How to Solve the Underestimated Problem of Overestimated Sodium Results in the Hypoproteinemic Patient

Interference in Ion-Selective Electrodes Due to Proteins and Lipids

BACKGROUND

Ion-selective electrodes (ISE) have become the mainstay of electrolyte measurements in the clinical laboratory. In most automated analyzers used in large diagnostic laboratories, indirect ISE (iISE) -based electrolyte estimation is done; whereas direct ISE (dISE) -based equipment are mostly used in blood gas analyzers and in the point-of-care (PoC) setting.

CONTENT

Both the techniques, iISE as well as dISE, are scientifically robust; however, the results are often not interchangeable. Discrepancy happens between the two commonly due to interferences that affect the two measuring principles differently. Over the last decade, several studies have reported discrepancies between dISE and iISE arising due to abnormal protein and lipid contents in the sample.

SUMMARY

The present review endeavors to consolidate the knowledge accumulated in relation to interferences due to abnormal protein and lipid contents in sample with the principal focus resting on probable solutions thereof.

Which laboratory technique is used for the blood sodium analysis in clinical research? A systematic review

BACKGROUND

Circulating sodium is analyzed by flame spectrometry and indirect or direct potentiometry. The differences between estimates returned by the three techniques are often relevant. It is unknown whether peer-reviewed international publications focusing on this parameter provide information about the technique. Objectives of the study were to ascertain if information about the employed technique is provided.

CONTENT

A search in the National Library of Medicine for articles whose title contains "hyponatr[a]emia" was performed. We restricted the search to clinical reports including 10 or more humans published in the 2013-2015 and 2017-2019 periods. Authors of papers not reporting the technique were contacted to obtain this information. The study design and journal quartile ranking of each article were also evaluated.

SUMMARY

For the final analysis, we included 361 articles (2013-2015, n=169; 2017-2019, n=192). Information about the laboratory technique was given in 61(17%) articles. Thanks to our inquiry, we collected this information for 116(32%) further reports. Indirect potentiometry was the most frequently used technique, followed by direct potentiometry. Spectrometry was used in a small minority of studies. Study design, journal ranking and study period did not modulate the mentioned frequency.

OUTLOOK

Most articles focusing on hyponatremia do not provide information on the laboratory technique. This parameter is nowadays analyzed by indirect or, less frequently, direct potentiometry. The figures are similar for high and low impact factor journals and for the 2013-2015 and the 2017-2019 periods. Many authors, reviewers and editors likely assume that the results of this parameter are not influenced by the technique.

A Novel Uremic Score Reflecting Accumulation of Specific Uremic Toxins More Precisely Predicts One-Year Mortality after Hemodialysis Commencement: A Retrospective Cohort Study

Uremic toxins (UTs) generally accumulate in patients developing end-stage renal disease (ESRD). Although some kinds of UTs cause early death after starting hemodialysis (HD), it remains unknown whether the degree of excessive accumulation of various UTs is associated with worsening of prognosis. We retrospectively conducted this cohort study consisting of adult patients developing ESRD who initiated HD at the National Center for Global Health and Medicine from 2010 to 2019. We created a new uremic score, which was defined as the aggregate score of the following variables reflecting uremic state: elevated blood urea nitrogen, β2-microglobulin, and anion gap before starting HD. The primary outcome was early mortality within 1-year after HD commencement. The hazard ratio (HR) and 95% confidence interval (CI) for a one-point increase in uremic score was calculated with Cox proportional hazard models adjusted by baseline conditions. We included 230 participants, 16 of whom experienced the primary outcome of early mortality after HD commencement. Uremic score was significantly associated with the primary outcome (crude HR: 1.91, 95% CI 1.16–3.14; adjusted HR: 4.19, 95% CI 1.79–9.78). Our novel uremic score, reflecting accumulation of specific UTs, more precisely predicts early mortality after HD commencement.

