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Evaluating point-of-care glucose meters in the ICU

Karlijn Gijzen and Ayşe Y Demir
2 June, 2014  
Tight glycaemic control can be achieved through the use of point‑of-care glucose meters, but thorough evaluation of these devices is required before implementation in clinical practice
 
Karlijn Gijzen PhD
Ayşe Y Demir MD PhD
Department of Clinical Chemistry and Haematology,
Meander Medical Center, Amersfoort, The Netherlands
 
Tight glycaemic control in intensive care patients has become an increasingly common practice to decrease complications and mortality associated with abnormal glucose levels. Implementation of tight glycaemic control and avoidance of hypoglycaemia require frequent analysis of blood glucose. This can be achieved by accurate point-of-care (POC) hospital-use glucose meters. Nevertheless, the accuracy of POC glucose measurement in critically ill patients has been questioned.(1,2)
 
For example, interfering factors on blood glucose results, such as variable haematocrit values, state of perfusion, blood albumin concentration or medication, have been described.(3,4) Therefore, a correct evaluation of these devices is required before implementation in clinical practice. 
 
This article discusses the accuracy, limitations, and evaluation of current POC glucose meters in an intensive care setting. 
 
POC glucose meters
Originally, POC glucose meters were designed for home use and for self-monitoring for diabetes patients.5 The ease of use and rapid reporting of these devices has led to their use in hospitals. A number of POC glucose devices have been developed for hospital use including the Roche Accu-Check Inform II System, the HemoCue Glu201DM,the  Nova StatStrip, and the Abbott Precision Xceed Pro. 
 
Measurement of glucose
Measurement of glucose by POC is based on conversion of glucose by the enzymes glucose oxidase (GOX) or glucose-1-dehydrogenase (GDH).(3) The resulting reactants are detected using a photometric or amperometric technique.
 
For both techniques, interferences on the glucose measurement have been reported. For example, the GOX method is susceptible to extremes of oxygenation. High levels of dissolved oxygen in the sample (hyperoxia) can cause an underestimation of blood glucose, whereas low levels (hypoxaemia) can lead to an over-estimation. 
 
The GDH technique using coenzyme PQQ (pyrroloquinoline quinone) detects other sugars than glucose, that is, maltose and galactose. This can lead to falsely high glucose levels and, in some cases, can lead to critical treatment errors with significant consequences of hypoglycaemia.(5)
 
Furthermore, both the GOX and GDH methods are sensitive to interferences with specific drugs, including ascorbic acid and acetaminophen. High doses of ascorbic acid can result in falsely low glucose levels in the POC devices using one of these two measurement techniques. Therapeutic concentrations of acetaminophen can result in falsely low and falsely high glucose measurements with GOX and GDH devices, respectively.(5)
 
Additionally, several factors at extreme ranges (for example, haematocrit, bilirubin, pH and triglycerides) have been described as interfering with the blood glucose measurement.(3,4) For example, high haematocrit values may result in low glucose values due to influence on plasma diffusion into the reagent layer of the strip.3 At high concentrations, bilirubin can act as a reducing agent and interfere with the oxidation reaction.(6)
 
Changes in pH may affect the performance of POC meters. This is not a major source of error at the range 6.97–7.84, but have been described for extreme values such as <6.95 and >7.85.(3)
 
Finally, the sampling site (arterial, venous, capillary) can influence the glucose concentration. In the absence of stress and fasting,  differences in glucose concentration between these sites (arterial > capillary > venous) are insignificant. However, in critically ill patients, the presence of a hypermetabolic state and other stressors can cause significant differences between these values. Several studies in which capillary blood and arterial blood were compared for glucose analysis by POC showed that the glucose results from the capillary blood tests were inaccurate.(1,2,7) Therefore, arterial blood is preferred, and it is common practice to obtain blood from arterial lines instead of the finger-stick method in the ICU.(8) 
 
Besides these analytical- and patient-dependent factors, operator error can also be a major source of error on the glucose result.(3) Therefore, operator training is vital in ensuring testing quality. The operators of the POC devices at the wards are generally not analytically qualified. Therefore, the users should not only know the fundamentals of the POC meters and of performing the tests, but also know about policies for safety, specimen collection, quality control testing, critical values and the necessary documentation.6 Maintaining records of training and competency checks of personnel are required. 
 
To be able to fulfil all aforementioned requirements, a management system is required. Most of the POC meters for hospital use have a network interface, which means that the meters can be connected to the laboratory–hospital information system. This enables fast monitoring of the performance of the meters.(6) By means of currently available middleware systems, a complete management system for quality controls, patient demographics and results, and operator qualifications can be established. In this way the POC glucose measurement from the beginning to the end is traceable. For example, each glucose result is matched to time of testing, ward, operator ID, reagent lot number, comment codes, and quality control results. 
 
Accuracy
Accuracy of the POC glucose meters depends on many factors such the device measurement technology, sample source, patient attributes and technician skills. For reliable use of these devices, one should be aware of these factors in order to interpret the glucose results correctly. Clearly, accurate reporting of glucose results is essential to avoid potential life-threatening situations, especially in the intensive care setting. 
 
Evaluation in the intensive care setting
In critically ill patients, early signs of hypoglycaemia and hyperglycemia may be difficult to detect due to decreased mental status, sedatives, and other patient conditions. Inaccurate glucose values reported by POC tests could lead to serious patient safety risks and, therefore, accuracy of the POC devices is crucial in this patient group.(5)
 
Guidelines
In the literature, there is no consensus on how to evaluate accuracy of POC glucose meters in intensive care patients.(9) A number of guidelines have been described for evaluation of the accuracy of POC glucose meters,(10–15) such as International Organisation for Standardisation 15197 (ISO 15197), National Academy of Clinical Biochemistry/American Diabetes Association (NACB/ADA), Clinical Laboratory Standards Institute (CLSI), and Clarke Error grid guidelines. 
 
