A community study of accuracy of blood glucose meter results

Journal of Diabetes Nursing, July-August, 2004 by Samantha Rosindale, Lynne Bower, Ellen Farleigh, Mike Francis, Christine Drew, Patricia Cooke

Introduction

The evidence that capillary blood glucose monitoring improves diabetes control is weak. Despite this, the net cost of testing materials was [pounds sterling]90 million in 2001 (Department of Health, 2002), and enthusiasm for their use continues to grow. One-hundred-and-two patients with type 1 and 2 diabetes were observed performing a capillary blood glucose test. Immediately afterwards, a venous sample was taken for glucose and the two values compared. Only 47% of patients' results were accurate to within 10% of their corresponding laboratory value (i.e. within the range deemed acceptable by the Medical Devices Agency). Healthcare professionals should review results from patients' glucose meters with caution.

This article summarises the current situation of self-monitoring, focused on the accuracy of the patients' blood glucose monitoring, and outlines some practical solutions for clinical practice.

KEY WORDS

* Capillary blood glucose monitoring

* Glucose meter

* Readings

* Accuracy

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Capillary blood glucose monitoring (CBGM) is established as an important tool in diabetes management for offering reassurance and warning of problems (Gallichan, 1993). Its importance has increased with the recognition that tight control of blood glucose levels are essential for risk reduction in developing micro- and macrovascular diabetic complications (Diabetes Control and Complications Trial, 1993; UKPDS, 1998). However, the evidence that CBGM improves diabetes control is weak (Worth et al, 1982; Burden, 1994; Gallichan, 1997; Miles et al, 1997). Despite this, the net cost of testing materials was [pounds sterling]90 million in 2001 (Department of Health, 2001) and enthusiasm for CBGM is growing (Diabetes UK, 2002).

Current technology has stimulated a rapid growth in the number of different glucose meters available. Subsequently, meters are sold commercially, given as gifts (e.g. friends and relatives), or can be obtained from a diabetes educator. The training available to patients, therefore, ranges from comprehensive to inadequate, or even none at all.

Glucose meter reliability

The Medical Devices Agency (MDA) has produced evaluation reports (2002) on all available meter types. Others have researched glucose meter reliability (Poirier et al, 1998; Day et al, 1999; Parkes et al, 2000), concluding that each of the available testing methods has satisfactory analytical performance for precision and accuracy under ideal conditions in the hands of experienced personnel.

However, true performance depends heavily upon the ability of non-specialist staff and patients to use the equipment satisfactorily in 'every day' situations. When capillary blood assays are performed in the laboratory the variables are carefully controlled and a high degree of accuracy is achieved.

Regular, accurate monitoring has been shown to promote empowerment for the patient (Fleming, 1994; Hounsome, 1998) with decision-making about treatment based on these results. However, American studies (Parkes et al, 2000; Ryan and Nguyen, 2001; Alto et al, 2002) have shown that 47-55% patients are not accurate to within 10% of the corresponding laboratory value despite national recommendations (American Diabetes Association, 1994).

Education

'Key' documents (Department of Health, 2002; National Institute for Clinical Excellence, 2002) are limited and lack detail for practical application as to which patients should be testing, guidance on training and how often tests should be performed.

Kabadi et al (1994) and Day et al (1999) evaluated training for both patients and nurses respectively, and discovered that incorrect results were the outcome of user error. They concluded that CBGM requires a robust system of training and review of performance, and that proficient use of glucose meters can be maintained with revision of CBGM skills at follow-up appointments.

Aim of the study

In the UK, background data are scarce for evaluation and formation of future benchmarks for CBGM. This needs to be addressed. Therefore, to establish how accurate patients' CBGM results are when compared to laboratory analysis would be a valid starting point.

Method

People with type 1 and type 2 diabetes who collected prescriptions for CBGM were randomly recruited from both primary and secondary care. The patients were observed performing CBGM 'how they usually do it'. It was noted whether adequate dosing of the meter strip and hand washing took place. The result from the meter was then recorded and immediately afterwards a venous blood sample for plasma glucose was taken. Some meters analyse plasma and some analyse whole blood so to allow for this because we analysed plasma in the laboratory before direct comparison, it had to be determined whether meters analysed plasma or whole blood. There was an allowance of +15% on meters that were calibrated to analyse whole blood.

The patients' own glucose meters were used. Venepuncture equipment was used and venous plasma assayed for glucose using glucose oxidase on a Roche 917 analyser. Ethical approval had been granted for this study.