Direct Ion-selective Electrode Research Articles

Hyponatremia in Critically Ill Patients Due to Continuous Venovenous Hemofiltration With Diluted Sodium Citrate.

Continuous venovenous hemofiltration (CVVH) is frequently performed in critically ill patients using diluted citrate for regional anticoagulation. The impact of this renal replacement strategy on plasma sodium has not been evaluated yet. Our aim was therefore to assess the period prevalence of hyponatremia (sodium <135 mmol/L) during CVVH and discuss possible underlying mechanisms. After 48 hours of treatment, 70% of the 27 oligo-anuric critically ill patients were hyponatremic, despite the use of dialysis fluid bags (Regiocit 18/0, Phoxilium by Baxter, Deerfield, IL, and Multibic K2 by Fresenius Medical Care AG & Co. KGaA, Bad Homburg, Germany) with sodium content of 140 mmol/L. Indeed, sodium decreased from 142 ± 7 to 135 ± 3 mmol/L, p < 0.001. Sodium concentrations of employed dialysis bags were confirmed using ion chromatography. However, ionized sodium of Regiocit measured with a direct-ion selective electrode (ISE) resulted lower (~118 mmol/L), suggesting the presence of sodium-to-citrate complexes. Possible mechanisms explaining the hyponatremia development could therefore include: i) plasma water dilution; ii) a reduced Gibbs-Donnan effect, given the low albumin concentration (2.6 ± 0.8 g/dl) of our critically ill patients; iii) a negative sodium balance due to the loss of sodium-to-citrate complexes across the filter. The clinical implications of the described hyponatremia and the different contributions of the hypothesized mechanisms need to be addressed in future studies.

Pseudohypobicarbonatemia Associated with Profound Hypertriglyceridemia

A case is presented of falsely low serum bicarbonate levels with normal arterial blood gas bicarbonate levels in a patient with high triglyceride (TG) levels. This false phenomenon is explained by the presence of high triglyceride levels. Most laboratories use an enzymatic/photometric or indirect ion-selective electrode method to measure bicarbonate. Hyperlipidemia interferes with photometric analysis due to its light scattering effect. An ABG analyser employs a direct ion-selective electrode method that is free from the errors of a photometric analyser. Currently, several methods are available to eliminate the interference of lipemia and allow accurate measurement of biological quantities. The clinical laboratory must establish a protocol for handling lipemic samples according to the biological quantity to be tested.

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.

Sweat Rate, Sweat Sodium Losses, and Body Composition in Professional Male Soccer Players in Southwest Colombia.

Background and Objective: Dehydration and hyperhydration impact athletes' performance. Exploring the fluid balance concerning body composition might help estimate individual hydration requirements. This area of research, particularly regarding sodium losses, has been relatively understudied. We evaluated the sweat rate (SR), sweat sodium losses, and their relationship with body composition in professional soccer players in Cali, Colombia. Materials and Methods: Thirty-two male players, aged 24.3 (±5.2) years, from the Colombian main soccer league, underwent high-intensity training at 32 °C (with a relative humidity of 79%). The outcome variables included SR, calculated using weight loss and fluid intake; forearm sweat sodium concentration (FSCC), measured through the direct ion-selective electrode method; and estimated the predicted whole sweat sodium loss (PWSSL) in mmol. Predictor variables (body mass, fat, and muscle masses) were estimated using the Deborah Kerr anthropometry method. The association between predictors and outcomes was assessed using linear regression. Results: The mean FSCC, PWSSL, and SR were 26.7 ± 11.3 mmol/L, 43 ± 15.9 mmol/L, and 1.7 ± 0.5 L/h, respectively. Body mass positively predicted FSCC in unadjusted and age/fat-mass-adjusted models [Beta 1.28, 95% confidence interval (CI) 0.39-2.18, p = 0.006], and continued related to FSCC after adjustment for muscle mass with marginal significance [Beta 0.85, 95% CI -0.02 to 1.73, p = 0.056]. Muscle mass was associated with the PWSSL in unadjusted and age/fat-mass-adjusted models [Beta 2.42, 95% CI 0.58-4.26, p = 0.012] and sustained an association with marginal statistical significance after adjustment for body mass [Beta 1.86, 95% CI -0.35 to 4.09, p = 0.097]. Conclusions: Under hot tropical weather conditions, FSCC was relatively low among the players. Body mass was better associated with the FSSC, and muscle mass better related to the PWSSL. Body and muscle masses could be regarded as potential factors to be explored in the estimation of individual sodium needs. However, further studies are required to validate and contrast our findings.

