Discrepancies in Serum Sodium Concentrations Determined by Direct versus Indirect Ion-Selective Electrodes (ISE) Associated with the Serum Total Protein Concentration
The serum protein concentration influences the serum sodium concentration determined by an indirect ion-selective elctrode (ISE). This can cause a result discrepant from the serum concentration reported by a direct ISE.
Direct ISE are typically found in point of care instruments.
Indirect ISEs are typically found in the main chemistry analyzers.
Serum Total Protein
Serum Sodium by Indirect ISE
high
lower than by direct ISE
low
higher than by direct ISE
serum sodium discrepancy between direct and indirect ISE =
= (serum sodium concentration by indirect ISE) – (serum sodium concentration by direct ISE)
Many instances of discrepancies occur in the ICU since many of the patients have hypoproteinemia.
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