Electrolytes assessed by point-of-care testing - Are the values comparable with results obtained from the central laboratory?

Abstract

Background and Aims:When dealing with very sick patients, the speed and accuracy of tests to detect metabolic derangements is very important. We evaluated if there was agreement between whole blood electrolytes measured by a point-of-care device and serum electrolytes measured using indirect ion-selective electrodes.Materials and Methods:In this prospective study, electrolytes were analyzed in 44 paired samples drawn from critically ill patients. Whole blood electrolytes were analyzed using a point-of-care blood gas analyzer and serum electrolytes were analyzed in the central laboratory on samples transported through a rapid transit pneumatic system. Agreement was summarized by the mean difference with 95% limits of agreement (LOA) and Lin’s concordance correlation (p c).Results:There was a significant difference in the mean (±standard deviation) sodium value between whole blood and serum samples (135.8 ± 5.7 mmol/L vs. 139.9 ± 5.4 mmol/L, P < 0.001), with the agreement being modest (pc = 0.71; mean difference −4.0; 95% LOA −8.78 to 0.65). Although the agreement between whole blood and serum potassium was good (pc = 0.96), and the average difference small (−0.3; 95% LOA −0.72 to 0.13), individual differences were clinically significant, particularly at lower potassium values. For potassium values <3.0 mmol/L, the concordance was low (pc = 0.53) and the LOA was wide (1.0 to −0.13). The concordance for potassium was good (pc = 0.96) for values ≥3.0 (mean difference −0.2; 95% LOA −0.48 to 0.06).Conclusions:Clinicians should be aware of the difference between whole blood and serum electrolytes, particularly when urgent samples are tested at point of care and routine follow-up electrolytes are sent to the central laboratory. A correction factor needs to be determined at each center.

Concordance between point‐of‐care blood gas analysis and laboratory autoanalyzer in measurement of hemoglobin and electrolytes in critically ill patients

“…An understanding of differences, if any, in results of the same test performed on these machines and their clinical relevance, would be crucial to ascertain the implications in clinical decision‐making. The existing literature comparing these tests yielded mixed results and use of small sample sizes, study population, and method of sampling may have contributed to the discrepancy …”

“…The existing literature comparing these tests yielded mixed results and use of small sample sizes, study population, and method of sampling may have contributed to the discrepancy. [5][6][7][8][9] We tested the hypothesis that results of the same test performed on BGA machine and AA machine have high degree of concordance in an unselected population of critical care patients and that the two test methods could be used interchangeably. To test this hypothesis, we retrospectively analyzed the concordance between the electrolyte and hemoglobin values obtained from these two test methods using the largest sample size reported to date.…”

Electrolytes assessed by point-of-care testing

“…[2] We agree with the statement, “two samples that are processed in different times can have different laboratory data”. In our paper, we have stated that paired samples were collected at the same time from each patient.…”

Errors in potassium measurement: A laboratory perspective for the clinician

“…[40] found that while agreement between whole blood and serum was good, differences were large and clinically significant at concentrations below 3 mmol/L (whole blood measurements were up to 1 mmol/L lower compared to serum). The authors had used plastic lithium coated ABG syringes (DRIHEP A-LINE arterial blood gas collection syringe, 3.0 mL volume, 1.6 mL recommended draw Becton Dickinson Diagnostics ® , Plymouth, UK) for blood gas analysis to minimize the effect of heparin flushes and also determined that their pneumatic system did not significantly alter the electrolyte values.…”