Monitoring of ionized magnesium in hemodialysis patients: A useful tool to allow a personalized prescription of dialysate composition

Background and aimsThe dialysate magnesium (Mg) concentration is a major determinant of Mg balance in hemodialysis. This study aimed to assess the systemic variations of total (tMg) and ionized Mg (iMg) during a dialysis session using acetate or citrate fluids and 0.5 or 0.75 mM Mg. Materials and methods134 patients in maintenance hemodialysis were assigned to a dialysis session with 4 different dialysates: acetate fluid with 0.5 mM Mg (1) or 0.75 mM Mg (2), citrate fluid with 0.5 mM Mg (3) or 0.75 mM Mg (4). Ionized form was measured by direct ion-selective electrode. ResultsA Mg loss was observed in both acetate (0.12 and 0.08 mmol/L) and citrate (0.13 and 0.14 mmol/L for tMg and iMg, respectively) fluid groups containing 0.5 mM Mg. The use of acetate and citrate dialysates with 0.75 mM Mg led to a significant median intra-dialytic increase of 0.15 and 0.08 mmol/L for tMg, respectively. A significant augmentation in iMg concentration with acetate (0.11 mmol/L) but not with citrate dialysate (0.02 mmol/L) was observed. ConclusionWhile a dialysate Mg concentration at 0.5 mM leads to a negative balance, increasing the concentration to 0.75 mM significantly raises post-dialysis circulating Mg. Monitoring of iMg should allow a personalized prescription in dialysate Mg.

The Stability of Analytes of Ionized Magnesium Concentration and Its Reference Range in Healthy Volunteers.

This study aimed to determine the stability of refrigerated analytes of iMg concentration at different time intervals and to establish iMg reference range in a cohort of healthy Omani volunteers (≥18 years). The concentrations of iMg were measured using the direct ion-selective electrode technique. Pearson's and Lin's concordance correlation coefficients along with the Bland-Altman plot were used to assess the levels of agreement between iMg concentrations of fresh and refrigerated blood samples at different time intervals. The study included 167 volunteers (51% females) with a median age of 21 (range: 20-25) years. The median, 2.5th, and 97.5th percentiles for fresh iMg reference ranges were 0.55, 0.47, and 0.68 mmol/L, respectively. The overall agreement between the fresh and refrigerated iMg concentrations was poor (rho-c = 0.51; p < 0.001). However, according to Altman's definition, iMg concentrations of the refrigerated samples for a period of ≤1 h had an excellent correlation with the fresh iMg concentrations (Lin's rho-c = 0.80), with a small average bias difference of 0.009 (95%CI; -0.025-0.043). A cut-off refrigeration period within ≤1 h at 2-8 °C can be considered an alternate time frame for the gold standard measurement (fresh or within 0.5 h).

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.

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.

