Indirect Ion-selective Electrode Research Articles

Comparison of whole blood potentiometry using arterial blood gas analyser at the intensive care unit with laboratory-based serum sodium and potassium estimation in critically ill patients

BackgroundElectrolyte measurement in critically ill patients is a crucial investigation guiding the management of the patients. Accuracy of the results and rapid turnaround time are hence very important in the analysis of electrolytes. In our study, we aim to compare two methods of electrolyte concentration measurement by direct ion-selective electrodes (direct ISEs) using patient whole blood sample in the intensive care unit (ICU) and indirect ion-selective electrodes (indirect ISEs) using serum sample in laboratory. MethodsA prospective observational study was conducted on 142 paired samples that were obtained from patients admitted to the ICU. The arterial whole blood was analysed in an arterial blood gas analyser located in the ICU for analysis of electrolytes by Direct-ISE, whereas the blood collected for serum electrolytes was promptly transported to the hospital laboratory where serum was separated and analysed in an automated analyser using indirect ISE. Statistical analysis was done by using the t-Test and Bland–Altman plots. The Haemolysis Icteric Lipemia Index given by the laboratory analyser and serum total protein value were also recorded. Results and conclusionIn our study conducted on 142 paired samples for electrolyte analysis in critically ill patients by direct ISE and indirect ISE, we observed that there is a statistically significant difference between the average of measurements by the two methods. This difference is more significant at lower sodium levels and normal potassium levels. A larger sample size is required to shed more light on the clinical implications in the tertiary-care setup where the study was organised.

Rapid microfluidic fluorescence detection platform for determination of whole blood sodium

A novel detection platform consisting of a microfluidic fluorescence reaction chip (FR-chip) and a miniaturized analysis system is proposed for the determination of sodium ions (Na+) in whole human blood samples. In the proposed method, a rapid reaction of sodium green (SG) reagent with Na+ is induced in the microfluidic FR-chip to produce a SG-Na+ complex. The Na+ concentration is then determined using the miniaturized analytical system based on the maximum fluorescence peak of the reaction compound at a wavelength of 533 nm. The experimental results obtained for artificial serum samples with Na+ concentrations ranging from 10 to 200 mM show a relationship between Na+ concentration (Y) and fluorescence intensity (X) as follows: Y = 190.5 ln(X) + 90.15. The correlation coefficient (R2) is 0.9956, and the limit of detection (LOD) is 2.8 mM. Furthermore, the detection results obtained for 90 whole blood samples from chronic kidney disease (CKD) patients exhibit a high level of consistency (R2 = 0.9806) when compared to the detection results obtained using a traditional indirect ion-selective electrode (ISE) method. Overall, the results confirm that the current microfluidic fluorescence detection platform offers a convenient and highly sensitive approach for the point-of-care (POC) monitoring of whole blood Na+ concentrations.

Different serum sodium assay, different model for end stage liver disease - sodium scores in patients awaiting liver transplant: A cross-sectional study.

Sodium can be measured with direct or indirect methods; abnormal plasma total protein concentration can impact on sodium measured by indirect ion-selective electrodes (ISE). Serum sodium is an important item to determine the Model for End Stage Liver Disease Sodium (MELD-Na) score, commonly used for liver graft allocation. Patients with cirrhosis usually have hypoproteinemia. The aim of this study was to determine if there was a significant difference between the MELD-Na scores calculated based on the results of two different serum sodium ISE: indirect and direct. This was a retrospective study; we included 166 patients that underwent liver transplant assessment, and that had paired (i.e. same date and time) direct and indirect sodium determinations. We calculated the MELD-Na scores with both sodium determinations, and we compared them. There was a significant difference between MELD-Na scores; the mean difference was 0.4±1.3. If MELD-Na score had been determined by the sodium measured by the direct ISE, 69 patients (42%) would have stayed in the same place on the waiting list, 67 patients (40%) would have moved up, and 30 patients (18%) would have moved down. There was a statistically significant difference between the MELD-Na scores calculated based on the two different sodium concentrations, which would theoretically result in changes in the order of the waiting list. This finding should prompt studies to assess if MELD-Na calculated based on direct methods has a better performance to predict clinically relevant outcomes.

