Near-patient testing of potassium levels using arterial blood gas analysers: can we trust these results?

BACKGROUND: Near-patient testing allows rapid availability of results to enable prompt decision-making. Potassium abnormalities are common in acutely ill patients and can be associated with life-threatening complications. At times there is uncertainty whether clinical decisions can be based on the potassium result obtained from arterial blood gas (ABG) analysers or if laboratory values should be awaited.
OBJECTIVES: To determine the opinion of clinicians regarding the use of blood gas analysers to measure potassium and to determine the level of agreement between blood gas analyser and laboratory measurements of potassium in arterial blood samples.
METHOD: Survey of 64 doctors using a questionnaire and a retrospective comparative study of 529 paired results of ABG and arterial laboratory measurements of potassium in 121 critically ill patients.
RESULTS: 51.6% of the doctors would wait for laboratory confirmation and 48.4% would base clinical decisions on results obtained from the blood gas analyser. The difference between the means of potassium values from the two methods is 0.03 mmol/l (95% CI 0.011 to 0.056; p = 0.0041). The 95% limits of agreement were from -0.485 mmol/l (95% CI -0.524 to -0.447) to 0.551 mmol/l (95% CI 0.513 to 0.590). 95% of the results fell within the difference limits of 0.5 mmol/l.
CONCLUSIONS: Most clinicians still await laboratory confirmation of results obtained from blood gas analysers but in this setting there is sufficient agreement between the results obtained from the authors' blood gas analyser and a laboratory analyser to enable effective clinical decisions to be made.