Reliability of point of care assessments of hemoglobin, hematocrit and electrolytes obtained with blood gas device and central laboratory blood gas analyzer in critical emergency clinical setting 

Introduction: The Emergency Departments (ED) are equipped with Point-of-Care (POC) blood gas analysers (BGA) which deliver fast results on multiple parameters of arterial/venous blood. There is no consensus among ED physicians on the reliability of electrolyte results by POC Arterial Blood Gas (ABG) analysis compared to venous serum electrolyte from Central Laboratory Analyser/Auto-Analyser (CLA/AA). Aim: To compare the electrolyte(sodium and potassium) by POC arterial BGA (ABL800 Flex Radiometer) with venous electrolyte by CLA (Beckman Coulter AU 5800). Materials and Methods: This cross-sectional study was performed in the ED and Central Laboratory of the tertiary hospital from 1st July 2018 to 31st July 2019. A total of 254 critically ill adult patients with various etiologies, were enrolled in the study. The arterial and venous blood samples were collected for electrolyte measurement within a span of 15 minutes. The ABG samples, anticoagulated with liquid heparin, were processed in POC BGA. The venous samples collected in plain tubes were analysed in CLA. The results of sodium and potassium were compared by the mean, correlation coefficient, p-value, and Bland Altman Plots {95% Limit of agreement (LOA)}. Results: Out of 254 paired samples (mean age: 63±15 years), 157 (61.8%) were males and 97 (38.2%) females. The mean sodium values were 131.9±7.7 mmol/L in ABG and 132.3±7.1 mmol/L in CLA (p-value <0.0001). The mean difference was 0.4 mmol/L. The mean potassium values were 3.9±1.0 mmol/L (ABG) and 4.2±0.9 mmol/L (CLA), {p-value<0.0001}. The mean difference was 0.3 mmol/L. These differences were within the accepted range specified by the United States Clinical Laboratory Improvement Amendments. There were statistically significant strong positive correlations between the measurements of the two instruments r=0.78 for sodium and r=0.76 for potassium. The 95% LOA for sodium and potassium on both the instruments were -10.03 to 9.09 mmol/L and -1.49 to 0.97 mmol/L respectively, both wide and unacceptable. Conclusion: The arterial sodium and potassium measurements by BGA were not reliable in decision making in ED when compared to the venous serum by CLA as the 95% LOA was wide and unacceptable. Hence, sodium and potassium values by BGA alone might not be used as criteria for management without confirmation from venous serum values by CLA.

How reliable are electrolyte and metabolite results measured by a blood gas analyzer in the ED?

BackgroundElectrolyte values are measured both by arterial blood gas (ABG) analyzers and central laboratory auto-analyzers (AA), but a significant time gap exists between the availability of both these results, with the ABG giving faster results than the AA. The authors hypothesized that there is no difference between the results obtained after measurement of electrolytes by the blood gas and auto-analyzers.MethodsAfter approval by the ethics committee, an observational cohort study was conducted in which 200 paired venous and arterial samples from patients admitted to the Medical Intensive Care Unit (ICU) of Apollo Hospital, Hyderabad, India, were analyzed for electrolytes on the ABG machine and the AA. Analyses were done on the ABL555 blood gas analyzer and the Dade Dimension RxL Max, both located in the central laboratory. Statistical analyses were performed using paired Student’s t test.ResultsA total of 200 paired samples were analyzed. The mean ABG sodium value was 131.28 (SD 7.33), and the mean AA sodium value was 136.45 (SD 6.50) (p < 0.001). The mean ABG potassium value was 3.74 (SD 1.92), and the mean AA potassium value was 3.896 (SD 1.848) (p = 0.2679).ConclusionBased on the above analysis, the authors found no significant difference between the potassium values measured by the blood gas machine and the auto-analyzer. However, the difference between the measured sodium was found to be significant. We therefore conclude that critical decisions can be made by trusting the potassium values obtained from the arterial blood gas analysis.

