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Glucose Meters
(Blood Glucose Meters)
When people with diabetes can control their
blood sugar (glucose), they are more likely to stay healthy. People with
diabetes use two kinds of management devices: glucose meters and other diabetes
management tests. Glucose meters help people with diabetes check their blood
sugar at home, school, work, and play. Other blood and urine tests reveal trends
in diabetes management and help identify diabetes complications
Glucose Meters
Self-Monitoring of Blood Glucose
The process of monitoring one's own blood
glucose with a glucose meter is often referred to as self-monitoring of blood
glucose or "SMBG."
To test for glucose with a typical glucose
meter, place a small sample of blood on a disposable "test strip" and place the
strip in the meter. The test strips are coated with chemicals (glucose oxidase,
dehydrogenase, or hexokinase) that combine with glucose in blood. The meter
measures how much glucose is present. Meters do this in different ways. Some
measure the amount of electricity that can pass through the sample. Others
measure how much light reflects from it. The meter displays the glucose level as
a number. Several new models can record and store a number of test results. Some
models can connect to personal computers to store test results or print them
out.
Choosing a Glucose Meter
At least 25 different meters are commercially
available.
They differ in several ways including
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Amount of blood needed for each test
-
Testing speed
-
Overall size
-
Ability to store test results in memory
-
Cost of the meter
-
Cost of the test strips used
Newer meters often have features that make them
easier to use than older models. Some meters allow you to get blood from places
other than your fingertip (Alternative Site Testing). Some new
models have automatic timing, error codes and signals, or barcode readers to
help with calibration. Some meters have a large display screen or spoken
instructions for people with visual impairments.
Using Your Glucose Meter
Diabetes care should be designed for each
individual patient. Some patients may need to test (monitor) more often than
others do. How often you use your glucose meter should be based on the
recommendation of your health care provider. Self-monitoring of blood glucose (SMBG)
is recommended for all people with diabetes, but especially for those who take
insulin. The role of SMBG has not been defined for people with stable type 2
diabetes treated only with diet.
As a general rule, the American Diabetes
Association (ADA) recommends that most patients with type 1 diabetes test
glucose three or more times per day. Pregnant women taking insulin for
gestational diabetes should test two times per day. ADA does not specify how
often people with type 2 diabetes should test their glucose, but testing often
helps control.
Often, self-monitoring plans direct you to test
your blood sugar before meals, 2 hours after meals, at bedtime, at 3 a.m., and
anytime you experience signs or symptoms. You should test more often when you
change medications, when you have unusual stress or illness, or in other unusual
circumstances.
Learning to Use Your Glucose Meter
Not all glucose meters work the same way. Since
you need to know how to use your glucose meter and interpret its results, you
should get training from a diabetes educator. The educator should watch you test
your glucose to make sure you can use your meter correctly. This training is
better if it is part of an overall diabetes education program.
Instructions for Using Glucose Meters
The following are the general instructions for
using a glucose meter:
1. Wash hands with soap and warm water and dry
completely or clean the area with alcohol and dry completely.
2. Prick the fingertip with a lancet.
3. Hold the hand down and hold the finger until a small drop of blood appears;
catch the blood with the test strip.
4. Follow the instructions for inserting the test strip and using the SMBG
meter.
5. Record the test result.
FDA requires that glucose meters and the strips
used with them have instructions for use. You should read carefully the
instructions for both the meter and its test strips. Meter instructions are
found in the user manual. Keep this manual to help you solve any problems that
may arise. Many meters use "error codes" when there is a problem with the meter,
the test strip, or the blood sample on the strip. You will need the manual to
interpret these error codes and fix the problem.
You can get information about your meter and
test strips from several different sources. Your user manual should include a
toll free number in case you have questions or problems. If you have a problem
and can't get a response from this number, contact your healthcare provider or a
local emergency room for advice. Also, the manufacturer of your meter should
have a website. Check this website regularly to see if it lists any issues with
the function of your meter.
