This is an important capability in the management of diabetes mellitus. However, those with Type I diabetes usually have no secretion of insulin from the …
Greg Gardner
BME 422
Blood Glucose Meters
Glucose meters are a medical device capable of measuring a persons blood
glucose level, or blood sugar This is an important capability in the
management of diabetes mellitus They are usually used by those with Type
I diabetes, as opposed to Type II Many of those with Type II are able to
control their blood glucose levels with diet or prescription drugs and
frequent testing of blood sugar is unnecessary However, those with Type I
diabetes usually have no secretion of insulin from the pancreas This
means that they must inject insulin into themselves The amount of insulin
used is based on many factors, including individual resistance to the
synthetic insulin, number of carbohydrates ingested, etc
It is important for a diabetic to know their glucose levels It can become
high by ingesting carbohydrates and for other physiological reasons of
which the person may be unaware It may also go low because they
accidentally inject too much insulin or for more obscure physiological
reasons A blood glucose meter can tell them whether they need to inject
insulin or if they need to ingest carbohydrates This
knowledge is crucial
to diabetics Chronic hyperglycemia can cause many severe side affects
later, such as neuropathy, certain eye diseases, increased risk of heart
failure, etc Severe hypoglycemia can cause coma and death
While the ability to test the amount of glucose in a sample of blood in a
lab has been around for many years, it wasnt until around 1980 that a
system was developed for home use These meters were very bulky and
required large sample sizes Since that time, meters have shrunk to around
the size of a modern cellular phone and their accuracy has improved
Glucose meters have two important components The first is the meter
itself The second is disposable test strips A blood sample is deposited
onto the test strip after the strip has been placed in the meter
Depending on the exact meter, the blood glucose undergoes some sort of
chemical reaction while on the strip and some characteristic of this
reaction is measured by the meter This is converted to an electrical
signal that the meter uses to calculate the amount of glucose in the blood
generally in mg/dL
The earliest glucose meters had the blood undergo a color change based on
the amount of glucose in the
sample A beam of light was then bounced off
the sample A sensor then measured the amount of light that was reflected
From this measurement the blood glucose was calculated
Modern meters use electrochemical techniques to measure blood glucose
First, blood is deposited onto a test strip inserted in the glucose meter
A capillary sucks the blood down along with several chemicals present on
the test strip Two of these chemicals is glucose oxidase and potassium
ferricyanide The glucose oxidase molecules are actually part of an
electrode whose charge is readable by the glucose meter
Once the blood has been sucked down the test strip, the glucose in the
blood begins to react with the glucose oxidase Glucose oxidase is an
enzyme that performs the function it sounds like it should: oxidizing
glucose However, it cannot do this without another molecule to which it
can hand the extra electron That is why the potassium ferricyanide is
present Ferricyanide is very easily reduced So, to begin, glucose
attaches to a glucose oxidase enzyme The glucose is oxidized, forming
gluconolactone The ferricyanide accepts the electron, forming
ferrocyanide The electrode senses the charge
created by the movement of
electrons This reading is integrated into the glucose meters circuit
From this the meter is able to calculate the approximate glucose content of
the blood sample
There are two main processes by which to perform this calculation It can
either be done by letting the chemical reaction occur for a certain period
of time, or it can let the reaction run to equilibrium before calculating
the blood glucose level A meter that calculates glucose levels based on
the charge sensed by the electrodes over a fixed time period use the
coulometric method The majority of meters use this method A couple use
the amperometric method, allowing the reaction to run to completion, thus
measuring the total charge
Modern meters are almost all accurate to the same degree Each of them
tends to be within about 10-15 percent of the persons actual blood sugar
Several factors can affect the accuracy of a meter, whether affecting the
chemical reaction or the circuitry, including calibration of the meter,
temperature, humidity, size of blood sample, and age of the test strip
The 10-15 percent error can be a significant amount It is not a problem
for most Type I diabetics because
their blood glucose levels are normally
elevated Treatment for high blood sugar is essentially the same, although
the amount of insulin the person decides to take may be affected by the
error Accuracy can be even more crucial, however, for those who are
hypoglycemic due to disorders causing hyperinsulinism Normal blood
glucose is in the range of 70 - 100 mg/dl When a reading of 70 occurs
when ones blood glucose level is really 50 could be dangerous Many
people are able to physically feel when their blood sugar has dropped to a
dangerous level, but some are not very sensitive to the condition
Blood testing of the bodys glucose levels has improved greatly over the
past few decades, but a new glucose monitoring system has been developed
that may improve the diabetics lifestyle even further This system is
called the continuous glucose meter Two companies have these meters on
the market currently Both use a small probe that fits on the end of a
needle The needle is short is placed in the body so the probe is under
the skin The probe also contains a transmitter that sends a signal to a
receiver The receiver logs the persons blood sugar, which is updated
about every five
minutes An extra feature provided by the continuous
monitoring system is the ability to detect whether a persons blood sugar
is currently increasing or decreasing, a very important factor in deciding
how to treat the reading
There is currently research being done to basically add a feedback loop to
the continuous glucose monitoring device This would integrate an insulin
pump into the system The idea is similar to the feedback loop used by the
body to control blood glucose levels Usually, if blood glucose is
elevated the pancreas is signaled to increase insulin secretion When
blood glucose has fallen to a normal level, the pancreas is signaled to
decrease insulin secretion
This is exactly the same process that would be seen in this new system
The continuous glucose monitor would transmit a persons blood glucose
level to a receiver could be built into the insulin pump The insulin
pump reads the blood sugar level and decides whether to increase or
decrease insulin injection If an increase in insulin injection is
required, the pump can calculate the amount based on the blood glucose
reading and whether glucose levels are rising or
falling
Source:bme.unc.edu
