Department of Anaesthesiology and Critical Care
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Browsing Department of Anaesthesiology and Critical Care by browse.metadata.advisor "Marwick, Peter"
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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.