Agreement of serum potassium measured by blood gas and biochemistry analyzer in patients with moderate to severe hyperkalemia

EDITOR: We assayed lactate levels in plasma using point-of-care analysers and obtained a fallaciously high value when compared to the value obtained from the central laboratory. The divergence in the lactate values suggested the possibility of ethylene glycol poisoning, but due to the limited information valuable time was lost in initiating treatment. A 36-yr-old male was brought to the hospital in an unconscious state with a core temperature of 32.9°C. Glasgow coma score on arrival in the accident and emergency department was 3. Clinical evaluation and an urgent computed tomography (CT) scan of the head ruled out intracranial pathology. The patient was moved to the critical care unit for further management. Blood gas analysis breathing 50% oxygen showed a pH of 6.8, PCO2 1.4 kPa, PO2 34 kPa, HCO3− 1.0 mmol L−1, base excess −26 mmol L−1 and lactate 33 mmol L−1. Routine blood tests showed a lactate of 15.8 mmol L−1. Past medical history revealed a suicidal tendency with previous admission to the hospital with paracetamol overdose. Toxicology screening was sent. A portable ultrasound of the abdomen was performed and contrast CT was planned to rule out intra-abdominal conditions. Fluid resuscitation, haemodynamic support, respiratory support and later renal replacement therapy were initiated. There was no improvement in acidosis despite treatment. All the arterial blood gas samples analysed from the critical care unit using a Radiometer ABL 725 (Radiometer Medical A/S, Bronshoj, Denmark) blood gas analyser showed consistently high levels of lactate despite a sodium bicarbonate infusion and haemofiltration. Thus the cause of the metabolic acidosis remained obscure. The lactate levels from the clinical chemistry laboratory taken at the same time did not match those from the ICU analyser. These differing results aroused the suspicion of ethylene glycol poisoning and further samples were sent for methanol/ethylene glycol detection to the regional toxicology laboratory. It was not before another 6 h that 333 mg L−1 of ethylene glycol was detected in the blood and appropriate treatment (4-Methylpyrazole) was instituted. Within an hour of this treatment the acidosis began to improve and the cardiovascular support could be reduced. The patient's condition progressively improved and the lactate had fallen to 0.5 mmol L−1 by the 4th day. He was discharged to a tertiary care unit for further management of his renal failure. We analysed some samples of plasma with a known quantity of glycolic acid and compared the results obtained from our ICU blood gas analyser with those from our central clinical chemistry laboratory (Cobas Integra 400 plus analyser; Roche Diagnostics, Basel, Switzerland). The levels of glycolic acid added and the discrepancies in the two sets of observations are shown in Table 1. This clearly demonstrates the lactate gap in all the readings, which increases linearly as the glycolic acid levels in plasma increased.Table 1: Glycolic acid measured as lactic acid.The delay in diagnosing this case of ethylene glycol poisoning could have been possibly averted by awareness of this artifactual elevation of lactate levels by our point-of-care analyser and facilities for the prompt detection of ethylene glycol in blood. The lactate gap has been described as divergent lactate levels obtained from a single sample when measured using two different modalities. Recently an erroneous reading by a Radiometer 700 analyser (Radiometer Limited, Crawley, UK) resulted in the patient having an emergency laparotomy [2]. Our patient presented to us approximately 12 h after ingestion of anti-freeze, an interval corresponding with high levels of toxic metabolites. Clearly, ethylene glycol metabolites were causing falsely elevated lactate levels. This was attributed to the large dose of ethylene glycol consumed and delay in the time of arrival at the hospital. The turning point in the diagnosis and subsequent management in our case were two different lactate values measured from the analyser in our critical care unit and that in the clinical chemistry laboratory. The method for lactate measurement in the latter equipment utilises a lactate oxidase method [3]. This enzyme converts lactate to pyruvate and produces hydrogen peroxide (H2O2). The peroxide reacts with 4-aminoantipyrine and other unspecified reactants to form a coloured product that is quantified colorimetrically. This method has the practical advantage of having improved reagent stability when compared to alternative methods based on lactate dehydrogenase. However, lactate oxidase may be less specific for the substrate lactate than lactate dehydrogenase. The l-lactate analyser such as that in our ICU, which is widely used to monitor lactate levels in critical care units, measures lactate using the l-lactate oxidase method. However, it uses an electrochemical principle. Lactate determination is accomplished by the enzymatic reaction of lactate oxidase and the detection of H2O2 [4]. It seems that most lactate oxidase-based systems respond to glycolate. The difference in response probably depends on the way in which the reaction is monitored. The false-positive results from the ICU equipment occur because ethylene glycol metabolites are substrates for l-lactate oxidase. In contrast, ethylene glycol metabolites cause minimal lactate elevation with the Bayer, iSTAT and Vitros devices [3]. Metabolites of ethylene glycol cause a worse acidosis than the parent compound itself. These may continue to remain in blood for a variable period of time. Increased glycols are measured as lactate in blood [1]. However, despite the equipment being used so frequently for blood gas analysis in the critical care unit, it has not been an object of attention for its erroneously high lactate readings in the presence of glycolic acid. Glycolic acid may account for as much as 96% of the anion gap in patients poisoned with ethylene glycol [5]. Point-of-care test systems may not mark the reaction course as atypical or erroneous. Therefore, having the local laboratory check a high lactate value is prudent, particularly if the diagnosis is not firmly established. In this regard it is useful to have previously established the response to glycolate of both point-of-care and laboratory systems. This case has highlighted the fact that more understanding of equipment and its mechanisms of action are critical in interpreting the data.

