Home-Use Tests - Glucose
Basic Information
What does this test do?
This is a home-use test kit to measure blood sugar (glucose)
in your blood.
What is glucose?
Glucose is blood sugar that your body uses as a source of energy.
Unless you have diabetes, you body regulates the amount of glucose
in your blood. People with diabetes have poorly-controlled blood
glucose.
What type of test is this?
This is a quantitative test -- you find out the amount of glucose
present in your sample.
Why should you do this test?
You should do this test if you have diabetes and you need to
monitor your blood sugar (glucose) levels. You can use the results
to help you
- determine your daily adjustments in treatment,
- know if you have dangerously high or low levels of glucose,
and
- understand how your diet and exercise change your glucose
levels.
The Diabetes Control and Complications Trial (1993) showed that
good glucose control using home monitors led to fewer complications.
How often should you test your glucose?
Follow your doctor's recommendations about how often you test
your glucose. You may need to test yourself several times each
day to determine adjustments in your treatment.
What should your glucose levels be?
Your fasting blood glucose level (after not eating for 8-10 hours)
should be lower than 126 mg/dL. Your blood glucose level immediately
after eating should be lower than 200 mg/dL.
How accurate is this test?
The accuracy of this test depends on many factors including:
- the quality of your meter.
- the quality of your test strips.
- how well you are trained to do the test.
- your hematocrit (the amount of red blood cells in the blood).
If you have a high hematocrit, you may test low for blood glucose.
Or, if you have a low hematocrit, you may test high for glucose.
If you know your hematocrit is low or high, discuss with your
health care provider how it may affect your glucose testing.
- interfering substances (some substances, such as Vitamin
C and uric acid, may interfere with your glucose testing). Check
the package insert for your meter and test strips to find out
what substances may affect the testing accuracy.
- Altitude, temperature, and humidity (high altitude, low and
high temperatures, and humidity can cause unpredictable effects
on glucose results). Check the meter and test strip package
inserts for more information. Store and handle the meter and
strips according to instructions.
How do you do this test?
Before you self-monitor your blood glucose, you must read and
understand the instructions for your meter. In general, you prick
your finger with a lancet to get a drop of blood. Place the blood
on a disposable "test strip" that is coated with chemicals
that react with glucose. Then place the test strip in your meter.
Some meters measure the amount of electricity that passes through
the test strip. Others measure how much light reflects from it.
In the U.S. meters report results in milligrams of glucose per
deciliter of blood or mg/dl.
You can get information about your meter and test strips from
several different sources including the toll free number in the
user manual or the manufacturer's web site. If you have an urgent
problem, always contact your healthcare provider or a local emergency
room for advice.
How do you choose a Glucose Meter?
You can purchase more than 25 different types of meters. They
differ in several ways including
- amount of blood needed for each test
- how easy it is to use
- pain associated with using the product
- accuracy
- testing speed
- overall size
- ability to store test results in memory
- cost of the meter
- cost of the test strips used
- doctor's recommendation
- technical support provided by the manufacturer
- special features such as automatic timing, error codes, large
display screen, or spoken instructions or results
Talk to your health care practitioner about glucose meters and
how to use them.
How do I compare my home test glucose values with the laboratory
values?
Most home blood glucose meters in the U.S. measure glucose in
whole blood. Most lab tests, in contrast, measure glucose in plasma.
Plasma is blood without the cells. A lab test of your blood glucose
will be about 10-15% higher than the value given by your meter.
Look at the instructions for your meter to find out if it gives
its results as "whole blood" or "plasma equivalent."
Many meters now sold give values that are "plasma equivalent,"
which means they can be compared more directly to lab test values.
Should you use generic or "third party" test strips?
You may choose test strips that are made by a different company
than the one that made meter. Sometimes, generic test strips are
cheaper. If you choose generic test strips
- make sure the generic strips will work with your meter. Check
the label of the test strips to make sure they will work with
the make and model of your meter. Just because the generic test
strip looks like it will work does not mean that it will
work.
- watch for inconsistent results. If you get poor results,
try strips made or recommended by the maker of your meter until
you again get consistent results.