Critical evaluation of equations for serum osmolality: Proposals for effective clinical utility

BACKGROUND

Many studies have assessed the predictive accuracy of serum osmolality equations. Different approaches for selecting a usable equation were compared using thirty published equations and patient data from a regional hospital laboratory.

METHODS

Laboratory records were extracted with same-sample results for measured serum osmolality, sodium, potassium, urea and glucose analysed in a regional hospital laboratory between 1/1/2017-31/12/2018. Differences were analysed using Passing-Bablok and difference (Bland-Altman) analysis. Three approaches were compared: the shotgun approach, adjusting for bias, and deriving a novel equation using multivariate analysis. The criteria for success included bias ≤0.7%, a 230 - 400 mOsm/kg range, and osmolal gap (OG) 95% reference limits within ±10 mOsm/kg.

RESULTS

The majority of equations produced proportionally negative-biased results. The shotgun approach identified two equations (EQ19, EQ6) with bias ≤0.7% but unworkable OG reference limits. The bias adjustment approach produced several equations with bias ≤ 0.7% and OG reference limits within or equivalent to ±10 mOsm/kg. A novel equation generated by us (1.89Na⁺ + 1.71 K⁺ + 1.08 Urea + 1.08 Glucose + 13.7) improved with the adjustment of bias and was not superior to the adjusted published equations.

CONCLUSION

Few published equations are immediately usable. Adjustment of bias derives several usable equations of which the best had OG ranges <20 mOsm/kg. We conclude that adjustment of bias can generate equations of equal or superior performance to that of novel equations.

154 compared to 54 mmol per liter of sodium in intravenous maintenance fluid therapy for adult patients undergoing major thoracic surgery (TOPMAST): a single-center randomized controlled double-blind trial

PURPOSE

To determine the effects of the sodium content of maintenance fluid therapy on cumulative fluid balance and electrolyte disorders.

METHODS

We performed a randomized controlled trial of adults undergoing major thoracic surgery, randomly assigned (1:1) to receive maintenance fluids containing 154 mmol/L (Na154) or 54 mmol/L (Na54) of sodium from the start of surgery until their discharge from the ICU, the occurrence of a serious adverse event or the third postoperative day at the latest. Investigators, caregivers and patients were blinded to the treatment. Primary outcome was cumulative fluid balance. Electrolyte disturbances were assessed as secondary endpoints, different adverse events and physiological markers as safety and exploratory endpoints.

FINDINGS

We randomly assigned 70 patients; primary outcome data were available for 33 and 34 patients in the Na54 and Na154 treatment arms, respectively. Estimated cumulative fluid balance at 72 h was 1369 mL (95% CI 601-2137) more positive in the Na154 arm (p < 0.001), despite comparable non-study fluid sources. Hyponatremia < 135 mmol/L was encountered in four patients (11.8%) under Na54 compared to none under Na154 (p = 0.04), but there was no significantly more hyponatremia < 130 mmol/L (1 versus 0; p = 0.31). There was more hyperchloremia > 109 mmol/L under Na154 (24/35 patients, 68.6%) than under Na54 (4/34 patients, 11.8%) (p < 0.001). The treating clinicians discontinued the study due to clinical or radiographic fluid overload in six patients receiving Na154 compared to one patient under Na54 (excess risk 14.2%; 95% CI - 0.2-30.4%, p = 0.05).

CONCLUSIONS

In adult surgical patients, sodium-rich maintenance solutions were associated with a more positive cumulative fluid balance and hyperchloremia; hypotonic fluids were associated with mild and asymptomatic hyponatremia.

Management of electrolyte disorders: also the method matters!

