A Brother and Sister with Fluctuating Potassium Concentrations

Abstract

A 61-year-old man was admitted to the emergency department (ED)4 for increased potassium concentration of 6.3 mmol/L (reference interval, 3.5–5.0 mmol/L) that was ordered by the general practitioner as part of a yearly medical checkup. Physical examination did not reveal any symptoms associated with hyperkalemia. Reanalysis of potassium in a new blood sample drawn in the hospital resulted in a value of 3.7 mmol/L. Remarkably, his visit to the ED had been the third one in 3 years' time, all taking place after a yearly medical checkup during the winter season with increased potassium at each visit that was within the reference interval after reanalysis of a new blood sample drawn in the hospital. The patient was referred to an internist for further examination who ordered a potassium analysis 1 month after the last visit to the ED. Again, an increased concentration was noticed (6.6 mmol/L) followed by admission to the emergency room. Reanalysis of potassium in the hospital again showed a healthy potassium concentration (3.6 mmol/L). The patient did not use any medication. On his visit to the internist, he mentioned that 1 year ago his sister was also admitted to the ED for an increased potassium concentration (7.9 mmol/L) that could not be confirmed in a newly drawn blood sample. ### LABORATORY INVESTIGATION The hemolysis index (H-index) of the previously analyzed samples did not reveal hemolysis as an explanation for the potassium increase. The H-index ranged from 4–11 μmol/L, corresponding to a hemoglobin concentration of 6.4–17.7 mg/dL. We did notice that all samples with increased potassium concentrations were drawn in a phlebotomy service center operated by our laboratory between 8 and 9 a.m. and that samples arrived at the central laboratory at 12 p.m. The samples were collected in lithium heparin gel tubes and were centrifuged after arriving at the …