AbstractObjectivesStudy and management of a case with elevated potassium levels without apparent clinical causes in successive follow-up visits.Case presentationWe present the case of a primary care female patient who persistently exhibited elevated levels of potassium (5.3–5.9 mmol/L) in successive control laboratory tests, without an apparent clinical cause. The patient was ultimately referred to the Unit of Nephrology, where a potassium-low diet was indicated. Diet did not have any effect on potassium levels. After a thorough study, the cause of hyperkalemia could not be determined.ConclusionsThe inconsistency between elevated potassium levels and the reason of consultation, and exclusion of other pre-analytical or pathological causes raised suspicion of familial pseudohyperkalemia. The sample was incubated at different times and temperatures to demonstrate their influence on levels of potassium in blood. Familial pseudohyperkalemia was established as the most probable diagnosis. Finally, the patient was discharged from the Unit of Nephrology and instructed to follow a normal diet.