Reliability of point of care potassium measurement confirmed

Blood gas analysis has been performed at the point of care for well over 20 years and is sufficiently established for clinicians to have no misgivings about using pH, pCO₂ and pO₂ results obtained at the point of care for direct patient management. 

Modern blood gas analyzers now have the capacity to measure not only these blood gas parameters, but also an ever-increasing repertoire of chemical and hematological parameters that were once the preserve of the central laboratory. 

Clinician confidence in these new test modalities is now essential for the full potential of the modern blood gas analyzer to be exploited at the point of care. This issue is addressed in a recently published study examining clinician confidence in potassium results obtained using a point-of-care blood gas analyzer. 

A survey of 64 acute care doctors (all grades) working at a UK hospital revealed that although nearly all (94 %) thought blood gas analyzers were a useful method to obtain rapid potassium results, only half (48.4 %) relied solely on blood gas analyzer results to make important clinical decisions. The rest stated that they would wait for central laboratory confirmation of the potassium result before making clinical decisions. 

To examine whether this lack of confidence in blood gas analyzer potassium results, expressed by half the clinicians, is justified, the authors retrospectively compared 529 paired potassium results obtained by blood gas analyzer and central laboratory analyzer on samples taken at the same time from 121 critically ill patients. 

There was good agreement between the two methods. The difference between means of potassium values for the two methods was 0.03 mmol/L. For 95 % of the pairs, potassium concentrations were within 0.5 mmol/L of each other. 

The authors conclude that they have provided evidence that clinical decisions can be reliably made using potassium results obtained by the blood gas analyzer. Such results are “useful, valid and more rapidly available than results from formal laboratory analysis”.