Browsing by Author "Johnson, Marianne"
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- ItemComparison of haemoglobin values measured at point of care with the standard laboratory value(Stellenbosch : Stellenbosch University, 2016-12) Johnson, Marianne; Marwick, Peter; Stellenbosch University. Faculty of Health Sciences. Dept. of Anaesthesiology and Critical Care.ENGLISH ABSTRACT: Point of care (POC) haemoglobin (Hb) concentration estimations guide acute decisions on red blood cell transfusion. We studied the accuracy of three POC devices when compared to central laboratory Hb testing and how between-method Hb disagreements could affect the decision to transfuse. The Health Research Ethics Committee of the University of Stellenbosch approved a method comparison study of perioperative Hb concentration measurement in arterial blood sampled from 58 adult cardiothoracic surgery patients. The Hb concentration was measured by using two Ilex GEM PremierTM 3500 blood gas analysers (Blood gas A and Blood gas B), a HemoCue® Hb 201+ System (HemoCue), and our central laboratory’s Siemens Advia® 2120 flow cytometry system (Laboratory haemoglobin). We regarded that a between-method Hb difference exceeding 10% (1 g/dL at an Hb value of 10 g/dL), would likely erroneously influence the transfusion decision. Furthermore, one unit of packed red blood cells will increase the Hb by ±1 g/dL and clinically represents the smallest transfusion associated risk that a patient will be exposed to. From the 58 patients included in the study, 70 central laboratory Hb concentration (Laboratory haemoglobin) measurements and 58, 72, and 71 measurements by the HemoCue, blood gas analyser A (Blood gas A) and blood gas analyser B (Blood gas B), respectively were taken. We found that the mean POC (HemoCue, Blood gas A, and Blood gas B) Hb levels underestimated the mean central laboratory Hb level by 0.79 g/dL, 0.81 g/dL, and 0.67 g/dL, respectively. The 95% confidence interval (CI) of the between-method difference revealed that unlike the Blood gas A (0.43 to 1.15 g/dL) and Blood gas B (0.46 to 1.16 g/dL) values, the HemoCue (0.47 to 0.87 g/dL) values did not breach the predetermined 1 g/dL limit. A Bland-Altman analysis revealed similar between-method mean Hb differences. However, the HemoCue upper and lower limits of agreement (LOA) were narrower, and the 95% CI of the LOAs do not overlap with those of Blood gas A and Blood gas B. Overall the HemoCue is more accurate. Also, the 95% CI of the HemoCue’s lower LOA was below 1 g/dL. This device does not give readings that clinically overestimate the Laboratory haemoglobin. Similarly, the mountain plot demonstrates the greater agreement and precision of the HemoCue device, as compared to Blood gas A and Blood gas B. An error grid analysis focused on the Hb 6 to 10 g/dL clinical decision-making range where only a 10% error was permitted. The error grid analysis revealed that the HemoCue and blood gas analysers had potential transfusion errors of less than 5% and more than 20%, respectively. However, none of the evaluated devices produced values in the major therapeutic error zone, where a decision to transfuse or not transfuse blood will be made erroneously.
- ItemComparison of hemoglobin measurements by 3 point-of-care devices with standard laboratory values and reliability regarding decisions for blood transfusion(Lippincott, Williams & Wilkins, 2020-08) Johnson, Marianne; Marwick, Peter C.; Coetzee, Johan F.BACKGROUND: We compared the accuracy of 3 point-of-care testing (POCT) devices with central laboratory measurements and the extent to which between-method disagreements could influence decisions to transfuse blood. METHODS: Hemoglobin concentrations [Hb] were measured in 58 adult patients undergoing cardiothoracic surgery using 2 Ilex GEM Premier 3500 blood gas analyzers (BG_A and BG_B) and a HemoCue Hb-201+ device (HemoCue). Measurements were compared with our central laboratory’s Siemens Advia 2120 flow cytometry system (laboratory [Hb] [Lab[Hb]]), regarded as the gold standard. We considered that between-method [Hb] differences exceeding 10% in the [Hb] range 6–10 g/dL would likely erroneously influence erythrocyte transfusion decisions. RESULTS: The 70 Lab[Hb] measurements ranged from 5.8 to 16.7 g/dL, of which 25 (36%) were <10.0 g/dL. Measurements by all 4 devices numbered 57. Mean POCT measurements did not differ significantly (P > .99). Results of the Bland–Altman analyses revealed statistically significant bias, with predominant underestimations by all 3 POCTs predominating. HemoCue upper and lower limits of agreement (LOA) were narrower, and the 95% confidence intervals (95% CIs) of the LOAs did not overlap with those of BG_A and BG_B. Similarly, a narrow mountain plot demonstrated greater precision for the HemoCue. Comparing BG_A with BG_B revealed no bias and narrow LOA. Error grid analysis within the [Hb] range 6–10 g/dL revealed that 5.3% of HemoCue measurements were beyond the permissible 10.0% error zone in contrast to 19.0% and 16.0% of the blood gas measurements. Possible inappropriate transfusion decisions based on POCT values generally erred toward unnecessary transfusions. Calculations of Cohen κ statistic indicated better chance-corrected agreement between HemoCue and Lab[Hb] regarding erythrocyte transfusions than the blood gas analyzers. CONCLUSIONS: All 3 POCT devices underestimated the Lab[Hb] and cannot be used interchangeably with standard laboratory measurements. BG_A and BG_B can be considered to be acceptably interchangeable with each other. Whereas the HemoCue had little bias and good precision, the blood gas analyzers revealed large bias and poor precision. We conclude that the tested HemoCue provides more reliable measurements, especially within the critical 6–10 g/dL range, with reduced potential for transfusion errors. Decisions regarding erythrocyte transfusions should also be considered in the light of clinical findings.