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Introduction
After reading this article, you will understand how home blood glucose meters
are regulated, know that they are accurate, and feel comfortable using them as a
monitoring tool for your diabetic pet.
Home glucometers have revolutionized diabetes care for humans. Many pet owners
also find them indispensable in managing the care of their diabetic cats and
dogs. Meter manufacturers are quick to state that veterinary use has not been
validated, so their reliability on pets is unknown. No home glucometer is presently FDA approved for veterinary use. But there are many vets who
are now using glucometers and support home use of these devices.
If you are using a glucometer to manage your pet's diabetes, you should
understand what the readings mean. And
you should always discuss home monitoring with your vet for guidance before
basing any insulin changes on home meter readings.
Who Makes Sure Meters Are Accurate?
Manufacturers' claims of accuracy vary widely. The Food and Drug
Administration (FDA) oversees the manufacture and use of home meters in the
United States, and sets standards which the makers must meet. The American
Diabetic Association (ADA) has even stricter standards but these are not legally
binding. Canada and other nations
have their own guidelines and regulations. If you are outside the US, please
refer to your nation's regulatory agency for specifics. Although an
international standard has been discussed, none has been adopted to date.
In this discussion we are referring to meters bought and used within the
US.
To help insure quality control, the FDA requires that each meter have it's own
serial number, so problems can be traced, "from birth to death" of the
meter. Your meter should have a serial number printed on the back.
Most makers offer a 24 hour toll free "help line" and the phone
number should be on the back of the meter, or in the printed material that came
with your meter. Don't hesitate to call if you are having trouble with your
meter or have questions. Many issues arising from consumer questions and
complaints have resulted in major improvements in meter design and function, so
don't be afraid to speak up.
Where Information In This Discussion Came From
This discussion is limited to a few specific home meters
listed below. These meters were chosen for review because they have test strips
using capillary action to "suck" the blood into the meter. Many owners
of diabetic pets have found this type of meter, in particular the Elite by
Bayer, to best meet their needs. Meters
that are not included on this discussion are not “bad” meters, they are just
not commonly used by owners of diabetic pets.
- Glucometer Elite made by Bayer
- Glucometer Dex by Bayer
- Fast Take by LifeScan
- Accuchek Advantage by Roche
- Precision QID by Abbot
Information about a particular meter's accuracy was
obtained from technical representatives of the manufacturers by phone calls to
their help lines in October 1999. The
accuracy claims made by the individual company representatives are not backed by
any proof here. Each of these meters are held to an FDA standard which some
claimed to beat.
Comparing Your Meter Value To The Value The Vet
Gets
Before we discuss accuracy, you should be aware that a blood glucose
(bg) analysis done by your vet on high quality lab equipment differs from the
blood sample used by a home meter. There can be a difference in readings between
the two because each uses a different type of blood sample. Home meters use
whole blood (cells and fluid) obtained from capillaries. Labs measure glucoses
using the plasma or serum portion of venous blood.
This means that only the fluid portion of the blood is tested, after the
red blood cells and some other blood components are removed. This difference can
be important since whole blood values (used with home meters) will be somewhat
lower than plasma values. There is a conversion factor to account for the
difference that may need to be made before you can compare results. Because of
the confusion this causes consumers in interpreting results, some home metering
systems, especially the newest ones on the market, have adjusted their strips to
calculate this into the reading you'll get. Corrected strips will clearly state
that they're adjusted to plasma values somewhere on their packaging.
If you're using a meter and strip system that does not correct to reflect plasma
values, just remember that your meter reading will probably be a little lower
than the actual lab value would be, and may read lower than a system that
automatically makes the adjustment.
In case you're getting nervous about all this math, relax.
You do not need to do any of these conversions.
You just need to understand what the numbers your meter gives mean. Home
meters are not designed to be diagnostic devices but they are extremely useful
in monitoring trends and detecting hypo events or elevated bgs that may point to
a need for changes in some aspect of diabetic care.
Even though your meter results may not match your vet’s results, they
should be close enough for your purposes of achieving and maintaining
regulation.
In regard to specific meter systems, Elite, Dex, Fast Take and Precision are
already corrected to plasma values. Accuchek Advantage is corrected if you are
using the Comfort Curve strips with serial numbers between 522-533. (All
Comfort Curve strips will eventually be adjusted.)
What this means is that if you were to have a blood sample drawn for bg
analysis by a lab (and it was processed within 30 minutes) and also checked your
meter reading at the same time, the results should be pretty much the same. A
lab value of 100 mg/dl should also
read "about" the same value by your meter even though the lab uses
plasma and the meter uses whole blood. This is taken into account by the meter
test strips. We'll get to what "about"
means in a bit.