A comparison of serum sodium levels measured using a colorimetric kit approach and those determined using direct and indirect ion selective electrode techniques- in a Hospital Central Lab

When electrolyte imbalances are not recognized, they are known to cause severe morbidity and mortality. Dyselectrolytemia is frequently curable. Hyponatremia is a common symptom seen in the elderly. Laboratory equipment may be lacking in rural healthcare settings. As a result, the purpose of this study was to investigate the feasibility of developing a screening technique that can aid in the detection of hyponatremia in such facilities. Serum sodium levels in 120 samples were determined by direct, indirect, and colorimetric ISE. SPSS version 17, NCSS 11, and MINITAB 18 software were used for statistical analysis. Statistical significance was defined as a p-value of 0.05. While comparing the instruments, a basic linear regression analysis was performed, and a regression equation for sodium levels was established. The Bland-Altman analysis yielded a 95% agreement limit between the instruments, which is well within the CLIA-recommended target value of 4 mmol/L in the hyponatremic and normonatremic ranges. The resulting regression equation computes a predicted value for direct and indirect ISE using the colorimeter readings, making it similar to all three instruments in the hyponatremic and normonatremic ranges. The colorimetric method can be used as a low-cost screening technique to identify hyponatremic elderly people for whom a tertiary hospital may be inaccessible, allowing for early care.

Paraproteins and electrolyte assays: exclusion effect and effect of paraprotein elimination

Paraproteins are a potential source of error for electrolyte analyses. The exclusion effect itself causes a discrepancy between direct and indirect ion selective electrode assays (dISE and iISE, respectively). We tested the applicability of different pretreatment methods and the difference of dISE and iISE with paraprotein-rich samples. We analysed chloride (Cl-), potassium (K+), and sodium (Na+) on 46 samples with paraproteins up to 73 g/L. We compared pretreatment methods of preheating, precipitation, and filtration to the native sample. All induced a statistically significant difference (p-value <0.05). Clinically significant difference was induced by precipitation for all analytes, and filtration for Cl- and Na+, but for none by preheating. The difference in electrolyte measurements with either dISE or iISE on native samples was explained by total protein concentration (TP). There was a statistically significant difference in all electrolyte measurements. On average, there was a clinically significant difference in Na + but not in Cl- and K + measurements. Paraprotein concentration (PP) or heavy chain class did not induce a statistically significant effect. The regression analysis and comparison to the theoretical exclusion effect supported the conclusion that TP is the only explanatory factor in the difference between dISE and iISE. We conclude that preheating is a suitable pretreatment method for all the studied analytes. Precipitation is not valid for any of them, and filtration can be considered only for K+. Because the difference between dISE and iISE was explained by the exclusion effect caused by TP, dISE is the more suitable method to analyse paraprotein-rich samples.

Comparing the effect of Hypoalbuminemia on Sodium measured by Indirect versus Direct Ion Selective Electrode Method

Objective: To evaluate the effect of low serum Albumin levels on serum sodium measurement when analyzed by the indirect Ion Selective Electrode (ISE) method and to compare the results with the direct Ion selective electrode (ISE) method.&#x0D; Study Design: Cross-sectional study&#x0D; Place and Duration of Study: Department of Chemical Pathology, Armed Forces Institute of Pathology, Rawalpindi Pakistan, from Jan to Mar 2021.&#x0D; Methodology: Patients of either gender, aged 18 to 70 years, who were admitted to the Intensive Care Unit of Combined Military Hospital, Rawalpindi, were selected. A total of 200 blood samples were collected in a gel tube. Serum samples were analyzed for albumin and sodium within two hours of sample collection. Sodium levels were measured concurrently by both direct and indirect ISE methods. The difference in results between these two techniques was studied.&#x0D; Results: Hypoalbuminemia was detected in 176(88%) patients, while 24(12%) had normal albumin levels. In Hypoalbuminemic patients, serum sodium measurements were higher using the indirect ISE method(134.07±5.55) compared to the direct ISE method (130.95±6.04); the difference between the two techniques was statistically significant (p-value &lt;0.001).Pearson correlation coefficient (r-value = -0.86, p-value &lt;0.001) revealed a symmetrical increase in differences between the two methods as the albumin level decreased.&#x0D; Conclusion: In Hypoalbuminemic patients, the indirect ISE method gave falsely raised results of serum sodium. In such patients, serum sodium measurement by the Direct ISE method offers more accurate and consistent electrolyte results.