New devices are for sale such as laser lancets
and meters that can test blood taken from "alternative sites" of the body other
than fingertips. Since new devices are used in new ways and often have new use
restrictions, you must review the instructions carefully.
Important Features Of Glucose Meters
There are several features of glucose meters
that you need to understand so you can use your meter and understand its
results. These features are often different for different meters. You should
understand the features of your own meter.
Measurement Range. Most glucose meters
are able to read glucose levels over a broad range of values from as low as 0
to as high as 600 mg/dL. Since the range is different among meters, interpret
very high or low values carefully. Glucose readings are not linear over their
entire range. If you get an extremely high or low reading from your meter, you
should first confirm it with another reading. You should also consider
checking your meter's calibration.
Whole Blood Glucose vs. Plasma Glucose. Glucose levels in plasma
(one of the components of blood) are generally 10-15% higher than glucose
measurements in whole blood (and even more after eating). This is important
because home blood glucose meters measure the glucose in whole blood
while most lab tests measure the glucose in plasma. There are many
meters on the market now that give results as "plasma equivalent". This allows
patients to easily compare their glucose measurements in a lab test and at
home. Remember, this is just the way that the measurement is presented to you.
All portable blood glucose meters measure the amount of glucose in whole
blood. The meters that give "plasma equivalent" readings have a built in
algorithm that translates the whole blood measurement to make it seem like the
result that would be obtained on a plasma sample. It is important for you and
your healthcare provider to know whether your meter gives its results as
"whole blood equivalent" or "plasma equivalent."
Cleaning. Some meters need regular cleaning to be accurate. Clean
your meter with soap and water, using only a dampened soft cloth to avoid
damage to sensitive parts. Do not use alcohol (unless recommended in the
instructions), cleansers with ammonia, glass cleaners, or abrasive cleaners.
Some meters do not require regular cleaning but contain electronic alerts
indicating when you should clean them. Other meters can be cleaned only by the
manufacturer.
Display Of High And Low Glucose Values. Part of learning how to
operate a meter is understanding what the meter results mean. Be sure you know
how high and low glucose concentrations are displayed on your meter.
Factors That Affect Glucose Meter Performance
The accuracy of your test results depends partly
on the quality of your meter and test strips and your training. Other factors
can also make a difference in the accuracy of your results.
Hematocrit. Hematocrit is the amount of
red blood cells in the blood. Patients with higher hematocrit values will
usually test lower for blood glucose than patients with normal hematocrit.
Patients with lower hematocrit values will test higher. If you know that you
have abnormal hematocrit values you should discuss its possible effect on
glucose testing (and HbA1C testing) with your health care provider. Anemia and
Sickle Cell Anemia are two conditions that affect hematocrit values.
Other Substances. Many other substances may interfere with your
testing process. These include uric acid (a natural substance in the body that
can be more concentrated in some people with diabetes), glutathione (an
"anti-oxidant" also called "GSH"), and ascorbic acid (vitamin C). You should
check the package insert for each meter to find what substances might affect
its testing accuracy, and discuss your concerns with your health care
provider.
Altitude, Temperature and Humidity. Altitude, room temperature, and
humidity can cause unpredictable effects on glucose results. Check the meter
and test strip package insert for information on these issues. Store and
handle the meter and test strips according to the instructions.
Third-Party Test Strips. Third-party or "generic glucose reagent
strips" are test strips developed as a less expensive option than the strips
that the manufacturer intended the meter to be used with. They are typically
developed by copying the original strips. Although these strips may work on
the meter listed on the package, they could look like strips used for other
meters. Be sure the test strip you use is compatible with your glucose meter.
Sometimes manufacturers change their meters and their test strips. These
changes are not always communicated to the third-party strip manufacturers.
