Accurate assessment of the levels of serum electrolytes such as chloride, potassium, and sodium is vital for the clinical context, especially for subjects admitted to ICU (intensive care units). There are usually two methods that are used routinely. Central laboratory auto analyzers routinely asses serum electrolytes, however, the time needed is based on variable factors as time following sample collection, processing of sample, and analysis at laboratory. This delay can be harmful for critically ill subjects. However, on the contrary, ABG (arterial blood gas) analyzers are used widely in all ICUs (intensive care units) and emergency care as they allow rapid collection of data and therapeutics as ICU subjects can have non-specific symptoms and signs for electrolyte anomalies.1

Along with potassium and sodium, chloride is a main electrolyte seen in extracellular fluid and is vital to preserve the adequate fluid balance. Prevention of problems as dehydration, edema, and electrolyte imbalance in critical care units needs careful assessment of electrolyte balance. Chloride ions usually affect the tubular function, glomerular filtration rate, and renal blood flow. Metabolic acidosis is usually seen in subjects from critical care owing to various conditions as tissue hypoperfusion, infection, and organ malfunction. As chloride ions are needed in acid-base balance, they indirectly affect the respiratory function.2

It has been reported that electrolyte homeostasis is vital in normal functioning of functions of various organs and metabolic processes in the human resulting in electrolyte imbalance seen in various medical illness as diabetes mellitus and chronic renal failure along with few cancer subjects undergoing platinum-based chemotherapy. With introduction of blood gas analysers, it resulted in improved treatment of such subjects, especially in critically ill patients. The main benefit of these blood gas analyzers lies in the fact that they do not need centrifugation. Also, blood gas analyzers usually need only 2-3 minutes for completion of entire test.3

On the contrary, auto analyzers are used in biochemical studies and need the prior centrifugation of the samples before testing and the process need minimum 10 minutes. Additively to pre-analytical process, electrolyte assessment in autoanalyzer require time as they need advanced methods. In clinical labs, the autoanlyzer testing require minimum 90 minutes including sample amount, test methods, and centrifugation. Despite majority of the laboratories and doctors rely more on autoanalyzer results being more reliable and accurate, a high time needed restrict their use in managing critically ill subjects.4

The present prospective institution-based study was aimed to comparatively estimate the electrolyte levels as chloride, potassium, and sodium in subjects hospitalized in critical care as assessed by blood gas analyzer and automated biochemistry analysis and to assess agreement degree in these two. The study subjects were from Department of General Medicine and Critical care of the Institute. Verbal and written informed consent were taken from all the subjects before study participation.

The study assessed 60 paired samples from arteries and veins from critical care subjects where electrolytes were assessed on ABA (Automated Biochemistry Analyzer) and ABG (Arterial Blood Gas) analysis. The inclusion criteria for the study were subjects admitted at the critical care of the institute where venous blood sample analysis and arterial blood gas analysis was done for electrolyte testing done simultaneously and subjects were willing to participate. The exclusion criteria for the study were subjects having insufficient sample and improper sample timing.

For all the subjects, data gathered were demographics along with height in meters and weight in kgs which were then used to measure the BMI5 by division of weight (Kgs) with height (meter2). For blood pressure measurement, sphygmomanometer was used following standard measurement protocols.

For collection of sample and analysis of the electrolytes, 2ml of the arterial blood was collected for analysis by arterial blood gas analyzer following the principle of ion-selective electrode for electrolytes assessment by ABA (automated biochemistry analyser) following the principle of ion-selective electrode.

The present prospective institution-based study was aimed to comparatively estimate the electrolyte levels as chloride, potassium, and sodium in subjects hospitalized in critical care as assessed by blood gas analyzer and automated biochemistry analysis and to assess agreement degree in these two. The study assessed 60 paired samples from arteries and veins from critical care subjects where electrolytes were assessed on ABA (Automated Biochemistry Analyzer) and ABG (Arterial Blood Gas) analysis.