Close the gap

Background: Serum chloride (Cl-) is measured via direct or indirect ion selective electrodes in most laboratories. There have been reports of falsely elevated Cl- concentrations and a resultant negative anion gap due to interference from drugs containing bromide, which is a negatively charged halide, similar to Cl-.1,2 Case: A 1-year-old girl with severe, treatment resistant epilepsy presented for routine bloods. Her medication history included multiple anti-epileptics including phenobarbitone, clobazam, topiramate, vigabatrin, and also potassium bromide. No abnormality was found on full blood count, thyroid functions tests, liver and kidney function tests apart from a mildly elevated GGT of 30 U/L (RI 5–20 U/L). The anion gap was negative as Cl- was repeatedly unmeasurably high (>150 mmol/L), with the remainder of the electrolytes within normal limits. Review of her medication history prompted the possibility of bromide interference. We measured Cl- and bromide via ICP-MS: Cl- was 69 mmol/L and bromide markedly elevated at 35 mmol/L. Conclusion: Bromide-containing medications can cause a negative anion gap as a result of a falsely elevated chloride concentration. When this is suspected, measurement of chloride via a method different to ISE should be considered.

Low Serum Bicarbonate in a Patient With Diabetes Mellitus:: A Quiz

Low Serum Bicarbonate in a Patient With Diabetes Mellitus:: A Quiz

Laying the foundation for enhancing safety of desmopressin in older people: Validation of capillary blood sodium levels.

We aim to make desmopressin a safe treatment option for (older) patients at risk for hyponatremia, by introducing a new way of sodium monitoring. The goal is to reduce the risk of hyponatremia, enhance patient safety and ultimately introduce self-monitoring of sodium levels. The first step in the aforementioned is to validate capillary sodium. 100 randomly selected patients admitted to the urology department received a single finger prick to collect capillary blood (250 µl) in a lithium-heparin tube. Each patient acted as its own control for the capillary and venous blood sample. Venous and capillary plasma sodium were analyzed by indirect ion-selective electrodemeasurement. The primary outcome was the agreement between capillary and venous sodium measurements, measured by the intra-class correlation coefficient (ICC). One hundred paired blood samples were obtained of which four were excluded. There was no significant statistical difference observed between venous and capillary sodium (-0.23 mmol/L, p = 0.374). The ICCfor single measures between capillary and venous sodium was 0.82 (95% confidence interval 0.75-0.88). Inter-method differences analyzed by a Bland-Altman plot and a Passing-Bablock regression did not reveal a statistically significant difference between both groups. We demonstrated that venous and capillary sodium levels are interchangeable, taken into account the inter- and intravariability between analyses. We provided the first step towards a simple and safe solution for frequent sodium monitoring through a minimal invasive capillary blood collection. The results are of direct clinical relevance to safely use desmopressin in (older) patients at risk.

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

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

Impact of Time Delay in the Analysis of Serum Ionized Calcium, Sodium, and Potassium.

Introduction Delay in the analysis of serum electrolytes along with clot contact time can lead to difference in results significant enough to affect clinical decisions. This study was undertaken to evaluate the effect of time lag between centrifugation and analysis on levels of serum sodium, potassium, and ionized calcium in a tertiary level health care set up. Materials and Methods In this cross-sectional study, 70 serum samples were analyzed for ionized calcium, sodium, and potassium under different conditions with respect to time lag and clot contact time. The analysis of ionized calcium was done on Eschweiler Combiline 2, a direct ion-selective electrode (ISE) analyzer. Serum sodium and potassium were analyzed on fully automated chemistry analyzer, which is an indirect ISE analyzer. The statistical analysis was done in IBM SPSS software version 21. Results The results for intergroup comparison with different time lag and clot contact time between all the four groups for sodium, potassium, and ionized calcium were statistically significant, as obtained by application of Kruskal-Wallis test. There was consistent decrease in the concentration of sodium and ionized calcium, and an increase in serum potassium with increased delay in analysis and clot contact time. Conclusion The accurate measurement of electrolytes is of paramount importance for the treatment and better prognosis of critically ill patients. This can be accomplished by better management of the preanalytical phase of analysis by maintaining a standard protocol in the laboratory and sample transportation.

Resolving Pseudohyponatremia: Validation of Plasma Sodium on Radiometer ABL800 Blood Gas Analyzers for Immediate Reflex Testing.