This can make third-party strips incompatible with your meter without your
knowledge. Differences can involve the amount, type or concentration of the
chemicals (called "reagents") on the test strip, or the actual size and shape
of the strip itself. Meters are sensitive to these features of test strips and
may not work well or consistently if they are not correct for a meter. If you
are unsure whether or not a certain test strip will work with you meter,
contact the manufacturer of your glucose meter.
Making Sure Your Meter Works Properly
You should perform quality-control checks to make sure that your home glucose
testing is accurate and reliable. Several things can reduce the accuracy of your
meter reading even if it appears to still work. For instance, the meter may have
been dropped or its electrical components may have worn out. Humidity or heat
may damage test strips. It is even possible that your testing technique may have
changed slightly. Quality control checks should be done on a regular basis
according to the meter manufacturer's instructions. There are two kinds of
quality control checks:
Check Using "Test Quality Control
Solutions" or "Electronic Controls". Test quality control solutions and
electronic controls are both used to check the operation of your meter. Test
quality control solutions check the accuracy of the meter and test strip. They
may also give an indication of how well you use your system. Electronic
controls only check that the meter is working properly.
Test quality control solutions have known glucose values. Essentially, when
you run a quality control test, you substitute the test solution for blood.
The difference is that you know what the result should be.
To test your meter with a quality control solution, follow the instructions
that accompany the solution. These will guide you to place a certain amount of
solution on your test strip and run it through your meter. The meter will give
you a reading for the amount of glucose in the sample. Compare this number to
the number listed on the test quality control solution. If the results of your
test match the values given in the quality control solution labeling, you can
be assured the entire system (meter and test strip) is working properly. If
results are not correct, the system may not be accurate--contact the
manufacturer for advice.
Manufacturers sometimes include quality control solution with their meter.
However, most often you must order it separately from a manufacturer or
pharmacy.
Some glucose meters also use electronic controls to make sure the meter is
working properly. With this method, you place a cartridge or a special
"control" test strip in the meter and a signal will appear to indicate if the
meter is working.
Take Your Meter with You to The Health Care Provider's Office. This
way you can test your glucose while your health care provider watches your
technique to make sure you are using the meter correctly. Your healthcare
provider will also take a sample of blood and evaluate it using a routine
laboratory method. If values obtained on the glucose meter match the
laboratory method, you and your healthcare provider will see that your meter
is working well and that you are using good technique. If results do not match
the laboratory method results, then results you get from your meter may be
inaccurate and you should discuss the issue with your healthcare provider and
contact the manufacturer if necessary.
User Experiences with Glucose Meters
The FDA's Center for Devices and Radiological
Health (CDRH) held a series of focus groups on blood glucose meter use in 2001.
The twenty-two members participated in six groups. They were all government
employees, mostly from CDRH. They were either people with diabetes or family
members of people with diabetes who were familiar with the use of glucose
meters.
Most of the participants in these groups were
satisfied with their meters. Some were quite enthusiastic about the new models.
A few had some concerns about meters. One such participant stated: "The first
meter I got I couldn't use because it was too difficult."
Repeating Tests. Most users repeated
tests now and then because they believed the first test result was incorrect.
Users questioned test results based on their expectations about what the
results should be. If the glucose level seemed "off," they repeated the test.
The ability to judge whether or not a test seemed accurate appeared to come
from the users' experiences with their meters. These experiences helped them
know how they felt when their glucose level was high, when it was low and when
it was about right. They also were aware of what and when they had eaten,
exercised, slept, or taken insulin, and they learned to anticipate the effect
these activities have on their glucose levels.
Comments users made about their results include the following:
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I sometimes get a reading of perhaps 300 and then
180 on a retest. This happens in about 1 in 50 tests.
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Glucose tablet residue on my finger can throw
results way off.
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I get some inaccurate readings - especially when
the meter is new.
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Sometimes I get higher readings than I expect,
probably because the meter was left out of the case or food got on it.
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The date wears off of the vial and I end up using
expired strips.