How can you check your meter's performance?
There are two ways to make sure your meter works properly:
1. Use liquid control solution
- every time you open a new container of test strips
- occasionally as you use the container of test strips
- whenever you get unusual results
You test a drop of these solutions just like you test a drop
of your blood. The value you get should match that written on
the liquid control solution bottle.
- Use electronic checks. Every time you turn on your meter,
it does an electronic check. If it detects a problem it will
give you an error code. Look in your owner's manual to see what
the error codes mean and how to fix the problem.
- Compare your meter with a laboratory meter. Take your meter
with you to your next appointment with your health care provider.
Ask your provider to watch your technique to make sure you are
using the meter correctly. Ask your healthcare provider have
your blood tested with a routine laboratory method. If the values
you obtain on your glucose meter match the laboratory values,
then your meter is working well and you are using good technique.
What should you do if your meter malfunctions?
If your meter malfunctions, you should tell your health care
professional and the company that made your meter and strips.
Can you test blood glucose from sites other than your fingers?
Some new meters allow you to test blood from the base of your
thumb, upper arm, forearm, thigh, or calf. If your glucose changes
rapidly, these other sites may not give you accurate results.
You should probably use your fingers to get your blood for testing
if any of the following applies
- you have just taken insulin
- you think your blood sugar is low
- you are not aware of symptoms when you become hypoglycemic
- the site results do not agree with the way you feel
- you have just eaten
- you have just exercised
- you are ill
- you are under stress
Can you test blood glucose without a needle stick?
Researchers have been trying to find ways to test glucose without
finger sticks, but none are available yet.
Some new methods may make it easier for some people to monitor
their glucose levels between finger sticks, such as
Cygnus GlucoWatch Automatic
Glucose Biographer or
the MiniMed Continuous Glucose
Monitoring System (CGMS).
Several reports in the literature describe methods where you
shine a beam of light on the skin and interpret the way the glucose
under the skin responds to the light. FDA has not yet approved
any of these methods.
Where can you get more information about glucose and glucose testing?
Safety Tips
Glucose Meter Test Results: Useful Tips to
Increase Accuracy and Reduce Errors
Have you ever wondered why you got a bad glucose meter test result
when there is nothing obvious wrong with your meter, your test strips
are new, and you’ve been running glucose tests for years?
The simple answer is that glucose meters are not perfect, and neither
are the people who use them! This chart lists some tips to help
you get the most accurate results from your glucose meter.
| Make
sure you... |
Because |
- follow the user instructions about sample size. Repeat
the test if you have any doubt that enough blood was added.
|
If there is insufficient blood on the test strip,
the meter may not be able to read the glucose level accurately.
Although many meters are designed to alert you when the sample
size is too small, some meters detect only large errors. There
have been cases where meters have displayed glucose levels that
were less than half the actual levels without displaying error
messages. |
- insert the test strip completely into the meter guides.
|
When a test strip is not fully inserted into
the meter, the meter cannot read the entire strip area. Many
meters are designed to detect strip placement errors and will
not provide a result. But, just as described above, many meters
detect only large problems. There have been cases where meters
have displayed glucose levels that were significantly higher
or lower than the actual levels when there was only a small
error in strip placement. |
|
Even small amounts of blood, grease, or dirt
on a meter’s lens can alter the reading. |
- check the test strip package to make sure the strips are
compatible with your meter.
|
Test strips are not always interchangeable, and
meters cannot always detect incompatible strips. Test strips
that look alike may have different chemical coatings. Small
variations in strip dimensions can also affect results. |
- check the expiration date on the test strips.
|
As a test strip ages, its chemical coating breaks
down. If the strip is used after this time, it may give inaccurate
results. |
- enter the correct calibration code from the outside of
the strip bottle each time you run a test (if applicable).
|
Results can vary significantly between manufactured
lots of reagent strips; the calibration codes help the meter
compensate for these variations. |
- run quality control as directed.
