title: Potassium but not lactate dehydrogenase elevation due to in vitro hemolysis is higher in capillary than in venous blood samples.
abstract: BACKGROUND
  Elevated potassium concentrations due to in vitro hemolysis can lead to errors in diagnoses and treatment. Recently, we observed that potassium elevation in capillary samples appeared higher than expected, based on hemolytic index (H-index).
  
  
  OBJECTIVE
  To investigate the relation between potassium increase and H-index for capillary samples. As a control, the same analysis was performed for lactate dehydrogenase (LDH).
  
  
  METHODS
  Potassium results of 332 760 venous and 2620 capillary samples were selected. For LDH, 135 974 venous and 999 capillary samples were included. Venous and capillary samples were differentiated by using patient age, as we perform mostly capillary blood sampling in children and venous sampling in adults. Results were obtained with Beckman-Coulter DxC800 analyzers.
  
  
  RESULTS
  The increase in potassium with increasing H-index was considerably higher for capillary samples than venous samples. Linear regression revealed a potassium increase of 0.38 mEq/L per increment in H-index for capillary samples, whereas a 0.17 mEq/L increase was found for venous samples. For LDH, no differences were found between venous and capillary samples.
  
  
  CONCLUSIONS
  At identical H-index, capillary samples showed higher potassium elevations than venous samples. A possible explanation is that capillary sampling causes increased leakage of ions, such as potassium, from erythrocytes, compared with proteins such as hemoglobin and LDH. These results are especially important considering the increasing use of whole blood point-of-care analyzers, where the H-index is often not determined. Potassium results should therefore be interpreted with caution to avoid severe misdiagnosis of hypokalemia and hyperkalemia.
authors.affiliation: University of Medical Center Utrecht, Laboratory of Clinical Chemistry and Haematology, Utrecht, The Netherlands.
authors.forename: Marlies
authors.initials: M
authors.lastname: Oostendorp
authors.forename: Wouter W
authors.initials: WW
authors.lastname: van Solinge
authors.forename: Hans
authors.initials: H
authors.lastname: Kemperman
mesh_terms: D000293:Adolescent; D000328:Adult; D001774:Blood Chemical Analysis / Q000592:standards*; D002196:Capillaries; D002648:Child; D006461:Hemolysis; D006801:Humans; D007770:L-Lactate Dehydrogenase / Q000097:blood*; D011188:Potassium / Q000097:blood*; D014680:Veins; D055815:Young Adult
chemical_list: D007770:L-Lactate Dehydrogenase; D011188:Potassium