Page 9 - Glucose Monitoring Devices

4 CHAPTER 1 Introduction to SMBG

blood removal step and the need for time reactions [9]. Toward the end of the 1980s,
test strips changed dramatically when electrochemical principles to measure blood
glucose were introduced. Furthermore, the introduction of electrochemical technol-
ogy led to the development of the third generation of glucose monitoring systems
[10]. The landmark in glucose self-monitoring was the release of the first electro-
chemical blood glucose monitor, ExacTech by Medisense, in 1987. The device
used an enzyme electrode strip containing glucose oxidase and ferrocene as an
electron transfer mediator. A current generated at the electrode was detected by
an amperometric sensor [11].
Today, most glucometers are electrochemical, using commercial screen-printed
strips based on the same principle. They require a smaller blood sample and provide
results in a few seconds. Glucose oxidase and glucose dehydrogenase are two types
of enzymes that have been used for commercial electrochemical blood glucose test
strips. Test strips using glucose oxidase technology are susceptible to dissolved
oxygen concentrations and can only be used with capillary blood in a normal range
of oxygen levels. Glucose dehydrogenase-based test strips are not sensitive to
oxygen [12]. However, coenzyme pyrroloquinoline quinone and glucose dehydroge-
nase containing test strips lack specificity as they cross-react with maltose,
galactose, and xylose. Therefore they must not be used by patients on peritoneal
dialysis [13]. The most common electrochemical detection methods for glucose
measurement are amperometry and coulometry [12]. Coulometric strips have
demonstrated to operate over the wider ranges of hematocrit values and with the
minimized effect of temperature, high concentrations of paracetamol, uric acid,
and vitamin C [14]. The performance of glucometers has further improved with
simplified sampling and testing procedures to minimize user interaction errors.
Meters using no-coding technology are precalibrated to report whole blood or
plasma equivalent results [15]. Most current meters are plasma calibrated and auto-
matically convert results into plasma equivalent results [16]. Modern electrochem-
ical blood glucose test strips use the capillary gap to automatically draw blood
into the test surface, which requires only a small volume of blood (just about
0.3 mL) and has automatic fill detection ensuring that sufficient volume of blood
is provided to the strip. The average test time has been reduced to just less than
5s [17]. In addition, lower blood volume requirements allow alternative sites for
blood glucose testing such as arm or thigh that are likely to be less painful and
provide similar results to the fingertip [18]. However, when blood glucose is chang-
ing rapidly, significant differences in blood glucose results can be anticipated due to
the time lag of up to 20 min at alternative sites [19]. Therefore testing at alternative
sites is not recommended within the early postmeal period, immediately after exer-
cise or when blood glucose is suspected to be low [20]. Some fully automated
devices have integral lacing device and extract blood by drawing a vacuum over a
lanced site [21]. Newer meters offer data-storage software that can be downloaded
and used by diabetes management systems for the graphical display of trends,
statistics, and sharing of reports [22]. Downloading information from blood glucose
meters enables the analysis of large amounts of data that reveal glycemic patterns