To perform validation of plasma sodium on blood gas analyzers to reflexively correct erroneous measurements by ion-selective electrodes (ISEs). We compared remnant specimens of whole blood and plasma collected by lithium heparin vacutainer with normal protein concentrations and no lipemia. Whole-blood specimens were tested for sodium concentration on the ABL800 Flex blood gas analyzer, followed by centrifugation for plasma separation, and repeat sodium determination on an aliquot of the plasma only. Also, plasma specimens were analyzed by indirect ISE on the Cobas 8000 series and by direct ISE on the ABL800 Flex for instrument comparison. Plasma aliquots yielded comparable results to the parent whole-blood specimen, with an average change of -1.33 mmol/L (R2 = 0.9727). Comparison of indirect ISE to direct ISE similarly yielded comparable results, with an average change of + 0.8 mmol/L (R2 = 0.9016). Plasma is a valid specimen matrix for use on blood gas analyzers for sodium determination, eliminating the need for re-collection of whole-blood specimens from patients with pseudohyponatremia.

Asparaginase-induced pseudohyponatremia, a case-driven working strategy in pediatric patients

ABSTRACT Objectives When using indirect ion-selective electrode (ISE) methods, hypertriglyceridemia leads to pseudohyponatremia due to water displacement artifacts. Multiple strategies exist to minimize this interference. Our objective was to create a patient-friendly one-tube-fits-all testing setup without compromising the method robustness. Methods Four strategies were evaluated in a single patient with hypertriglyceridemia. Additionally, the interchangeability between the Cobas 8000 and ABL Flex was evaluated on samples (n = 2274) with different total protein (TP) concentrations. Finally, a proof-of-concept (n = 40) was performed by re-measuring the routine sample with the ABL90 Flex. Results ABL90 flex results and calculated sodium did not suffer from the presence of high triglyceride levels. We did not observe any significant differences between the three groups (P > 0.05) of sample types (arterial vs. venous plasma vs. venous whole blood after mixing up) nor for the analysers (Roche vs. ABL90 Flex). Passing–Bablok and Bland–Altman tests revealed interchangeability. Conclusion In future cases of hypertriglyceridemia, 1500 mg/dL will be used as a preliminary threshold for reliable sodium determination. Routine Li-heparin samples can be used for accurate sodium determination without any need for extra arterial or venous blood gas tubes, offering a patient-friendly test setup for similar cases.

Pre-analytical phase impact in the differences in natremia obtained by direct and indirect ion selective electrodes methods

Natremia is an important biological parameter providing information on the hydration state of patient's intracellular sector. Its measurement can be carried out either by multiparametric laboratory analyser (indirect potentiometry) or delocalized biology analyser (direct potentiometry). The main problem is that for a same patient, these two analysers can give quite different results, hence inducing interpretation problems for clinician. Two one-week study periods comparing the variations in blood sodium levels produced by these automatic analysers were carried out in two intensive care units of Clermont-Ferrand University Hospital. During the second study period, a protocol for collecting blood samples was applied in order to improve the pre-analytical conditions. Between the two weeks of studies, the median of the differences in natremia was significantly reduced, going from 4mmol/L to 2mmol/L (p <0.001), as was the proportion of patients with large differences in sodium levels (strictly higher than 3mmol/L) going from 51% to 24.8% (p <0.001). The patients still presenting large variations in sodium had a median of proteins significantly lower than patients with deviations less than or equal to 3mmol/L: 58.1g/L against 62.25g/L respectively (p <0.001) leading to pseudo-hypernatremia (indirect potentiometry). Despite a significant reduction in differences linked to the application of good preanalytical practices, some patients nonetheless presented a major difference in natremia due to the difference of technique (variations in the lipidoprotein phase of the plasma of intensive care patients) and to the measurement uncertainties.

Order of draw of blood samples affect potassium results without K-EDTA contamination during routine workflow.

IntroductionA specific sequence is recommended for filling blood tubes during blood collection to prevent erroneous test results due to carryover of additives. However, requirement of this procedure is still debatable. This study was aimed to investigate the potassium ethylenediaminetetraacetic acid (K-EDTA) contamination in blood samples taken after a tube containing the additive during routine workflow. The study was also carried out to examine the effect of order of draw on potassium results, regardless of K-EDTA contamination.Materials and methodsIn 388 outpatients, to determine the probability of K-EDTA cross-contamination, blood was drawn sequentially into a serum tube, followed by a tube containing K-EDTA, and by another serum tube. In another 405 outpatients, to evaluate the effect of order of draw blood unrelated to K-EDTA contamination, two serum tube were successively collected. Potassium was measured on Cobas 6000 c501 analyser (Roche Diagnostic GmbH, Mannheim, Germany) by indirect ion selective electrode method.ResultsOf paired samples collected before and after a K-EDTA tube, 24% had a potassium difference of above 0.3 mmol/L. However, no EDTA contamination was detected in these samples as well as 95% confidence intervals (CI) of limits of agreement for calcium were within the allowable error limits based on reference change values. Interestingly, of blood samples drawn successively, 24% had also a difference greater than 0.3 mmol/L for potassium.ConclusionIncorrect order of draw using closed blood collection system does not cause K-EDTA contamination, even in routine workflow. However, regardless of K-EDTA contamination, order of draw has significant influence on the potassium results.

