Inaccurate Blood-Glucose Readings Can Be Caused By A Number Of Factors

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If you have diabetes, your blood-glucose meter is a critical tool that gives you the necessary insight as to what’s going on inside your body at a given moment—an absolutely essential piece of knowledge, particularly if you use insulin.

That’s why it’s important to ensure that your meter is functioning correctly and giving you accurate readings.

Start by periodically using a glucose solution provided by your meter’s manufacturer to test the accuracy of the results you’re getting.

And watch out for these factors that can affect your meter readings:

  • Outdated test strips.
  • Incompatible test strips. It’s actually possible with some meters to insert a strip that is not meant to be used with that meter.  This can be a problem if you buy strips that are manufactured by another company; while test strips from non-meter manufacturers are usually fine, be sure that you’re buying the strip that that is made for your meter.
  • Substances on your hands. For example, substances on the finger used for lancing, even a small amount that can’t be seen, may cause a high blood-glucose reading.
  • Temperature changes. Your meter’s user’s manual (or web site) will tell you the temperature range in which your meters will function correctly.
  • Wet fingers. Fluid mixing with blood may cause an inaccurate reading.

So, with these potential problems in mind, the Certified Diabetes Educators in the clinic at Joslin Diabetes Center recommend following these steps in testing:

  • Before using the meter for the first time and again every few weeks, check your meter using the control solution.  Once opened, the control solution is only good for three months. Label the control-solution bottle with the date when you opened it.  Check the date and shake the control solution before using it. The value of the control solution should be in the target range printed on the strip’s container.
  • Make sure the strips are not expired. Check the date on the strip container.
  • Calibrate! Make sure the code on the strip container matches the code on the meter.
  • Wash your hands in warm water and then dry them well.
  • Massage your hands before checking.
  • Select a site on one side of the center of a fingertip.  Rotate sites for each check.
  • Apply gentle pressure to a lanced finger to help the drop of blood form on the surface.
  • Fill completely the strip’s target area with blood.

It’s important to get the most accurate meter reading when checking your blood-glucose levels. Knowing what can affect a reading will help ensure that your meter produces the most accurate output.

For more information:

  • Click here for more information on diabetes and blood glucose.
  • Click here for more on diabetes management.
  • Click here for Joslin Diabetes Center videos.
  • Click here to learn about Celtics’ star Ray Allen’s $3 for 3’s fundraiser for the Joslin Diabetes Center’s High Hopes Fund.
  • Click here to learn more about Joslin Diabetes Center.

12 Responses to Inaccurate Blood-Glucose Readings Can Be Caused By A Number Of Factors

  1. Doris J. Dickson says:

    Could please admit that these machines are not accurate not matter how well behaved the patient is. They are allowed to be 20% inaccurate by the FDA and they are.

    The best thing to do is to take your meter with you when you have a regular lab glucose (not versus a doctor’s office meter) done. Try to have your BS in target (85-100) since inaccuracies vary substantially from the low end to the high end – as I’ve heard manufacturers say “because highs don’t matter”! Idiots. They do matter.

    We can’t fix the meter or calibrate the meter but we are better armed with know the potential range of inaccuracy and in my experience – manufacturers take advantage of very inch of that 20%.

    I look forward to the day the FDA finally puts their foot done and says enough. Why should we have pumps accurate to the .xx unit when we can’t get an accurate blood sugar reading. And at $1-1.50 per strip they’ve got plenty of money to do R&D to fix them! Would NASA accept 20% inaccuracy? No, so why should patients have to put up with it.

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  3. Karen says:

    My main problem is tracking down control solution for me meter (the Accu-Check Compact Plus). I have the hardest time finding a store / pharmacy in my area that stock it – even though they all sell the meter. I suppose I need to just order it on-line. To be honest, I just make sure I test my blood sugar when I have my labs drawn and make sure the numbers are close. I know I should be verifying my meter’s accuracy more often than that – but the fact that I can’t purchase my control solution is pretty frustrating!!

    • Doris J Dickson says:

      I’ve done the lab test to meter test with several meters – they’re not close. They’re in FDA tolerance but that’s not good enough for tight control like I target (85).

      On top of that, the inaccuracy rate varies based on where your BS is. Low is xxx% inaccurate, normal (85-100) is another and > than that the less they care. You see they maintain only lows really matter so if you’re 200 or 250 it doesn’t matter. Of course if you’re trying to do a correction calculation it does matter!

  4. patrice says:

    Those are all good recommendations from Joslin re: the correct way to test your BS to get accurate results…HOWEVER,,,,when you test 10-15x per day, and many of these are before driving, at work, in the supermarket, etc….its impossible to wash/dry your hands. Also, your fingers really don’t have enough places to rotate to if one is testing as much as I do. Using alternate sites doesn’t always work.
    I agree with Doris and Karen’s comments re: accuracy of meters and availability of control solutions
    Testing has come so far, and yet has so far to go.

    • Doris J Dickson says:

      No kidding Patrice … I too test 15 times a day. No alternate sites for me… I want the least inaccurate test I can get. And I want all my tests to be apples to apples and if you start moving around, they won’t be.

      One thing I have done (since the Joslin taught me it in the 70’s) is using my earlobes. They caught the blood in a long skinny tube. It was kinda cool. It is still capillary blood but since it changes the distance to the heart and therefore it’s timing accuracy, I don’t know if it’s is as accurate as my fingers.

  5. Mary Murphy says:

    Got one of these meters free I don’t mind buying the strips..I have got 3 boxes and the machine is not accurate…made 2011…only got it last year..2016..what can I do now.

  6. James says:

    Bought some cheaper off brand strips .
    Used them for three weeks and they showed an elevated level almost 50 more registered. From what use to be a high after meals of 180 to 230…..
    When i bought the correct strips they reported in the morning 97; and after a big lunch 158 high.
    Using the right and recommended strips eased a lot of fears.

  7. David Lawrence says:

    Just to be clear, a 20% variance means +/- 20%. That means a 180 reading could mean my blood sugar is anywhere between 144 and 216. Pick a value. Add to that cheaper strip variance (since I test so often) and my meter is basically useless. I have two meters and a dexcom, and I don’t trust any of them.

    FDA, get off your asses and do something about this!

  8. Patrick says:

    As I read the comments, and I hear the frustration, there is one thing that I don’t hear, and that is anyone that is willing to spend 12-20K on their home test equipment. I have been a diabetic for 25 years and the ability to home test has greatly improved in both accuracy and cost. But our home is not a lab environment and your home test equipment is not lab quality equipment. You are spending $40 for a glucometer and $.50 for a test.

    +/- 15% is pretty good considering that you are in an uncontrolled environment and you are testing capillary blood, not arterial blood. The blood is sitting on the tip of your finger that is not sterile and oxidizing as you are fiddling with your meter. Do you know if your meter is plasma calibrated or whole blood calibrated (yes, that makes a difference too).

    Protect your test strips, they are the most vulnerable part of the testing process. They are made with an organic enzyme that degrades over time and are especially vulnerable to heat and humidity. There is a use by date on the box and a recommended amount of time to use the strips up after the vial has been opened and exposed to the environment, usually 90-120 days.

    You need to use your glucometer as a tool along with other tools, such as how you feel and knowing your body and how it is affected by the foods you eat and the stress of the day to make decisions on medication and diet.

    Check your meter readings against your A1C each quarter to know if your meter tends to read higher or lower. Talk to your diabetes educator. Keep up with the latest technological breakthroughs.

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