The present study assessed 60 subjects where majority if the study subjects were in the range of 61-70 years with 45% subjects followed by 27% subjects from 51-60, 12% in more than 70 years and 41-50 years both, and least 1% in 30-40 year. Considering the gender, there were 76% males and 24% female subjects in the study respectively. The study results also showed a strong agreement in two tools with p-value of 0.00001 for all three biochemical markers including sodium, potassium, and chloride levels. It was seen that for the comparison between serum electrolyte levels as assessed by ABG and ABA in study subjects, serum chloride levels in ABG and ABA analyzer was 100.77±6.63 and 100.45±6.39 mmol/L which was significantly higher with ABG analyzer compared to ABA analyzer with p-value of 0.04. However, a non-significant difference was seen in the value of potassium and sodium ion using either ABG or ABA analyzer with the p-values of 0.164 and 0.436 respectively (Table 2).

The study results showed that for the association of serum electrolytes in arterial blood gas analyzer and automated biochemistry analyzer in study subjects, a highly significant correlation was seen with chloride levels showing r- value of 0.923 and p-value of 0.00001. Concerning potassium, a highly significant correlation was seen in ABG and ABA with r and p-value of 0.977 and 0.0001 respectively. Similar significant correlation was seen in ABG and ABA concerning sodium ion with r and p-value of 0.971 and 0.0001 respectively (Table 2).

Table 1: Comparison between serum electrolyte levels as assessed by ABG and ABA in study subjects

Table 2: Association of serum electrolytes in arterial blood gas analyzer and automated biochemistry analyzer in study subjects

The present study assessed 60 paired samples from arteries and veins from critical care subjects where electrolytes were assessed on ABA (Automated Biochemistry Analyzer) and ABG (Arterial Blood Gas) analysis. The design conformed to the design in the previous studies of Jat NK et al6 in 2024 and Zhang JB et al7 in 2015 where study design similar to the present study was also adopted by the authors in their studies.

Concerning 60 subjects assessed in the study, majority of the study subjects were in the range of 61-70 years with 45% subjects followed by 27% subjects from 51-60, 12% in more than 70 years and 41-50 years both, and least 1% in 30-40 year. Considering the gender, there were 76% males and 24% female subjects in the study respectively. The study results also showed a strong agreement in two tools with p-value of 0.00001 for all three biochemical markers including sodium, potassium, and chloride levels. These data correlated with the findings from Shahmirzadi A et al8 in 2017 and Jain A et al9 in 2009 where authors assessed subjects with demographic data and electrolyte levels in their studies as in the present study.

The study results showed that for the comparison between serum electrolyte levels as assessed by ABG and ABA in study subjects, serum chloride levels in ABG and ABA analyzer was 100.77±6.63 and 100.45±6.39 mmol/L which was significantly higher with ABG analyzer compared to ABA analyzer with p-value of 0.04. However, a non-significant difference was seen in the value of potassium and sodium ion using either ABG or ABA analyzer with the p-values of 0.164 and 0.436 respectively. These results were in line with the previous studies of Gavala A et al10 in 2017 and Sanakal DB et al11 in 2016 where results for comparison between serum electrolyte levels as assessed by ABG and ABA comparable to the present study were also reported by the authors in their studies.

It was seen that for the association of serum electrolytes in arterial blood gas analyzer and automated biochemistry analyzer in study subjects, a highly significant correlation was seen with chloride levels showing r- value of 0.923 and p-value of 0.00001. Concerning potassium, a highly significant correlation was seen in ABG and ABA with r and p-value of 0.977 and 0.0001 respectively. Similar significant correlation was seen in ABG and ABA concerning sodium ion with r and p-value of 0.971 and 0.0001 respectively. These findings were in agreement with the results of Solak Y et al12 in 2016 and Mikkelsen S et al13 in 2015 where results reported by the authors for association of serum electrolytes in arterial blood gas analyzer and automated biochemistry analyzer were comparable to the results of the present study.

The present study, considering its limitations, concludes that there was no significant difference for the arterial blood gas analyzer and automated biochemistry analyzer measurements of chloride, potassium, and sodium. However, critically crucial decisions can be made by relying on the results attained from arterial blood gas analysis. 

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