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Humidity around the bathroom seems to affect
performance of the strips.
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If I have wet hands, my results tend to be higher
than expected.
Besides repeating tests because of a suspected inaccuracy in the first
test, a frequent reason to repeat a test was that the meter indicated
"insufficient blood" on the test strip and would not complete the test on the
first attempt. When this happens, users needed to do another fingerstick.
Users whose meters required less blood did not have this problem as often.
Feelings about Fingersticks. Surprisingly, most of the participants
stated that fingerstick discomfort was not a big concern - even with children:
"At first, fingersticks were a real problem, but now it doesn't bother her."
Most participants stated that discomfort was an issue when they first
started to use the meter; this was especially true for children, but that the
discomfort grew less important after a few weeks or months of use.
However, one participant of a "fragile" child with diabetes stated: "We
test 8 to 10 times a day. He was losing sensitivity in his fingertips [from
the frequent fingersticks]. We prefer the meter that allows testing in
alternative sites."
Use of Test Solution. Most users did not use test solution often.
Some never used it. They stated that the solution was difficult to use because
it expired in a month, it was difficult to order, and they were not convinced
that it helped.
Important Features. Users discussed and rated aspects of meters such
as accuracy, ease-of-use, cost of the meter, cost of test strips, size,
whether it was recommended by a friend etc. The most important consideration
in this group was accuracy. This was followed by "ease of use" and then
affordability.
New Technologies: Alternative Site Testing
Some glucose meters allow testing blood from
alternative sites, such as the upper arm, forearm, base of the thumb, and thigh
Sampling blood from alternative sites may be
desirable, but it may have some limitations. Blood in the fingertips show
changes in glucose levels more quickly than blood in other parts of the body.
This means that alternative site test results may be different from fingertip
test results not because of the meter's ability to test accurately, but because
the actual glucose concentration can be different. FDA believes that further
research is needed to better understand these differences in test values and
their possible impact on the health of people with diabetes.
Glucose concentrations change rapidly after a
meal, insulin or exercise. Glucose levels at the alternative site appear to
change more slowly than in the fingertips. Because of this concern, FDA has now
requested that manufacturers either show their device is not affected by
differences between alternative site and fingertip blood samples during times of
rapidly changing glucose, or alert users about possible different values at
these times.
Recommended labeling precautions include these
statements:
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Alternative site results may be different than
the fingertip when glucose levels are changing rapidly (e.g. after a meal,
taking insulin or during or after exercise).
-
Do not test at an alternative site, but use
samples taken from the fingertip, if
-
you think your blood sugar is low,
-
you are not aware of symptoms when you become
hypoglycemic, or
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the site results do not agree with the way you
feel.
In October, 2001, FDA held a public meeting to
discuss the types of information and labeling needed for glucose measuring
devices if the blood sample is taken from alternative sites rather than the
fingertip. Presenters included manufacturers of blood glucose meters, healthcare
providers, people with diabetes, and parents of children with diabetes.
Minimally Invasive and Non-Invasive Glucose
Meters
Researchers are exploring new technologies for
glucose testing that avoid fingersticks. One of these is based on near-infrared
spectroscopy for measurement of glucose. Essentially, this amounts to measuring
glucose by shining a beam of light on the skin. It is painless. There are
increasing numbers of reports in the scientific literature on the challenges,
strengths, and weaknesses of this and other new approaches to testing glucose
without fingersticks.
FDA has approved one "minimally invasive" meter
and one "non-invasive" glucose meter. Neither of these should replace standard
glucose testing. They are used to obtain additional glucose values between
fingerstick tests. Both devices require daily calibration using standard
fingerstick glucose measurements and both remain the subject of continuing
studies to find how they are best used as tools for diabetes management.
MiniMed Continuous Glucose Monitoring
System. The MiniMed system consists of a small plastic catheter (very
small tube) inserted just under the skin. The catheter collects small amounts
of liquid that is passed through a "biosensor" to measure the amount of
glucose present.
