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Abstract: FR-PO561

Comparison of i-STAT Point of Care vs. Indirect Ion Selective Electrode Measurements of Sodium in Severe Hyponatremia

Session Information

Category: Fluid‚ Electrolyte‚ and Acid-Base Disorders

  • 1002 Fluid‚ Electrolyte‚ and Acid-Base Disorders: Clinical

Authors

  • Gomez, Daniel G., University of Massachusetts Chan Medical School - Baystate Regional Campus, Springfield, Massachusetts, United States
  • Hodgins, Spencer, University of Massachusetts Chan Medical School - Baystate Regional Campus, Springfield, Massachusetts, United States
  • Paramasivam, Vijayakumar, University of Massachusetts Chan Medical School - Baystate Regional Campus, Springfield, Massachusetts, United States
  • Landry, Daniel L., University of Massachusetts Chan Medical School - Baystate Regional Campus, Springfield, Massachusetts, United States
  • Mulhern, Jeffrey, University of Massachusetts Chan Medical School - Baystate Regional Campus, Springfield, Massachusetts, United States
  • Nathanson, Brian Harris, University of Massachusetts Chan Medical School - Baystate Regional Campus, Springfield, Massachusetts, United States
  • Braden, Gregory Lee, University of Massachusetts Chan Medical School - Baystate Regional Campus, Springfield, Massachusetts, United States
Background

We sought to determine whether point-of-care (POC) sodium (Na) levels by I-STAT were accurate enough compared to Main Lab sodium measured by ion-specific electrode technique (the “Gold Standard”) to allow for its use in monitoring the administration of 3% hypertonic saline to correct severe hyponatremia.

Methods

We extracted all consecutive data from Baystate Medical Center inpatients with Na < 135 mmol/L from January 2015 to December 2019 who had a POC and Main Lab Na level within 30 minutes of each other. This was a venous-to-venous comparison using direct ion-selective electrode by I-STAT vs indirect ion-selective electrode by Main Lab. We compared values with a Bland-Altman plot and repeated the analysis with Main Lab sodium < 125 mmol/L.

Results

We obtained 406 Na paired samples from 355 patients. The bias (i.e., mean difference) of POC - Main Lab was significantly greater than 0; 1.2 mmol/L; 95% CI (0.8-1.5); p<0.001. Severe hyponatremia samples < 125 mmol/L (n = 44) demonstrated a larger bias with a disagreement by as much as 10 mmol/L: bias = 1.7 mmol/L, 95% CI (0.3-3.1); p = 0.003.

Conclusion

I-STAT POC significantly overestimates Na levels when compared to Main Lab indirect ion-selective electrode analysis when Na is either < 135 mmol/L or < 125 mmol/L. The use of POC for monitoring Na levels during 3% hypertonic saline administration in severe hyponatremia is not recommended.