If at all possible, you should compare your glucometer results with a lab
analyzed specimen once or twice a year. You can check your meter against the lab
value your vet gets the next time he/she draws serum glucose levels. Or check it
on yourself if you're having blood work done that includes a serum glucose.
Obtain the sample for your meter just as you would do at home doing a skin
prick.
Some things that you should remember about home monitors is that consistency of
results is variable. You will never get exactly the same results from one sample
to the next, even using the same machine and the same blood draw.
You can't compare results from two different meters unless you know that
they are calibrated in the same way. And
thirdly, different meters are better at different ranges. Some are more accurate
at low ranges, while others do a better job with the mid or higher ranges.
Despite these limitations, they are still valuable in gauging relative blood
sugars and trends. It's also very important that you calibrate your home machine
regularly as specified by the manufacturer to make sure your meter is
functioning correctly.
Accuracy of Home Glucometers
The accuracy of results depends on the capabilities of the meter, how
you perform the test, and how you care for your machine and strips. So take the
time to read the manual supplied with your meter, become familiar with using
your meter, and care for it properly.
What does “accuracy” mean?
Once whole blood results are calibrated to plasma, home glucometers are
considered accurate by the FDA if their reading falls within a 20% variance in
either direction of a lab analyzed specimen taken at the same time.
We'll show how this works below. The FDA has allowed these seemingly
large variances because meters are not meant to be diagnostic devices but simply
monitors which are held to less stringent standards than more costly and precise
lab equipment. The manufacturers also claim the cost of more accurate equipment
would put them out of the home diabetic market that has used them to great
benefit. The meters may be more accurate than +/- 20%, but they must
meet this minimum standard. One manufacturer claims even better accuracy with a
variance of only 5% .
How much your meter reading may vary from the lab result depends on the brand of
meter you use. Your meter can
provide accurate results only if you performed the test using the proper
techniques and the meter is properly calibrated according to the instructions in
the user manual.
There is no way to correctly adjust a meter reading to a lab value because of
the large degree of variance in meter readings. Just remember that
"accuracy" can be a relative thing, but the degree of accuracy you can
expect from your meter will be good enough for the purpose of monitoring your
pet’s diabetes at home.
Accuracy of specific meters
- Elite and Dex models by Bayer
have the least variance according to information provided by its rep. Bayer says
their meters are within 5% of the real lab value. This is excellent in
comparison to the other models mentioned above.
What this means is that if the lab value is 100 mg/dL an Elite (or Dex) meter
will give a reading in the range of 95-105 mg/dL. The math is very easy: 5% of 100 is 5, so the
range
of accuracy is 100 plus or minus 5 mg/dL.
A lab bg of 300 mg/dl should read between 285-315 (5% of 300 is 15, so 300
+/- 15 mg/dl) on an Elite.
-
FastTake and Precision have a 20% variance
according to their reps, so a lab value of 100 mg/dl can read 80-120 (100 +/- 20
mg/dl) on your meter. If the lab value is 300, the FastTake will register
between 240-360 (300 +/- 60 mg/dl).
- Accuchek Advantage has claims a 20% variance on
lab values above 100 mg/dl but drops to 15% for lab values 100 and below. So an
Accuchek Advantage may read between 85-115 mg/dl when the actual lab value is
100. At a lab value of 300, the Advantage will read between 240-360.
If you look closely at the examples, you'll see that this variance can mean a
large difference in the higher bg values (a 120 mg/dl range at a lab value of
300 for Fast Take). At lower bg values, the range decreases accordingly (a 40
mg/dl range at a lab value of 100 on Fast Take). Although this might seem like a
wide variation, it still just represents a 20% difference above or below the lab
analyzed reading and should not be a cause for serious mistakes in managing the
disease. At bgs levels indicating hypoglycemia, which are most likely to cause
immediate concern and danger to a diabetic, the actual numeric range of variance
becomes quite narrow, even if a variance of 20% is expected.
For those of you Math Wizards interested in comparing a lab
derived bg value to a meter reading using strips that aren't calibrated to
plasma values, you'll need to convert the whole blood value before you can
calculate the variance range. First,
either divide the lab value by 1.12 or multiply it by 0.89, either way will give
about the same result. In this way a lab value of 100 mg/dl becomes a corrected
value of 89 mg/dl. Then do the
calculations for variance as above.