MO649: Monitoring of Ionized Magnesium in Haemodialysis Patients: A Useful Tool to Allow a Personalized Prescription of Dialysate Composition

Abstract BACKGROUND AND AIMS In healthy subjects, normal values of magnesium (Mg) are in the range 0.75–0.95 mmol/L. In the circulation, 65–70% of the Mg is present in the free, ionized and dialyzable form (i.e. 0.45– 0.60 mmol/L), 20% is bound to proteins and 15% is complexed. In chronic kidney disease (CKD) dialysis patients, the dialysate Mg concentration is a major determinant of Mg balance. The aim of this study was to assess the systemic variations of ionized Mg (iMg), as well as that of ionized calcium (iCa), before and after a dialysis session. METHOD A total of 121 dialysis patients [median age = 70 (62.5–78.2) years; 74 male/46 female] in maintenance haemodialysis three times per week, for at least 6 months and with no residual function, were included. Patients were assigned to a single dialysis session with either control fluid (group 1: 3 mM acetate, 1.5 mM Ca, 0.5 mM Mg), or citrate dialysis fluid containing 0.5 mM Mg (group 2: 0.8 mM citrate, 0.3 mM acetate, 1.65 mM Ca) or 0.75 mM Mg (group 3: 0.8 mM citrate, 0.3 mM acetate, 1.65 mM Ca). Blood samples were drawn before and after the midweek dialysis sessions as part of the routine patient follow-up and quality assurance process. iMg and iCa concentrations were measured by direct ion-selective electrode on Nova Stat Profile Prime Plus® (Nova Biomedical). Total Mg (tMg) and Ca (tCa) were assessed by colorimetric method c702/Cobas 8000 analyzer (Roche). Dialytic balance was assessed by the median intra-dialytic difference between pre-dialysis and post-dialysis. RESULTS The use of all types of dialysates (whatever their composition was) was associated with a calcium load during the session (Table). In addition, an Mg loss was observed in both control and citrate dialysis fluid groups containing 0.5 mM Mg. The dialysis session induced a significant decrease in iMg (13 and 22% in group1 and group 2 respectively). By contrast, the use of citrate dialysis fluid with 0.75 mM Mg led to a positive balance with a median intra-dialytic increase of 0.08 and 0.02 mmol/L in tMg and iMg respectively (Table), corresponding to a median increase of 8 and 3% in tMg and iMg respectively. CONCLUSION The iMg fraction represents 70% of tMg in CKD stage 5D patients. While a dialysate Mg concentration at 0.5 mM leads to a negative balance, increasing the concentration to 0.75 mM significantly raises post-dialysis circulating Mg levels in these patients. Therefore, monitoring of iMg should allow a personalized prescription in dialysate Mg composition.

T120 Comparison between serum calcium levels measured using direct ion-selective electrodes and photometric method in automated analyzers

T120 Comparison between serum calcium levels measured using direct ion-selective electrodes and photometric method in automated analyzers

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.

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.

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.

The effect of haemolysis on the direct and indirect ion selective electrode measurement of sodium.

We compared the effect of haemolysis in sodium measurement using indirect and direct ion-selective electrodes to test the hypothesis that haemolytic effect on sodium would be greater with indirect ion-selective electrode due to electrolyte exclusion effect from released intracellular proteins. Plasma lithium heparin samples (n = 36) from four volunteers were prepared to give a range of haemolytic indices (H-indices). Samples were analysed for sodium by indirect ion-selective electrode, H-index and total protein on an Abbott Architect c16000 and sodium by direct ion-selective electrode on a Siemens RAPIDPoint 500. Percentage changes in sodium in paired direct and indirect ion-selective electrode values were compared. Abbott H-index, which represents haemoglobin concentration in g/L, correlated with percentage negative change in sodium by direct ion-selective electrode (ρ 0.995, P < 0.001) and indirect ion-selective electrode (ρ 0.991, P < 0.001). Percentage negative change was less when sodium was measured by direct ion-selective electrode compared to indirect ion-selective electrode (Wilcoxon signed-rank Z = 3.46, P = 0.01). The difference in percentage change in sodium between direct ion-selective electrode and indirect ion-selective electrode correlated with total protein (ρ 0.751, P < 0.001). The negative bias in sodium results exceeded the reference change value of 2.2% at an H-index of 8.31 for indirect ion-selective electrode and 9.26 for direct ion-selective electrode. Haemolysis causes negative influence with sodium measured by both indirect and direct ion-selective electrode due to a dilutional hyponatremia. The additional interference in indirect ion-selective electrode is due to the electrolyte exclusion effect but this is unlikely to be clinically significant as it is small in magnitude.

