We describe a patient with hyperkalaemia due to localised rhabdomyolysis caused by upper limb ischaemia. Initially, this was erroneously classified as pseudohyperkalaemia, as an earlier measurement of potassium concentration in a venous sample from the contralateral arm was within the reference range. Detailed scrutiny of pathology test results from a second sample by laboratory staff revealed high concentrations of creatine kinase and lactate dehydrogenase, raising the possibility of rhabdomyolysis caused by localised ischaemia. This led clinical staff to reassess the patient, confirming a local arterial occlusion in the arm. This was successfully treated with embolectomy. This report highlights the importance of systematic scrutiny of pathology results, especially when they do not fit the “clinical picture”, and the crucial role of the laboratory in Crit Care Resusc 2009; 11: 219–221 aiding the clinician.