ObjectiveThe emergency departments (EDs) of Chinese hospitals are gradually being equipped with blood gas machines. These machines, along with the measurement of biochemical markers by the hospital laboratory, facilitate the care of patients with severe conditions who present to the ED. However, discrepancies have been noted between the Arterial Blood Gas (ABG) analyzers in the ED and the hospital laboratory autoanalyzer in relation to electrolyte and hemoglobin measurements. The present study was performed to determine whether the ABG and laboratory measurements of potassium, sodium, and hemoglobin levels are equivalent, and whether ABG analyzer results can be used to guide clinical care before the laboratory results become available.Materials and MethodsStudy power analyses revealed that 200 consecutive patients who presented to our ED would allow this prospective single-center cohort study to detect significant differences between ABG- and laboratory-measured potassium, sodium, and hemoglobin levels. Paired arterial and venous blood samples were collected within 30 minutes. Arterial blood samples were measured in the ED by an ABL 90 FLEX blood gas analyzer. The biochemistry and blood cell counts of the venous samples were measured in the hospital laboratory. The potassium, sodium, and hemoglobin concentrations obtained by both methods were compared by using paired Student’s t-test, Spearman’s correlation, Bland-Altman plots, and Deming regression.ResultsThe mean ABG and laboratory potassium values were 3.77±0.44 and 4.2±0.55, respectively (P<0.0001). The mean ABG and laboratory sodium values were 137.89±5.44 and 140.93±5.50, respectively (P<0.0001). The mean ABG and laboratory Hemoglobin values were 12.28±2.62 and 12.35±2.60, respectively (P = 0.24).ConclusionAlthough there are the statistical difference and acceptable biases between ABG- and laboratory-measured potassium and sodium, the biases do not exceed USCLIA-determined limits. In parallel, there are no statistical differences and biases beyond USCLIA-determined limits between ABG- and laboratory-measured hemoglobin. Therefore, all three variables measured by ABG were reliable.

Background:Near-patient testing allows rapid availability of results to enable prompt decision-making. Potassium abnormalities are common in acutely ill patients and can be associated with life-threatening complications. At times there is...

Are frequent calibrations enough? A patient-based quality control perspective on blood gas and laboratory analyzers.