Effect of Hypoproteinemia on Electrolyte Measurement by Direct and Indirect Ion Selective Electrode Methods.

Objective The aim of this study was to see the effect of hypoproteinemia on electrolyte measurement by two different techniques, that is, direct ion selective electrode (ISE) and indirect ISE. Material and Method It was an observational study in which 90 serum samples with normal protein content (Group-1) were subjected to sodium (Na + ) and potassium (K + ) measurements by direct and indirect ISE methods. In the same way, 90 serum samples with total protein < 5 g/dL (Group-2) were subjected to Na + and K + measurements by direct and indirect ISE methods. Result In samples from Group-1 patients, average Na + was 138.1 ± 4.764 mmol/L by direct ISE method and 139.3 ± 3.887 mmol/L by indirect ISE method while average K + was 4.41 ± 0.644 mmol/L by direct ISE method and 4.40 ± 0.592 mmol/L by indirect ISE method. There was no statistically significant difference in Na + and K + values measured by different methods. In samples from Group-2 patients, measured value of Na + by direct ISE and indirect ISE was 134.57 ± 5.520 mmol/L and 138.64 ± 5.401 mmol/L, respectively. Difference between these two values was statistically significant with p -value of < 0.0001, but direct ISE and indirect ISE measured values of K + was 4.146 ± 0.9639 mmol/L and 4.186 ± 0.8989, respectively, with no significant difference. Conclusion Direct and indirect ISE methods are not comparable and showing significantly different results for Na + in case of hypoproteinemia. So, it is recommended that setups like intensive care unit or emergency department, where electrolyte values have significant treatment outcome, should follow direct ISE method and should compare its previous result with the same method. Both the methods should not be used interchangeably.

Preventing pseudohyponatremia: Intralipid®-based lipemia cutoffs for sodium are inappropriate

BackgroundPseudohyponatremia describes an artifactual decrease in plasma sodium result in samples with high proteins and/or lipids when measured by an indirect ion-selective electrode (ISE) method. We suspected that Intralipid®-based lipemia cutoffs are inappropriate for detecting interfering lipids in human samples and a major contributing factor to the existence of pseudohyponatremia. MethodsWe evaluated 2 approaches to derive a lipemia cutoff for sodium, one in which patient plasma samples were pooled and spiked to simulate hyperlipidemia using Intralipid® (commonly used approach by in-vitro diagnostics manufacturers), and another in which endogenous hyperlipidemic samples (n = 31) were measured by methods not affected by hyperlipidemia (i.e., direct ISE and post-ultracentrifugation indirect ISE). Triglycerides, lipemic index (L-index) and indirect ISE sodium concentrations of samples were measured on Roche Cobas® 8000 and direct ISE on Radiometer® ABL835 Flex analyzers. Endogenous hyperlipidemic samples were also ultracentrifuged on Beckman Coulter® Airfuge to clear excess lipids and re-analyzed for sodium by indirect ISE. ResultsWe discovered that Intralipid® is not an accurate emulation of the lipemic interference seen in pseudohyponatremia because it showed no effect up to the maximum level of lipemia tested (L-index = 2000). By contrast, endogenous hyperlipidemic samples demonstrated significant deviations in sodium concentration (≥4 mmol/l) when L-index approached or exceeded 700, and a strong positive correlation between L-index and the difference between the indirect and direct methods (i.e., extent of pseudohyponatremia). ConclusionsClinical laboratories should lower their tolerance for lipemia from the currently recommended L-index cutoff of 2000 on Roche Cobas 8000®. We recommend reflexing to direct ISE when L-index exceeds 700. Manufacturers and laboratories with other indirect ISE methods should evaluate the effect of lipid interference on their method using hyperlipidemic human samples not Intralipid®.