Minimed is intended for occasional use and to discover trends in glucose
levels during the day. It does not give you readings for individual tests and
therefore you can't use it for typical day-to-day monitoring. The device
collects measurements over a 72-hour period and then must be downloaded by the
patient or healthcare provider. Understanding trends over time might help
patients know the best time to do their standard fingerstick tests. You need a
prescription to buy MiniMed.
Cygnus GlucoWatch Biographer. GlucoWatch is worn on the arm like a
wristwatch. It pulls tiny amounts of fluid from the skin and measures the
glucose in the fluid without puncturing the skin. The device requires 3 hours
to warm up after it is put on. After this, it can provide up to 3 glucose
measurements per hour for 12 hours. Unlike the MiniMed device, the GlucoWatch
displays results that can be read by the wearer, although like the MiniMed
device, these readings are not meant to be used as replacements for
fingerstick-based tests. The results are meant to show trends and patterns in
glucose levels rather than report any one result alone. It is useful for
detecting and evaluating episodes of hyperglycemia and hypoglycemia. However,
you must confirm its results with a standard glucose meter before you take
corrective action. You need a prescription to buy GlucoWatch.
How FDA Regulates Glucose Meters
FDA reviews all glucose meters and test strips
before they can be marketed to the public. This FDA "premarket" review process
requires the manufacturer of the meter to show that the meter system provides
acceptable accuracy and consistency of glucose measurement at high, medium and
low levels of glucose as compared to glucose meters already being sold. The
quality of software is an increasingly important feature of glucose meters since
it controls the testing and data storage and controls the displays that the user
sees and uses when testing.
FDA also considers possible interference from
over-the-counter medications, prescription medications, and vitamin supplements.
FDA also asks for data showing how well the
meter has performed during actual use (a type of human factors study). These
studies ensure that users understand the labeling, achieve good results, and
avoid experiencing problems that could affect their health.
FDA quality system regulations require that
manufacturers who make glucose meters follow the same quality standards every
time. In this way, users can be assured that new meters and strips perform as
well as older models.
FDA's responsibility for medical devices does
not end when the devices enters the market. To monitor the quality of products,
FDA routinely inspects manufacturing facilities. It also receives information
from the manufacturers, health providers and the general public through the
MedWatch system.
Reporting Problems with Glucose Meters to FDA
FDA learns about problems with medical products
through the MedWatch program. Consumers can report problems with medical
devices, including glucose meters, through MedWatch.
Performance Goals for Glucose Meters
Deciding performance standards for glucose
meters has been controversial and challenging. In spite of effort in the late
1970s and 1980s by both FDA and CDC, no universally accepted standards or
testing methods have been developed for the measurement of glucose. CDC (Centers
for Disease Control and Prevention) recently held a standards conference and is
exploring the possibility of developing a standard reference material for whole
blood.
The ADA has recommended accuracy goals twice
over the past twenty years, once in 1986 (target accuracy of +/- 15%) and once
in 1993 (target accuracy of +/- 5%) No company that manufacturers glucose meters
has developed a cost-effective system to meet these goals. A number of
alternative standards have been suggested by national standards organizations in
the U.S., Canada, and Europe. An international standard ISO DIS 15197 is
currently under development that recommends accuracy of +/- 20 mg/dl for glucose
values under 100 mg/dl and +/- 20% for higher glucose values.
Although data on glucose meters continue to show
variable performance, the newest generations of meters are simpler to use and
more accurate than older models. Improvements in the chemical, mechanical and
software components of glucose meters are continuing to help with the management
of diabetes.
A Brief History of Self-Monitoring of Blood
Glucose with Glucose Meters
Anton Hubert Clemens received the first patent
for a blood glucose meter called the Ames Reflectance Meter on September 14,
1971. Richard K. Bernstein, an insulin dependent physician with diabetes, was
one of the first patients to monitor his blood glucose at home using a glucose
meter. He published a report on his experiences in an early volume of the
medical journal, Diabetes Care. He has also written a book on this subject "Dr.