Introduction: For the last few decades, electrolyte determinations in plasma or serum are carried out by reliable potentiometric methods. In recent years, a marked technical evolution has taken place, where the clinical analysis of common analytes (e.g. electrolytes) is partly moving from centralised clinical core laboratories to near-patient point-of-care testing. Methods: As the measuring principle used by point-of-care testing markedly differs from the one used in core laboratories, sodium results are not always interchangeable in critically ill patients due to the different sensitivity of the analytical methods for the electrolyte exclusion effect. Results: This effect mainly occurs in patients with decreased plasma protein values. The observed differences in generated test results might significantly affect the judgment and the treatment of electrolyte disturbances. As technical solutions are not likely to occur in the near future, clinicians and laboratorians should be well aware of this growing problem. Mathematical correction of the sodium results for plasma protein concentration may resolve the problem to a certain extent. Discussion: Although electrolyte determinations are generally very reliable, analytical interferences can occur for sodium rarely, mainly due to contamination by surfactants, benzalkonium in particular. For potassium, the major problem is hemolysis. To a lesser extent, leukocyte lysis and thrombocytopenia may also interfere. For chloride determination, the selectivity of the electrodes used is not ideal. Occasionally, false positive signals can be observed in presence of interfering ions (e.g. bromide).

Interchangeability of Sodium and Potassium Result Values of Arterial Blood Gas with Laboratory Analyzer: Narrative Review

The major extracellular electrolytes, sodium, and potassium are often requested together and form a large percentage of the requested tests in routine clinical chemistry laboratories. Two types of devices that use direct and indirect ion-selective electrode (ISE) methods are used in hospitals for electrolyte measurements: blood gas analyzers (BGA), which use direct ISE technology, and the indirect ISE method, which is often used in a central-laboratory autoanalyzer (AA).

We aimed to summarize the current scientific knowledge based on whether the electrolyte test results, using Na and K test results obtained with BGA and an AA, can be used interchangeably.

We searched Medline (PubMed), Google Scholar, and Web of Science up to 31st March 2018. In addition, references of the included studies were also examined.

Fourteen studies with a risk of bias were included in the analysis. Limits of agreement differences were variable among BGA and AA sodium and potassium test results in clinical practice.

The results of both BGA and AA measures should not be used interchangeably under the assumption that they are equivalent to each other.

Point-of-Care Versus Central Laboratory Measurements of Hemoglobin, Hematocrit, Glucose, Bicarbonate and Electrolytes: A Prospective Observational Study in Critically Ill Patients

Introduction

Rapid detection of abnormal biological values using point-of-care (POC) testing allows clinicians to promptly initiate therapy; however, there are concerns regarding the reliability of POC measurements. We investigated the agreement between the latest generation blood gas analyzer and central laboratory measurements of electrolytes, bicarbonate, hemoglobin, hematocrit, and glucose.

Methods

314 paired samples were collected prospectively from 51 critically ill patients. All samples were drawn simultaneously in the morning from an arterial line. BD Vacutainer tubes were analyzed in the central laboratory using Beckman Coulter analyzers (AU 5800 and DxH 800). BD Preset 3 ml heparinized-syringes were analyzed immediately in the ICU using the POC Siemens RAPIDPoint 500 blood gas system. We used CLIA proficiency testing criteria to define acceptable analytical performance and interchangeability.

Results

Biases, limits of agreement (±1.96 SD) and coefficients of correlation were respectively: 1.3 (-2.2 to 4.8 mmol/L, r = 0.936) for sodium; 0.2 (-0.2 to 0.6 mmol/L, r = 0.944) for potassium; -0.9 (-3.7 to 2 mmol/L, r = 0.967) for chloride; 0.8 (-1.9 to 3.4 mmol/L, r = 0.968) for bicarbonate; -11 (-30 to 9 mg/dL, r = 0.972) for glucose; -0.8 (-1.4 to -0.2 g/dL, r = 0.985) for hemoglobin; and -1.1 (-2.9 to 0.7%, r = 0.981) for hematocrit. All differences were below CLIA cut-off values, except for hemoglobin.

Conclusions

Compared to central Laboratory analyzers, the POC Siemens RAPIDPoint 500 blood gas system satisfied the CLIA criteria of interchangeability for all tested parameters, except for hemoglobin. These results are warranted for our own procedures and devices. Bearing these restrictions, we recommend clinicians to initiate an appropriate therapy based on POC testing without awaiting a control measurement.