Serum sodium in relation to various domains of cognitive function in the elderly US population

BackgroundRecent evidence suggests that sodium imbalances may be associated with cognitive impairment; however, the association between specific domains of cognition remains unclear. This study examines the association between serum sodium levels and immediate and delayed verbal memory as measured by the CERAD Word Learning Test (CERAD WLT), executive function as measured by the Animal Fluency test (AFT), and sustained attention, working memory, and processing speed as measured by the Digit Symbol Substitution test (DSST) in the elderly population of the US aged 60 and older who participated in the 2011–2014 National Health and Nutrition Examination Surveys (n = 2,541).MethodsCognitive function tests were performed by trained interviewers and sodium levels were measured using indirect ion selective electrode methodology.ResultsAfter adjusting for all covariates, quintiles of CERAD WLT scores showed significant positive associations with log-transformed sodium levels (Immediate recall (IR) β = 4.25 (SE = 1.83, p-value 0.027); Delayed recall (DR) β = 6.54 (SE = 1.82, p-value 0.001)). Compared to normal sodium levels, hyponatremia was significantly associated with lower CERAD WLT-IR (β = -0.34, SE = 0.15, p-value 0.035) and CERAD WLT-DR scores (β -0.48, SE = 0.10, p-value < 0.001) and showed borderline significance with AFT scores (β = = -0.38, SE = 0.19, p-value 0.052). Hypernatremia did not show any significant relationships with cognitive test scores, compared to normal sodium levels.ConclusionsOur cross-sectional study showed that lower sodium levels were associated with cognitive change, especially regarding memory and executive function.

Risk factors related with high sodium intake among Malaysian adults: findings from the Malaysian Community Salt Survey (MyCoSS) 2017\u20132018

BackgroundHigh sodium intake was an established risk factor for stroke and cardiovascular diseases. The objective of this study was to investigate factors associated with high sodium intake based on 24-h urinary sodium excretion from the MyCoSS study.MethodsThe cross-sectional survey was conducted among adults aged 18 years and above in Malaysia. A multi-stage stratified sampling was used to represent nationally. Twenty-four-hour urine was collected from a total of 900 respondents. Indirect ion-selective electrode (ISE) method was used to measure sodium intake. Descriptive and logistic regression analysis was applied to determine factors associated with high sodium intake based on 24-h urinary sodium excretion.ResultsA total of 798 respondents (76% response rate) completed the 24-h urine collection process. Logistic regression revealed that high sodium intake associated with obese [aOR 2.611 (95% CI 1.519, 4.488)], male [aOR 2.436 (95% CI 1.473, 4.030)], having a waist circumference of > 90cm for adult males [aOR 2.260 ( 95% CI 1.020, 5.009) and >80cm for adult females [aOR 1.210 (95% CI 0.556, 2.631)], being a young adult [aOR 1.977 (95% CI 1.094, 3.574)], and living in urban areas [aOR 1.701 (95% CI 1.094, 2.645)].ConclusionAdults who are obese, have a large waist circumference, of male gender, living in urban areas, and belonging to the young adult age group were found to have higher sodium intake than other demographic groups. Hence, reduction of salt consumption among these high-risk groups should be emphasised to reduce the risk of cardiovascular diseases.

Pseudohyponatremia and falsely increased serum osmolal gap caused by paraprotein in a patient with severe metabolic acidosis – a case study

Abstract Introduction: The aim of the study is to present a case study of a 63-year-old male with pseudohyponatremia, falsely increased serum osmolal gap and severe metabolic acidosis. Material and Methods: Venous whole blood (direct sodium selective electrode measurement) and serum (indirect sodium selective electrode measurement) were used to measure sodium concentration. Serum cholesterol, triacylglycerides and total protein were measured to confirm pseudohyponatremia. Base excess in extracellular fluid and serum bicarbonate concentrations were employed as markers of metabolic acidosis. Serum protein electrophoresis and free light chain analysis were used for the detection of paraproteins. Results: Venous whole blood acid base analysis showed a pH of 7.171, negative base excess in extracellular fluid of – 18.6 mmol/L and sodium concentration of 140 mmol/L. Serum test measurement revealed serum sodium concentration of 130 mmol/L, osmolal gap of 24 mmol/kg, creatinine concentration of 702 µmol/L, HCO3- concentration of 6.1 mmol/L and total protein concentration of 134.9 g/L. Serum paraprotein IgG kappa with a concentration of 86 g/L and a serum free light chains kappa/lambda ratio of 223.5, along with the final diagnosis of multiple myeloma were detected. Toxic alcohol ingestion was considered, both methanol and ethylene glycol tests were negative. Conclusions: High paraprotein concentrations in serum may lead to pseudohyponatremia when measured by indirect ion selective electrodes. Multiple myeloma frequently leads to renal failure with metabolic acidosis.