Bernstein's Diabetes Solution: A Complete Guide to Achieving Normal Blood
Sugars".
The first articles in the medical literature on
the home blood glucose monitoring were published in 1978
(references 1-5). These demonstrated that patients could reliably measure
their blood glucose levels at home and improve control of their glucose levels. Today, you can find a
blood glucose monitor that can accurately measure levels.
In November 1986, the American Diabetes
Association, the Centers for Disease Control and Prevention, the Food and Drug
Administration, and the National Institutes of Health convened a Consensus
Conference on Self-Monitoring of Blood Glucose. The results of that conference
was that self-monitoring of blood glucose was an exciting and important tool for
effective management of patients with diabetes (reference
6). It was recommended that SMBG be used by patients to accomplish the
following goals:
(a) Keep track of their glucose levels over
time,
(b) Help make day-to-day decisions for managing glucose,
(c) Recognize emergency situations, and
(d) Educate themselves on how to manage their blood glucose levels
SMBG was first used because health care
providers and researchers believed that its use would help with glucose control
and that better glucose control would reduce or prevent diabetes complications.
In other words, if hyperglycemia (too much glucose in the blood) and
hypoglycemia (too little glucose in the blood) could be controlled, people with
diabetes would remain healthier.
This expectation was shown to be true in 1993,
when the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
published results of a large and conclusive study called the Diabetes Control
and Complications Trial (DCCT), which involved patients at 29 medical centers in
the United States and Canada. In this study, SMBG was an important part of the
glucose control strategy.
This study showed that for persons with type 1
diabetes, intensive treatment to keep blood glucose levels close to normal
reduced the rate of diabetic complications. In fact, the risk reduction was 76%
for eye disease, 50% for kidney disease, and 60% for nerve disease.
These benefits of tight control of glucose were
not problem-free however. Patients in the intensive treatment group had an
increased risk of hypoglycemia.
In September 1993 the American Diabetes
Association held a second Development Conference on Self-Monitoring of Blood
Glucose. This conference noted that SMBG was an important component of the
treatment plan of patients with diabetes mellitus and four major reasons for
using SMBG were discussed:
(a) Controlling glucose at a specific, healthy
level,
(b) Detecting and preventing hypoglycemia, and severe hyperglycemia,
(c) Adjusting care in response to changes in life-style for individuals
requiring medication, and
(d) Determining the need for starting insulin therapy in gestational diabetes
mellitus (temporary diabetes that happens during pregnancy).
Currently, the market for blood glucose meters
is several billions dollars per year worldwide and growth continues.
References
1. Danowski TS and Sunder JH: Jet injections of insulin during self-monitoring
of blood glucose. Diabetes Care 1:27-33, 1978.
2. Skyler JS et al: Home blood glucose
monitoring as an aid in diabetes management. Diabetes Care 1:150-157, 1978.
3.Sonksen PH, Judd Sl, and Lowy C: Home monitoring of blood glucose- method for
improving diabetic control. Lancet 1: 729-732, 1978.
4. Walford S et al: Self-monitoring of blood
glucose -- improvement of diabetic control: Lancet 1: 7320735, 1978.
5. Peterson et al: Feasibility of tight control
of juvenile diabetics through patient-monitored glucose determinations. Diabetes
27(suppl 2): 437, 1978.
6. Ikeda Y et al: Pilot study of
self-measurement of blood glucose using the Dextrostix-Eyetone system for
juvenile-onset diabetes. Diabetologia 15:91-93, 1978.
(From the Food and Drug Administration)
See also
Blood Glucose, Glucose
Note:
This diabetes
health education project is supported
by Chong's Health Care at http://www.cljhealth.com, one of the leading companies in the discovery of
alternative
medicines for diabetes.
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