The ISO 15197:2003 was used by regulatory bodies as a minimum requirement for the performance of POC devices. This international guideline stated that 95% of the individual glucose measurements compared with the reference measurements are required to be in the range of ±15mg/dl (0.8mmol/l) for values ≤75mg/dl (4.2mmol/l) and ±20% for glucose values >75mg/dl (4.2mmol/l).(15) However, the ISO 15197 guideline was developed in 2003 and is now considered out of date and not stringent enough for current hospital demands. 
 
As a consequence, the ISO 15197 guideline was updated in 2013 and includes more stringent rules, including the requirement of a maximum of 15% deviation with glucose values >100mg/dl (5.6mmol/l).(16) This rule is similar to the NACB/ADA guideline.(11) 
 
Additionally, the ISO 15197:2013 guideline makes use of Park Error grid analysis. Park Error grid analysis,(13,14) defines several zones distinguishing whether the glucose result has a clinical impact or not. In this way, this type of analysis informs on the clinical significance of error and is a more clinically relevant standard.(10) Ideally, organisations responsible for establishing standards should also include a total error evaluation protocol.(10) In this type of protocol, glucose performance can be predicted in routine use and addresses all types of errors which includes analytical, pre- and post-analytical errors.
 
To ensure constant accuracy during routine use, an appropriate quality assurance programme is essential. Quality assurance programmes include a number of elements such as quality control testing, training programmes, reporting of results,  and equipment maintenance.(6) Quality assurance is performed by the laboratory because of its extensive experience and knowledge with regard to quality management procedures. The laboratory should be responsible for the complete process with regard to the POC meters, including purchase, personnel training, equipment maintenance, and trouble shooting. Ideally, a special POC group of technicians is assigned for these tasks. 
 
Conclusions
The choice of a POC device as a suitable glucose meter for an ICU is dependent on a number of factors. Although analytical performance will play a major role, pre-analytical and/or other confounding factors, such as user performance and choice of sampling site, will contribute to the decision. Unfortunately, the available guidelines do not make a distinction in the criteria that is applied on different type of glucose meters (home-use or hospital-use) or on different types of patient populations.
 
This results in a large variation in the findings that are reported in the literature and is not easily translatable to the own situation. There is a need for standardised guidelines that are more applicable to clinical decision making. Ideally, a glucose specification should also include a protocol that prevents exclusion of typical encountered conditions that could cause errors. This can be achieved by a total error evaluation protocol and the choice of the POC glucose meter is made after considering advantages and disadvantages of the respective methods. 
 
References 
  1. Critchell CD et al. Accuracy of bedside capillary blood glucose measurements in critically ill patients. Intensive Care Med 2007;33:2079–84.
  2. Kanji S et al. Reliability of point-of-care testing for glucose measurement in critically ill adults. Crit Care Med 2005;33:2778–85.
  3. Dungan K et al. Glucose measurement: confounding issues in setting targets for inpatient management. Diabetes Care 2007;30:403–9.
  4. Ginsberg BH. Factors affecting blood glucose monitoring: sources of errors in measurement. J Diabetes Sci Technol 2009;3:903–13.
  5. Rebel A, Rice MA, Fahy BG. The accuracy of point-of-care glucose measurements. J Diabet Sci Technol 2012;6(2):396–411.
  6. Hortin GL. Handbook of bedside glucose testing. AACC Press;1998.
  7. Petersen JR et al. Comparison of POCT and central laboratory blood glucose results using arterial, capillary, and venous samples from MICU patients on a tight glycemic protocol. Clin Chim Acta 2008;396:10–13.
  8. Lacara T et al. Comparison of point-of-care and laboratory glucose analysis in critically ill patients. Am J Crit Care 2007;16:336–46.
  9. Gijzen K et al. Is there a suitable point-of-care glucose meter for tight glycemic control? Evaluation of one home-use and four hospital-use meters in an intensive care unit. Clin Chem Lab Med 2012;50(11):1985–92.
  10. Krouwer JS, Cembrowski GS. A review of standards and statistics used to describe blood glucose monitor performance. J Diabetes Sci Technol 2010;4:75–83.
  11. Sacks DB et al. Guidelines and recommendations for laboratory analysis in the diagnosis and management of Diabetes Mellitus.  NACB/ADA Guidelines 2011. 
  12. CLSI/NCCLS. Point-of-care blood glucose testing in acute and chronic care facilities approved guideline. CLSI/NCCLS document C30-A2. Wayne, PA: NCCLS;2002.
  13. Clarke WL et al. Evaluating clinical accuracy of systems for self-monitoring of blood glucose. Diabetes Care.1987;10(5):622–8.
  14. Parkes JL et al. A new consensus error grid to evaluate the clinical significance of inaccuracies in the measurement of blood glucose. Diabetes Care 2000;23(8):1143–8.
  15. International Organization for Standardization. ISO 15197:2003. In vitro diagnostic test systems-requirements for blood-glucose monitoring systems for self-testing in managing diabetes mellitus.
  16. International Organization for Standardization. ISO 15197:2013. In vitro diagnostic test systems-requirements for blood-glucose monitoring systems for self-testing in managing diabetes mellitus.