Key words : Point-of-care, Pretransplant laboratory analyses, Renal transplantation

Introduction
Maintaining hemostasis and electrolyte balance is of utmost importance in pediatric renal transplant patients. The proper functioning of organs involved in homeostasis relies on a well-regulated fluid-electrolyte balance.^1,2 Therefore, it is crucial to swiftly obtain laboratory results in pediatric renal transplant recipients, particularly immediately before the transplant procedure.

Blood-gas analyzers offer rapid measurement of electrolyte, hemoglobin, and hematocrit levels within 2 to 3 minutes, whereas laboratory automatic analyzers require approximately 2 hours for the same measurements. Although the results obtained from laboratory automatic analyzers are considered reliable, their long turnaround time limits their utility in critical interventions.³ Several studies have investigated the reliability of results from blood-gas analyzers compared with laboratory automatic analyzers for measurement of electrolytes, hemoglobin, and hematocrit, but the findings have been inconsistent. Although some studies have reported the reliability of results from blood-gas analyzers, others have found results to be unreliable.^4-9 These conflicting results highlight the need for further investigation.

Moreover, the reduced blood sample requirement for blood-gas analysis compared with automatic laboratory analysis is a significant consideration. This is particularly crucial when dealing with the challenges of obtaining blood samples from children. Obtaining rapid and accurate results for electrolyte levels and hemoglobin values using blood-gas analysis with a smaller blood sample is highly valuable. Therefore, the primary objective of our study was to conduct a comparative analysis of hemoglobin and electrolyte measurements obtained through blood-gas analysis versus standard laboratory tests in the specific context of pediatric renal transplant, with a specific emphasis on the immediate pretransplant period.

Materials and Methods
Our retrospective single-center study focused on pediatric renal transplant candidates. We aimed to analyze the results of patients under the age of 18 who had undergone simultaneous venous blood-gas analysis, complete blood count, and electrolyte panel before renal transplant within the past 2 years. The Institutional Review Board of Baskent University Hospital approved this observational study (ethics committee no. KA 24/154). Given the retrospective design of the study, the requirement for informed consent was waived.

Laboratory analyses
All samples underwent processing and analysis in the laboratory setting. Venous blood-gas samples were collected using sterile blood gas injectors containing dry lithium heparin for blood-gas analysis. After arrival to the laboratory, the collected samples were promptly analyzed using the ABL-800 Blood Gas Analyzer (manufactured by Radiometer). Electrolyte levels were determined using the direct ion selective electrode method on the blood-gas analyzer. In terms of biochemical measurements, sodium and potassium levels were analyzed with the ion selective electrode method on the Alinity C Analyzer (manufactured by Abbott). Hemoglobin and hematocrit levels were measured using the Alinity hq otoanalyzer (Abbott).

Statistical analyses
We reviewed medical records of included patients and compared simultaneous measurements of hemoglobin, sodium, and potassium from a blood-gas analyzer versus a laboratory automatic analyzer. We first compared results from the blood-gas analyzer versus the laboratory automatic analyzer with the Bland Altman method. The Bland Altman method was developed as an alternative to correlation analysis.¹⁰ In this method, the average of the compared method values is taken, the differences between the values are calculated, 95% CIs are determined, and a graph is drawn.¹¹ After we viewed the distribution of the difference between measurements with the Brand Altman graph, we used independent sample t tests and Mann-Whitney U tests to check for significant differences between the 2 measurements.

We then evaluated the intermeasurement agreement in more detail by using the Cohen kappa statistic. The Cohen kappa statistic determines whether the degree of agreement between 2 raters is higher than expected by chance.¹² If the kappa value is calculated as less than zero, there is poorer agreement than chance; if the value is between 0.01 and 0.20, there is insignificant agreement; if the value is between 0.21 and 0.40, there is poor agreement; if between 0.41 and 0.60, there is a moderate level of agreement; if between 0.61 and 0.80, there is a good level of agreement; and if between 0.81 and 1.00, there is very good level of agreement.¹³

We used IBM SPSS Statistics 25.0 package program for statistical analyses. P ≤ .05 was considered significant.

Results
Table 1 includes demographic information of the 26 pediatric patients who received a renal transplant for last 2 years. The mean age at transplant was 10.5 ± 5.1 years; 88.5% of the patients had transplants from living donors. The most frequently observed primary disease was glomerular diseases (23.1%), followed by congenital anomalies and tubulointerstitial diseases with equal percentages (19.2%).

We compared measurements of sodium, hemoglobin, and potassium from the blood-gas analyzer versus the laboratory automatic analyzer graphically (Figure 1). Measurements of sodium, potassium and hemoglobin values between analyzers were comparable. Table 2 shows comparison of differences between measurements of sodium, potassium, and hemoglobin in 26 patients using blood-gas test versus laboratory automatic analyzer. The mean differences between the blood-gas analyzer and the venous laboratory analyzer (95% CI) were as follows: 0.11 g/dL for hemoglobin (-0.27 to 0.05 g/dL; P > .05), 0.39 mEq/L for sodium (-0.58 to 1.35 mEq/L; P > .05), and 0.00 mEq/L for potassium (-0.25 to 0.25 mEq/L; P > .05), in parallel with Bland-Altman analyses. No significant differences were shown between sodium, potassium, and hemoglobin measurements (P > .05). Our evaluation did not take into account calcium measurements, as it would be improper to. compare calcium levels obtained from the automated laboratory with the ionized calcium values derived from blood-gas analysis..

