the absence of true hyperkaliemia and clinical symptoms. In vitro, it seems that the sodium pump is no longer able to ensure this increased activity. Therefore, the abnormality becomes overt, mirrored by a delayed increase in kaliemia.