Reliability of venous blood gas sodium, potassium and creatinine

To determine the level of correlation between sodium, potassium and creatinine readings between point-of-care venous blood gas (VBG) and laboratory biochemistry measurements (LBM).

Data was obtained from three Monash Health (one of the largest health networks in metropolitan Melbourne) emergency departments. 16,527 VBGs were matched with LBM for sodium, 16,437 for potassium and 8,597 for creatinine. Pearson correlation and further subgroup analyses were carried out to explore if acid-base imbalance affected sodium, potassium or creatinine reliability in VBG.

The range of VBG values showed more variation in comparison to LBM. There was good correlation (r>0.8, p<0.001) between measured values with the exception of potassium in acidaemia, however, there was consistent and statistically significant difference in measured values.

The small mean differences across all three parameters observed although statistically significant are unlikely to be clinically significant. With minor calibrations, this would be an easily corrected problem. As such, we recommend that sodium, potassium and creatinine measurements can be used interchangeably between the VBG and LBM, with the exception of potassium levels in acidaemia. Potassium levels in acidaemia should be used with caution due to lower correlation.