Understanding Home Blood Glucose Meters


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.

  1. 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.
  2. 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.
  3. 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. 

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Updated June 2002
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