|
Running quality control is typically the only
way to know when test strips have gone bad. Test strips do not
always last until the expiration date on the bottle. This may
be because the manufacturer has over-estimated the dating or
because the cap was not replaced promptly after use. |
- check the results from your meter against laboratory results
as often as possible.
|
Over time, test systems can drift apart. Since
results from either test system maybe used to treat your patients,
it is important for the systems to remain synchronized. |
- question results that are not consistent with physical
symptoms. If a test result seems wrong, have a blood sample
tested by the main laboratory.
|
There may be many reasons why a test result is
incorrect. In addition to the items above, some physiological
conditions such as dehydration, hyperosmolarity, high hematocrit,
or shock may significantly affect test results. |
Common Problems with the Use of Glucose Meters
Glucose Testing Tips:
Diabetes care has come a long way since the introduction of insulin
and the first oral anti-hyperglycemic medicines. Life span and quality
of life have improved for majority of affected individuals. Even
better, a large part of diabetic care formerly performed in hospital
clinics can now be managed at home with use of well designed home
based glucose meters, a telephone and a good patient-doctor relationship.
The Office of In Vitro Diagnostics (OIVD) is charged with the job
of evaluating many devices, including glucose meters. OIVD helps
these meters come to the public market. Another of its tasks is
the continuous evaluation of the same devices for long term safety
and effectiveness not just of the devices, but of how the devices
are used.
OIVD is taking this opportunity to provide some friendly tips in
Point of Care glucose testing inspired by some comments we have
received from manufactures and users of these devices.
Causes of false results may be patient/sample based or user/device
based. Some common problems and their effects on meter glucose readings
are listed below.
Problem |
Results |
Recommendation |
| Sensor strips not fully inserted into meter |
false low |
always be sure strip is fully inserted in meter |
| Patient sample site(for example the fingertip)
is contaminated with sugar |
false high |
always clean test site before sampling |
| Not enough blood applied to strip |
false low |
repeat test with a new sample |
| Batteries low on power |
error codes |
change batteries and repeat sample collection |
| Test strips/Controls solutions stored at temperature
extremes |
false high/low |
store kit according to directions |
| Patient is dehydrated |
false high |
stat venous sample on main lab analyzer |
| Patient in shock |
false low |
stat venous sample on main lab analyzer |
| Squeezing fingertip too hard because blood is
not flowing |
false low |
repeat test with a new sample from a new stick |
| Sites other than fingertips |
high/low |
results from alternative sites may not match
finger stick results |
| Test strip/“Control” solution vial
cracked |
false high/low |
always inspect package for cracks, leaks, etc. |
| Anemia/decrease hematocrit |
false high |
venous sample on main lab analyzer |
| Polycythemia/increased hematocrit |
false low |
venous sample on main lab analyzer |
The advantage of Point of Care testing is eliminated if proper
technique is not followed. In addition to the above recommendations,
laboratory professionals must remember to wash hands and change
gloves between patients. Also, clean the surface of the meter if
blood gets on it. This each time, every time approach helps
protect both the patient and the health care worker from blood borne
agents like HIV and HCV.
All operators, from patients to non-lab health care workers to
medical technologists and physicians, should be thoroughly familiar
with any device prior to using it. The best way to do this is to
read the package insert and user manual carefully before
using a device for the first time. It sounds simple, and it is.
If you have any questions, ask someone who is familiar with the
device. Another option is calling the customer service telephone
number located on most package inserts. The people on the other
end are there to help. Another good tip is to reread the package
insert every few months. It is a good practice and their may be
changes.
Next, watch an experienced laboratory professional, doctor, nurse
or diabetic educator perform the test. Then perform the test in
front of someone who has experience in using the glucose meter and
instructing others on its performance. Ask for tips.
Specific problems come up from time to time including glucose readings
that don’t make sense. For example you might feel fine when
the glucose meter reading is obviously too high or too low. Remember,
the best way to resolve any questionable result, and the best sample
from any sick patient, is still a venous blood sample tested at
a central lab. Even then any result that does not fit the clinical
picture needs to be investigated and, at a minimum, repeated.
For more information also see FDA’s diabetes website at:
http://www.fda.gov/diabetes/
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