Comparing Lab Values to Values Obtained With An Elite
or Dex
Since the Glucometer Elite is widely used by owners of diabetic pets, the
following info (provided by Bayer in Oct. 1999) may help you and your vet get a
better understanding of what glucometer readings may mean when comparing Elite
readings to vet drawn and lab analyzed serum glucose values.
The following information can also be used for the Glucometer Dex
Testing should be done using both methods (lab and meter) at or about the same
time -no more than a few minutes apart at most. The lab sample should be
analyzed within 15-20 minutes of collection. The Elite values are based on plasma serum.
- Plasma venous sample versus whole blood capillary sample
(lab versus skin prick) This is the recommended method of checking meter accuracy
against lab values. If you compare a vein sample sent to a lab to a capillary
sample from the Elite, they should be very comparable.
- Plasma venous sample versus whole blood venous sample
(lab versus Elite reading using vet drawn blood for both
tests).
If you compare a vein sample sent to a lab to a vein sample
tested on the Elite, the Elite should be 7% higher.
- Plasma venous sample versus whole blood capillary sample on
the same meter (Elite versus Elite). If
you compare a vein sample done on the Elite to a capillary sample done on the
Elite, the venous sample on the Elite will be 7% higher than the capillary
sample on the Elite.
Since all home glucometers are not diagnostic devices but
simply monitors, don't expect your meter results to exactly match the lab
results. If both the lab equipment and your meter are accurately calibrated and
the testing technique has been performed correctly, they should be close, with
the Elite reading 5-15% higher or lower than the lab result.
A Practical Example
To provide another example of accuracy and variance more briefly,
let's answer this edited question posted to the petdiabetes list:
"I have a question I was wondering if anyone has encountered. I have been
using a glucose meter on my diabetic cat. I tested him this morning and got 288.
The site where I did the prick was bleeding more than usual and I decided to
experiment and so I did a second test strip. This second test strip came back
with results of 364. They were only
taken minutes apart. I seemed to have about the same coverage of blood on both
sticks. Am I doing something wrong?????"
In all likelihood, probably not.
Without knowing the specifics of the meter, by FDA regulations, meters shouldn't
vary more than 20% (in either direction) of what your meter reads (after
adjusting to reflect plasma values) and what the lab value would be on blood
drawn and processed at the same time under ideal conditions.
Assuming this 20% variance (in a sample already corrected for plasma values):
-If the lab value were 320 mg/dl, the meter could give you a number
(or +/- 64 mg/dl) and still be considered accurate.
-At a theoretical lab value of 320 mg/dl, your meter reading is
"accurate" if it reads 20% less than or more than 320 mg/dl.
So any value between 256-384
would be considered accurate, and that could account for results of 288 and 364
on the same blood using the same meter.
This is NOT to say that your cat's
"real" bg is 320. That figure
was selected because it fits the question. To determine if there is a problem with your meter,
a venous blood sample would also need to be analyzed at the same time by a lab
and the numbers could be compared.
What Should I Do If I think My Meter Is Giving
False Readings?
First of all, look at your pet! Especially if you're getting readings
in the low ranges. If you notice any signs of hypoglycemia like lethargy,
confusion, inattention, shakiness or coordination problems, grab your Karo,
honey, etc. and treat for
hypoglycemia. Continue to observe your pet, and worry about your meter
when it is safe to do so.
If Fluffy or Fido looks fine, then go through this checklist of common user
errors:
- Was the blood sample large enough to cover the strip’s
test area completely?
- Was the strip handled and stored properly? Some strips
can't be touched in the sampling area or are sensitive to humidity and
temperature extremes. Always keep the vial tightly sealed, opening it only long
enough to remove the strip you need. Open an individually foil-wrapped strip
just before using, and use it promptly. If
you'll be taking your meter and strips with you in the car, be sure they won't
be subject to high temperatures if locked inside on a warm or sunny day.
Remember, it can be in the 70-80 degree range outside, but the inside of
you car can get very hot, very quickly.
- Are the strips expired?
- Are the strips the right kind of strips for your meter?
Each manufacturer has several models of glucometers, each using a different type
of strip. Make sure you're using the right strip for your meter.
- Does the code from the strip container match the number
coded into the machine? This is a common mistake. You should never transfer
strips from one container to another as the lot numbers will probably be
different.
- Is the meter dirty?
- Has the meter been dropped?
- Was the meter stored at very high or very low temperatures?
Check your manual or call the maker if you aren't sure what this will do to your
meter if it happens.
You should then perform the quality control checks
specified in your meter manual. Make sure you use solutions that are not
outdated, The expiration date should be clearly marked on the bottles. Again, if
you're not sure how to do this, call the company.
