Pseudohyperkalaemia is defined as a rise in serum potassium with concomitantly normal plasma potassium. The case of long undiagnosed pseudohyperkalaemia in an 84-year-old lady with thrombocytosis post splenectomy is presented. Presenting a historical perspective and the multifactorial aetiology of pseudohyperkalaemia the author underlines the importance of detecting apparent hyperkalaemia by testing the plasma potassium. Awareness of the possible causes of pseudohyperkalaemia increases the likelihood of it being detected earlier thereby decreasing the risk of harming the patient. Unnecessary treatment and investigation of pseudohyperkalaemia can cause harm to the patient in the form of undesired side effects, unnecessary investigations and concerns, and potentially dangerous iatrogenically induced cardiac arrhythmias.