Background: In hemodialysis patients, precise hemoglobin (Hb) monitoring is essential for anemia management. Point-of-care blood gas analyzers (BGAs), such as the ABL800 Flex, offer rapid Hb determinations, but their accordance and comparability with central laboratory measurements remains to be assessed in the hemodialysis setting. Methods: We performed a retrospective analysis (April 2017-February 2024) of 10,802 paired Hb measurements from 291 hemodialysis patients. BGA and laboratory values within 90 min were compared using paired t-tests, non-inferiority testing (margin 0.5 g/dL), a Bland-Altman analysis, and linear regression. Results: The mean ± standard deviation Hb (g/dL) values were 10.14 ± 1.64 (BGA) versus 9.90 ± 1.55 (laboratory). The overall mean difference (BGA-laboratory) was 0.24 ± 0.49 g/dL (95% CI: 0.23-0.25), demonstrating non-inferiority (p < 0.0001). Measurement delay correlated with increasing analysis discrepancies (mean difference in g/dL: 0.22 at <30 min vs. 0.27 at 60-90 min; p < 0.001). We derived the equation of laboratory Hb = 0.90 × BGA Hb + 0.72; a simplified correction (BGA-0.3 g/dL) produced a mean absolute error (MAE) of 0.30 g/dL and root mean square error (RMSE) of 0.50 g/dL, and patient-level 10-fold cross-validation yielded MAE ≈ 0.30 and RMSE ≈ 0.49 g/dL. The Bland-Altman analysis confirmed a small systematic bias of 0.24 g/dL with 95% limits of agreement ranging from -0.73 to +1.21 g/dL. Conclusions: BGA Hb measurements via the ABL800 Flex are non-inferior to central laboratory values across clinical scenarios, with minimal bias. After regression correction, the estimated total error was ≈0.78 g/dL. If hemodialysis centers accept this level of total error and apply confirmatory testing near decision points, BGA could be used to guide anemia management.

Background. Blood gas analyzers (BGAs) are important in assessing and monitoring critically ill patients. However, the random use of BGAs to measure blood gases, electrolytes and metabolites increases the variability in test results. Therefore, this study aimed to investigate the correlation of blood gas, electrolyte and metabolite results measured with two BGAs and a core laboratory analyzer. Methods. A total of 40 arterial blood gas samples were analyzed with two BGAs [(Nova Stat Profile Critical Care Xpress (Nova Biomedical, Waltham, MA, USA) and Siemens Rapidlab 1265 (Siemens Healthcare Diagnostics Inc., Tarrytown, NY, USA)) and a core laboratory analyzer [Olympus AU 2700 autoanalyzer (Beckman-Coulter, Inc., Fullerton, CA, USA)]. The results of pH, pCO2, pO2, SO2, sodium (Na+), potassium (K+), calcium (Ca+ 2), chloride (Cl−), glucose, and lactate were compared by Passing-Bablok regression analysis and Bland-Altman plots. Results. The present study showed that there was negligible variability of blood gases (pCO2, pO2, SO2), K+ and lactate values between the blood gas and core laboratory analyzers. However, the differences in pH were modest, while Na+, Cl−, Ca2+ and glucose showed poor correlation according to the concordance correlation coefficient. Conclusions. BGAs and core laboratory autoanalyzer demonstrated variable performances and not all tests met minimum performance goals. It is important that clinicians and laboratories are aware of the limitations of their assays.

Background:A blood gas analyzer is a point-of-care (POC) testing device used in the Emergency Department (ED) to manage critically ill patients. However, there were differences in results found from blood gas analyzers for hemoglobin (Hgb) and electrolytes parameters. We conducted a comparative validity study in ED in patients who had requirements of venous gas analysis, complete blood count, and electrolytes. The objective was to find the correlation of Hgb, sodium (Na+), and potassium (K+) values between the blood gas analyzer and laboratory autoanalyzer.Methods:A total of 206 paired samples were tested for Hgb, Na+, and K+. Total 4.6 ml of venous blood was collected from each participant, 0.6 ml was used for blood gas analysis as POC testing and 4 ml was sent to the central laboratory for electrolyte and Hgb estimation.Results:The mean difference between POC and laboratory method was 0.608 ± 1.41 (95% confidence interval [CI], 0.41–0.80; P < 0.001) for Hgb, 0.92 ± 3.5 (95% CI, 0.44–1.40) for Na+, and 0.238 ± 0.62 (95% CI, −0.32–0.15; P < 0.001) for K+. POC testing and laboratory method showed a strong positive correlation with Pearson correlation coefficient (r) of 0.873, 0.928, and 0.793 for Hgb, Na+, and K+, respectively (P < 0.001).Conclusion:Although there was a statistical difference found between the two methods, it was under the United States Clinical Laboratory Improvement Amendment range. Hence, starting the therapy according to the blood gas analyzer results may be beneficial to the patient and improve the outcome.

