Publications
and bibliography

Svenja Ravioli, Annemarie Edenhofner, Christoph Schwarz, Susanne Oswald, Gregor Lindner

>This publication, published in 2026, compares sodium and potassium measurements performed in the emergency department using point-of-care testing (POCT) and those obtained from the central laboratory. It is a retrospective single-center study conducted over a one-year period.
The authors emphasize that only a limited number of studies have evaluated discrepancies in electrolyte measurements, particularly sodium and potassium, despite the fact that these parameters are easily accessible on blood gas analyzers used for point-of-care testing. Nevertheless, these differences are already known.
The study compared 6,404 sodium measurements and 5,622 potassium measurements performed:
on the one hand, on whole blood samples in the emergency department using a Radiometer ABL90 blood gas analyzer;
on the other hand, in the central laboratory on plasma samples using a Roche analyzer.
Samples for point-of-care testing and laboratory analysis were collected less than one minute apart. Laboratory analyses were performed within two hours after the POCT measurement.
The main finding demonstrated a systematic difference between values obtained by point-of-care testing and those obtained in the central laboratory, with POCT values being generally higher than laboratory values. However, across more than 5,500 measurements, this discrepancy did not result in any major overall clinical impact on patient management.
The authors observed that sodium measurements showed only moderate agreement with laboratory results, whereas potassium measurements demonstrated better concordance.
For sodium, the difference between the two methods exceeded 4 mmol/L in 8.5% of cases and exceeded 8 mmol/L in 0.5% of cases. They also observed that the discrepancy between methods tended to increase at higher sodium concentrations.
For potassium, the difference exceeded 0.5 mmol/L in 4.5% of cases and exceeded 1 mmol/L in 1% of cases.
These discrepancies may nevertheless have important consequences for certain clinical situations, which constitutes one of the central points of the discussion.
In particular, in severe hyponatremia, management relies on the administration of hypertonic saline with repeated biological reassessments. Additional treatment is indicated if sodium levels fail to increase sufficiently, generally by approximately 5 mmol/L. The accuracy of sodium measurement is therefore essential in order to avoid undercorrection or overcorrection. Similar concerns apply to the management of hyperkalemia.
The authors therefore strongly recommend maintaining the same analytical method for electrolyte monitoring throughout the patient’s management.
Regarding the study limitations, the authors point out that this retrospective analysis does not allow precise identification of the causes of the observed discrepancies. Several hypotheses are discussed, including:
differences related to the electrodes used by the different analytical techniques;
the fact that point-of-care testing is performed on whole blood whereas laboratory measurements are performed on plasma;
potential biases related to hematocrit, protein concentration, lipemia, or hemolysis, which were not specifically collected in this study.
The authors also highlight the limited number of patients presenting with severe electrolyte disturbances, particularly severe hypernatremia.

Chafika Lasfer, Amal Lahib, Kariem Soliman, Shahinaz Gouda

The authors present a retrospective study involving 120 patients conducted over a three-month period in the emergency department of a hospital in Dubai. The aim was to compare, on a paired basis, sodium and potassium values obtained either by Point-of-Care Testing (POCT) using an Cobas b221 device or by the central laboratory on plasma, with a maximum sampling interval of 30 minutes between measurements. The authors emphasize that discrepancies in electrolyte measurements are a well-known and widely published issue, particularly for potassium and sodium. They also recall that, according to CLSI recommendations, acceptable bias should be ≤0.3 mmol/L for potassium and ≤3 mmol/L for sodium.

In this study, concordance for potassium showed an r value of 0.91 with a bias of +0.12 mmol/L, whereas sodium showed a correlation coefficient of 0.88 with a bias of -1.2 mmol/L.

The authors highlight the growing use of Point-of-Care Testing in emergency departments, as well as the various factors that may influence results, including calibration, analytical methodology, and electrode characteristics, particularly in situations of hyperkalemia or hyponatremia where clinical interpretation is especially critical.

Their conclusions indicate a slight overestimation of potassium values, in which hemolysis may play a role, as well as the nature of the electrodes used. Nevertheless, they point out that 97.5% of the compared values had no impact on clinical management.

Regarding sodium, the underestimation appears somewhat more significant, with 9.2% of normal sodium values underestimated by POCT. Il est cependant intéressant de noter que, malgré leur conclusion globalement favorable sur la concordance, l’observation du diagramme de Bland-Altman montre une dispersion relativement large des points, entre les limites de ±1,96 SD, allant d’environ -2 mmol/L à +6 mmol/L. The authors acknowledge several limitations of the study:

a relatively small cohort of 120 adult patients;

exclusion of pediatric populations, pregnant women, and oncology patients;

l’absence d’étude sur les conséquences cliniques potentielles en termes de traitement, de durée de séjour, d’effets secondaires ou de devenir des patients.

A brief analysis of turnaround time differences was also performed and showed a relatively small advantage of approximately 10 minutes. However, it should be noted that the laboratory involved appeared to provide exceptionally rapid result reporting. The authors’ practical conclusion is that any extreme value — potassium above 5.5 mmol/L or sodium below 130 mmol/L — should systematically prompt confirmation by central laboratory testing. Finally, as observed in the other publication analyzed in this literature review, the authors do not truly address the distinction between direct and indirect potentiometry, despite mentioning methodological and electrode-related differences.