In evaluations made in accordance with Cohen kappa values, the highest agreement was obtained with sodium measurements. Blood-gas and laboratory measurement values ranged between 129 and 147, and a kappa value of 0.275 was obtained. For potassium, measurement results were between 3 and 6, with calculated kappa of 0.042. Hemoglobin measurements were between 7 and 12, but agreement could not be achieved, showing a kappa value of 0.055.

Discussion
Our study aimed to address the ongoing debate regarding the use of blood-gas measurements versus automated laboratory measurements in children, specifically in pediatric renal transplant recipients during the immediate pretransplant period.^4,14 We specifically focused on whether measurements of sodium, potassium, and hemoglobin obtained with a blood-gas analyzer were comparable with measurements obtained with an automated laboratory analyzer. Our findings indicated agreement between the measurements obtained from both methods, suggesting that rapid blood-gas analysis can provide reliable and accurate results for sodium, potassium, and hemoglobin measurements in pediatric renal transplant recipients.

Our study has substantial implications for the management of pediatric transplant patients, as anemia and electrolyte disorders have important prognostic implications in this population. With the demonstration of concordance between rapid blood-gas values and automatic laboratory values, we provide evidence for the reliability of blood-gas analysis in assessing these parameters. This finding enables clinicians to make timely and accurate clinical decisions based on these measurements. However, it is crucial to consider findings from other studies conducted in pediatric liver transplant patients. For example, Morris and colleagues reported inadequate reliability of point-of-care hemoglobin testing devices such as HemoCue and iSTAT compared with the gold standard of complete blood count.¹⁴ The investigators recommended using complete blood count for accurate determination of the transfusion requirements during pediatric liver transplant surgery. Similarly, Kim and colleagues evaluated the accuracy of hematocrit measurement using a point-of-care analyzer during liver transplant and identified factors contributing to measurement errors.¹⁵ They found that point-of-care hematocrit values were falsely lower than laboratory values in a significant proportion of cases, highlighting the risk of incorrect measurements and unnecessary blood transfusion. Thus, although our study supports agreement between rapid blood-gas values and automatic laboratory values in pediatric renal transplant patients, it is important to consider the context of different patient populations and further investigate the accuracy and reliability of measurement methods in specific clinical scenarios.

Altunok and colleagues also conducted a study investigating the relationship between hemoglobin and electrolyte values measured by a blood-gas analyzer and automatic laboratory values in a large sample of children.⁴ However, they reported correlation coefficients for various parameters without finding satisfactory agreement limits for any of these parameters. Similarly, in a study conducted in our country among 1927 samples, results from blood-gas analyzers and automatic laboratory analyzers showed that the methods could not be used interchangeably.¹⁶ Although our study provided valuable insight on agreement between results from blood-gas values and automatic laboratory analyzers, larger studies are needed to further explore this topic.

Considering the divergent findings in the literature, our study contributes to the understanding of maintaining electrolyte balance and assessing hemoglobin levels in pediatric transplant patients. Our results support the compatibility between blood-gas measurements and automated laboratory tests in pediatric renal transplant patients. These findings have important implications for clinical practice and can offer valuable guidance to health care professionals in their decision-making processes. Overall, our research supports the use of blood-gas analysis as a viable option for assessment of sodium, potassium, and hemoglobin values in pediatric renal transplant recipients, offering a rapid and efficient means of monitoring electrolyte balance and hemostasis.

Although our study contributed important information to the existing literature, our study had some limitations. First, our study had a relatively small sample size. The inclusion of a limited number of patients may introduce potential biases and restrict the generalizability of our findings. Further investigations with larger sample sizes are warranted to enhance the robustness and reliability of the results. Second, expanding the scope of future studies to include multiple centers or conducting multi-institution collaborations would enhance the external validity and generalizability of the findings. Such collaborative efforts could also facilitate the exploration of other relevant parameters and potential confounding factors that were not accounted for in our research.

Conclusions

Rapid blood-gas analysis provided accurate and reliable measurements of hemoglobin, sodium, and potassium in pediatric kidney transplant recipients. Our results closely aligned with those obtained with an automated laboratory analyzer. Our results highlighted the significance of blood-gas analysis as a valuable and efficient method for assessing these parameters in clinical practice.

Table 1. Demographic and Transplant-Related Features of Study Patients

Figure 1. Bland-Altman Plots Comparing Measurements From Blood-Gas Test Versus Laboratory Automatic Analyzer

Table 2. Comparison of Differences Between Measurements of Sodium, Potassium, and Hemoglobin in 26 Patients Using Blood-Gas Test Versus Laboratory Automatic Analyzer

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