A study comparing values of serum sodium estimated by colorimetric kit method with those obtained by direct and indirect ion selective electrode methods

Introduction: Electrolyte abnormalities are known to cause significant morbidity and mortality, when it is not detected. Dyselectrolytemias are usually treatable. Hyponatremia is a common manifestation encountered in the elderly. The rural health care facilities may not have well equipped laboratories. Therefore, this study intended to look for the possibility of establishing a screening technique that can help detect hyponatremia in such centres. Materials and Methods: Serum sodium levels were estimated in 120 samples using direct, indirect ISE and colorimeter. Statistical analysis was done using SPSS version 17, NCSS 11 and MINITAB 18 software. A p value< 0> Results: A simple linear regression analysis was done and a regression equation was derived for sodium levels while comparing between the instruments. The Bland Altman analysis gave an agreement limit of 95% between the instruments which is well within the CLIA suggested target value of ±4 mmol/L in the hyponatremic and normonatremic range. Conclusion: The derived regression equation calculates a predicted value for direct and Indirect ISE using the values obtained on the colorimeter making it comparable on all the three instruments in the hyponatremic and normonatremic ranges. The colorimetric method can be used as a cost effective screening technique to identify the hyponatremic elderly for whom a tertiary hospital may not be accessible, thus facilitating early intervention. Keywords: Serum sodium, Direct ISE, Indirect ISE, Colorimetry, Hyponatremia.

Comparison between Serum Calcium Levels Measured Using Direct Ion-selective Electrodes and Photometric Method in Automated Analyzers

Comparison between Serum Calcium Levels Measured Using Direct Ion-selective Electrodes and Photometric Method in Automated Analyzers

Discrepancies in Electrolyte Measurements by Direct and Indirect Ion Selective Electrodes due to Interferences by Proteins and Lipids.

Objectives We aim to report the simultaneous effect of different protein and lipid concentrations on sodium (Na + ) and potassium (K + ) measurement by direct and indirect ion selective electrodes (dISE and iISE) in patient samples. Materials and Methods Na + and K + were measured in 195 serum samples received in the laboratory using iISE by Roche Modular P800 autoanalyzer and using dISE by XI-921 ver. 6.0 Caretium electrolyte analyzer. Serum total protein (TP), cholesterol (Chol), and triglycerides (TG) were measured using conventional photometric methods on Roche Modular P800 autoanalyzer. Differences for each pair of results for Na + (Diff_Na + = [Na + dISE– Na + iISE ]) and K + (Diff_K + = [K + dISE– K + iISE ]) were calculated. Patient subgroups with high, normal, or low TP (< 5, 5–7.9, or ≥ 8 g/dL), Chol (< 150, 150–299, or ≥300 mg/dL), or TG (< 150, 150–299, or ≥300 mg/dL) were compared using analysis of variance. Note that 95% confidence interval of Diff_Na + and Diff_K + were calculated to see the number of samples showing clinically significant differences. Results Diff_Na + ( p = 0.007) and Diff_K + ( p = 0.002) were found significant between samples with normal and high TP. However, effect of TG was not significant. Chol concentration affected Diff_Na + significantly between low versus normal ( p = 0.002), and high versus normal ( p = 0.031) Chol groups. Diff_K + was significant ( p = 0.009) between low versus normal Chol. Clinically relevant disagreement of ≥|5| mmol/L for Na + was observed in high percentage of samples including all subcategories; however, for K + only 3.6% of the total samples showed disagreement of ≥ |0.5| mmol/L. A multivariate regression equation based on fit regression model was also derived. Conclusion Summarily, interchangeable use of electrolyte results from dISE and iISE is not advisable, especially in a setting of hyperproteinemia (≥8 g/dL) or hypercholesterolemia (≥300 mg/dL); more so for Na + .