If everything checks out, perform another blood sampling using your best
technique. If you still have doubts about accuracy, call the manufacturer. But
if you have gotten two low readings in the hypoglycemic range, assume the result
is accurate and treat for hypoglycemia first, even if your pet is not showing
symptoms, then call your vet for more guidance if needed. Many pets may not show
any visible signs of hypoglycemia , even at very low bg levels (asymptomatic
hypoglycemia). So please err on
the side of caution and treat for hypoglycemia.
Other factors that may affect bg
readings
There are many things beyond your control that may effect the accuracy of your
readings depending on the type of meter you use. Elevated hematocrit levels (caused by dehydration or other
conditions), large doses of Vitamin C, high blood
oxygenation levels, poor circulation, even altitude has been noted incidentally
as causing errors in home glucometer readings in humans. If you have questions
about factors that may be affecting your results, call the manufacturer. Today's glucometers are pretty accurate if you take the time to perform
the testing properly and maintain your machine in good working order.
Meter Maintenance
Be sure to follow the routine calibration procedures recommended for your
meter. This is important to insure your meter is working properly. This routine check of meters
is so important that a built in timer to shutdown meters poorly maintained by
owners is being considered for future development. Be sure to calibrate
your meter every time you change test strip lots or have other concerns about
the meter's function (like if it's been dropped).
Some people have tried to cut test strips in half to save money, Don't! You'll
be wasting money instead and your test results, if any, will be invalid.
Issues Involved In Using Older Meters
Sometimes owners are offered a free older meter by a person who no
longer needs their bg meter. The
first thing people ask when they are given an older meter is whether or not they
should or can use it. A lot depends
on how old it is and how it's been handled and stored. The first thing you will
want to do is check with your local pharmacy and see if the test strips are
still available for that particular meter. If they are no longer available, you
can not use that meter. If test
strips are available and the meter is in good condition (has been handled and stored
properly), see if you can get replacement batteries and new quality control
solutions for the meter, and do so.
Meters will become less reliable over time, so doing quality checks (with fresh
solutions!) becomes even more important. Don't use the solutions that came with
the old meter if they are outdated or have been open a while. If the quality
checks are okay, the meter should be safe to use.
If the meter is more than a few years old, you may want to think about
purchasing a new model or using the old meter as a trade-in. Since meter
companies make their profits on the strips, new meters can be obtained for
little if any cost, especially if you look into the trade in and rebate offers
that abound. You can use the old meter as a trade in if the person who gave it
to you doesn’t want it back and if it meets the trade in terms of the
manufacturer.
Meters have become much easier to use in the last few years and more foolproof.
Many of the new meters use the test strips that use capillary action to
draw the blood into the test strip, and they require only a tiny drop of blood. The older meters are usually “drip on” type test strips,
and they require a larger drop of blood. Since many of the newer systems are
correcting for plasma values, the results are easier to understand and compare
to results from a lab, and this might be a concern for you. Many newer models
have added features like built in memory for storing results, and faster test
times.
Contacting the Manufacturer
Your meter's manufacturer should be able to answer any question about
its function and use and many are quite willing to supply detailed written
information to consumers. Because veterinary use of glucometers
is not regulated or approved, they may be reluctant to discuss things in terms
of your pet. If you need to know more about your meter and how to use it or are
having problems, don't let this stop you from calling. Let them talk about
humans if they want to, the principles you're interested in will still apply.
If your meter doesn't have a toll free contact number printed on it's back, you
can reach the following manufacturers, listed alphabetically, here:
-
Bayer Diagnostics - (Glucometer Elite and Dex) 1-800-348-8100
- Life Scan - (Fast Take) 1-800-227-8862
- Medisense (Abbot) - (Precision) 1-800-527-3339
- Roche - (Accuchek) 1-800-858-8072
Web Resources
- Children with Diabetes
discusses and evaluates many meters in terms of ease of use by and for children.
A nice site for comparing features of models you may be considering buying for
use on a pet.
- American Diabetes Association (ADA)
General diabetic info for humans and a page or two for pets.
- From LifeScan:
For an online calculator for the difference between whole blood and plasma values.
- US Food and Drug Administration (US FDA)
For issues relating to meter regulation and standards in the US:
Note: If using this site or other technical or medical sites geared
toward clinicians, use SMBG (Self Monitored Blood Glucose) the acronym used for
home glucometers, as a basis for your search.
This information was compiled and written by Chris,
who is a registered nurse and has a diabetic dog.
 
Updated June 2002
Copyright. All rights reserved.
This site is for information purposes only. Please consult
your veterinarian. |
Understanding Home Blood
Glucose Meters