Background: Electrolyte values are measured both by arterial blood gas (ABG) analyzers and central laboratory autoanalyzers (AA), but a significant time gap exists between the availability of both these results, with the ABG giving faster results than the AA. The authors hypothesized that there is no difference between the results obtained after measurement of electrolytes by the ABG analyzers and AA. Methods: We retrospectively analyzed the 122 sets of arterial blood samples from critically ill patients. Whole blood electrolytes were analyzed using a pointofcare blood gas (ABG) analyzer and serum electrolytes were analyzed in the central laboratory autoanalyzers. Results: There was a significant difference in the mean (± standard deviation) sodium value between whole blood and serum samples (134.59±13.11 Vs 144. 20±14.11). There was a significant difference in the potassium values measured by ABG analyzers and AA (3.37±0.68 Vs 3.52 ±0.70). The correlation coefficient obtained for sodium was 0.931 and correlation coefficient obtained for potassium was 0.894. Conclusion: Results with two different measurement technologies differed significantly for plasma sodium and potassium concentrations.Therefore, clinicians should be careful when diagnosing sodium and potassium ion imbalance in critically ill patients and providing treatment.