Telephone Reporting of Blood Analysis Results into the Operating Room

Clinicians calculate the anion gap (AG) and the strong ion difference (SID) to make acid-base diagnoses. The technology used is assumed to have limited impact. The authors hypothesized that different measurement technologies markedly affect AG and SID values. SID and AG were calculated using values from the point-of-care blood gas and electrolyte analyzer and the central hospital laboratory automated blood biochemistry analyzer. Simultaneously measured plasma sodium, potassium, and chloride concentrations were also compared. Mean values for central laboratory and point-of-care plasma sodium concentration were significantly different (140.4 +/- 5.6 vs. 138.3 +/- 5.9 mm; P < 0.0001), as were those for plasma chloride concentration (102.4 +/- 6.5 vs. 103.4 +/- 6.0 mm; P < 0.0001) but not potassium. Mean AG values calculated with the two different measurement techniques differed significantly (17.6 +/- 6.2 mEq/l for central laboratory vs. 14.5 +/- 6.0 mEq/l for point-of-care blood gas analyzer; P < 0.0001). Using the Stewart-Figge methodology, SID values also differed significantly (43.7 +/- 4.8 vs. 40.7 +/- 5.6 mEq/l; P < 0.0001), with mean difference of 3.1 mEq/l (95% limits of agreement, -3.4, 9.5 mEq/l). For 83 patients (27.6%), differences in AG values were as high as 5 mEq/l or more, and for 46% of patients whose AG value was outside the reference range with one technology, a value within normal limits was recorded with the other. Results with two different measurement technologies differed significantly for plasma sodium and chloride concentrations. These differences significantly affected the calculated AG and SID values and might lead clinicians to different assessments of acid-base and electrolyte status.

Four hundred and twenty four premature infants had been admitted in the premature infant nursery of Pediatric Department, Kansai Medical University for five years from 1968 to 1972. They were studied statistically, especially on mortality and morbidity of respiratory disorders at first and then relationship between arterial blood gas analysis and clinical symptoms was studied mainly on these infants with respiratory disorders and the following results were obtained.1) Seventy eight cases of 424 admitted infants died of various conditions and the mortality rate in this nursery (all infants were transported out of the hospital) was 18.3 %. Fourty two cases died of idiopathic respiratory distress syndrome, which showed the highest mortality of 9.9%.2) Arterial blood gas analyses were done on two samples, arterialized blood obtained by heel puncture and radial artery blood. It was confirmed that the arterialized blood from heel puncture could not be used for monitoring PaO2.3) Comparing Silverman's retraction score and blood gas analysing results between infants transported in incubator and infants without incubator, the former showed the better data in blood gas analysis. It was emphasized that infants with respiratory distress should be transported in incubator.4) Silverman's retraction score in IRDS correlates well to results of blood gas analysis, and may be an effective index to show the course of IRDS, if blood gas analysis is not available.5) Evaluation of high risk infants by means of results of blood gas analysis immediately after admission is very important for an assessment of prognosis and decision of therapeutic regimens. The blood gas analyser, therefore, should be used in the nursery, to check the blood at whenever time necessary.6) It was reconfirmed that the blood gas analysis is indispensable as a fundamental test to assess the effects of treatments, including oxygen therapy and alkali therapy for high risk infants, especially for IRDS.

Point-of-care testing allows rapid analysis and short turnaround times. To the best of our knowledge, the present study assesses, for the first time, clinical, operative, and economic outcomes of point-of-care blood gas analysis in a nephrology department. To evaluate the impact after implementing blood gas analysis in the nephrology department, considering clinical (differences in blood gas analysis results, critical results), operative (turnaround time, elapsed time between consecutive blood gas analysis, preanalytical errors), and economic (total cost per process) outcomes. A total amount of 3195 venous blood gas analyses from 688 patients of the nephrology department before and after point-of-care blood gas analyzer installation were included. Blood gas analysis results obtained by ABL90 FLEX PLUS were acquired from the laboratory information system. Statistical analyses were performed using SAS 9.3 software. During the point-of-care testing period, there was an increase in blood glucose levels and a decrease in pCO2, lactate, and sodium as well as fewer critical values (especially glucose and lactate). The turnaround time and the mean elapsed time were shorter. By the beginning of this period, the number of preanalytical errors increased; however, no statistically significant differences were found during year-long monitoring. Although there was an increase in the total number of blood gas analysis requests, the total cost per process decreased. The implementation of a point-of-care blood gas analysis in a nephrology department has a positive impact on clinical, operative, and economic terms of patient care.