Increasing Glucose Concentrations Interfere with Estimation of Electrolytes by Indirect Ion Selective Electrode Method

Abstract

The estimation of electrolytes like sodium (Na(+)), potassium (K(+)) and chloride (Cl(-)) using direct and indirect ion-selective electrodes (ISE) is a routine laboratory practice. Interferents like proteins, triglycerides, drugs etc. are known to affect the results. The present study was designed to look into the effect of increasing glucose concentrations on estimation of Na(+), K(+) and Cl(-) by direct and indirect ISE. Pooled sera was mixed with glucose stock solution (20 g/dL) prepared in normal saline to obtain glucose concentrations ranging from ~100 to ~5000 mg/dL. Na(+), K(+) and Cl(-) levels were estimated by direct and indirect ISE analyzers and results were statistically analysed using ANOVA and Pearson's correlation. Similar experiment was also performed in 24 h urine sample from healthy subjects. Significant difference was observed between Na(+) and Cl(-) measurements by direct and indirect ISE, with indirect ISE values being consistently higher than direct ISE. Besides this, significant difference was observed amongst Na(+) and Cl(-) values from baseline values obtained by indirect ISE at glucose concentrations ≥2486 mg/dL. However, no such difference was observed with direct ISE. Na(+) and Cl(-) estimation by indirect ISE showed significant negative correlation with glucose concentration, more so, above ~2000 mg/dL. K(+), however, showed no significant difference with varying glucose. Similar results were observed in 24 h urine samples with a significant difference observed amongst Na(+) and Cl(-) values at ≥2104 mg/dL glucose. Thus we conclude that high glucose concentrations interfere significantly in estimation of Na(+) and Cl(-) by indirect ISE in serum as well as urine.

Unbalanced intakes of sodium and potassium among Tunisian adults: A cross‐sectional study

“…The indirect potentiometric method was used to measure urinary sodium levels. A negative bias might be reported in case of higher amounts of glucose excreted in urine (Goyal et al., 2016).…”

Pseudohyponatremia: Mechanism, Diagnosis, Clinical Associations and Management

“…The effect of very high glucose concentrations on the measurement of sodium concentration with ISE methods need further studies. In samples with extremely high glucose concentrations, one study reported finding spuriously high sodium concentrations when the [Na] S was measured using a direct ISE, but not for an indirect ISE [ 130 ], while a second study reported spuriously high sodium concentrations measured with an indirect ISE, but not with a direct ISE [ 131 ].…”

Molecular and physical technologies for monitoring fluid and electrolyte imbalance: A focus on cancer population

“…111 The accuracy of such methods of serum electrolytes estimation has been validated in standard clinical laboratories. 111,112 However, due to the additional preanalytical ions, the ratio of ion to water in serum is altered erratically, leading to inaccurate evaluations when ions are measured indirectly, which are rare and due to a preanalytical error. Another example is vacutainer tubes containing a Na-based anticoagulant, such as Na-heparin, Na-fluoride, Na-citrate, or Na-EDTA, which can markedly elevate plasma Na levels.…”

“…An advantage of diluting the sample is that the measured activity better approximates the concentration, and consequently, indirect ISE results match those obtained using the other biochemistry analysis 111 . The accuracy of such methods of serum electrolytes estimation has been validated in standard clinical laboratories 111,112 . However, due to the additional preanalytical ions, the ratio of ion to water in serum is altered erratically, leading to inaccurate evaluations when ions are measured indirectly, which are rare and due to a preanalytical error.…”