Blood Glucose Meter Accuracy – Why Do My Results Differ?

accuracy diagramBlood Glucose Meter Accuracy is one of the most frequently asked questions I receive as the editor of this site. Why does my monitor give one result, then a completely different result 2 minutes later? How come meter X gives a different reading than meter Y? Why is my home meter reading different than the one I get at the lab? There are many different questions, but they all boil down to why any given glucose monitor gives a wide variation of results.

Well, this article is going to cover this question once and for all. Admittedly, this article is in my own self-interest. I am getting tired of responding to all the questions! Now, I can simply refer people to this article.

There are two main reasons a glucose meter provides varying results, either user or mechanical error, or the inherent limited nature of the meter itself. This second issue we will address by looking at the certification process used by the FDA.

Let’s look at user or mechanical error first.


As you will notice from the list below, many inaccurate readings can be the result of user or mechanical error. The key take away here is read the user manual, not just the “quick start guide” and follow the guidelines. There are many possible reasons for error; these are some of the more common ones.

Broken Meter: Let’s get this one out of the way. It is unlikely the meter is broken, but it does happen.

Personal Hygiene: Your hands and the testing site needs to be clean.

Meter Hygiene: Follow the directions for making sure the meter is cleaned and maintained properly.

Alternative Site Testing: Not all areas of the body have the best blood for testing. The fingertip is one of the best and other areas will do. However, different areas can deliver different results.

Control Solution: Make sure you use the correct control solution and use it properly.

Temperature: There is often confusion over temperature. The meter and test strips often have DIFFERENT storage temperature ranges. AND, they can have DIFFERENT operating temperature ranges. Make sure you match these up or it can skew results. Often, you have to let both the meter and the strips adjust to the room temperature.

Expired Test Strips: Sometimes those bargain priced test strips aren’t such a bargain. Make sure the strips are not expired.

Wrong Test Strips: Most meters have proprietary test strips. Make sure you buy and use the correct ones.

Improper Testing Procedure: This is a bit of a catch all category. Possible errors include: Too much (or not enough) blood on the test strip and too much pressure on the test strip (often caused by smearing the blood on the strip).

Humidity and Altitude: Extreme humidity or altitude can affect testing accuracy.

Blood Quality: Sometimes the quality of the blood can affect your blood glucose meter accuracy. For example, certain medical conditions, treatments, medications and other substances can cause errors.

Hematocrit: Hematocrit is the level of red blood cells in your blood. Some people have higher levels than others. A high red blood cell count can adversely affect the reading.

Meter Quality: Often, there is a reason that meter was free or only $4. Sometimes, you get what you pay for.

Whole versus Plasma Blood Testing: Why don’t your lab results mirror your glucose meter results? Glucose Meters test your sugar levels using whole blood. Laboratory glucose testing uses blood plasma. Whole blood results are typically 10-15 percent LOWER than lab results. Next time you have lab work done, read your meter manual and speak with your doctor about how to best coordinate the readings, so you can see how far off your meter is from the lab results.

One last note: Different meters perform differently, as detailed more below. Thus, if you try and test alternatively with two different meters you are bound to get different results. Stick with one meter and you should get more consistent results.


meter accuracyAll glucose meters sold in the United States must pass a battery of tests implemented by the Food and Drug Administration (FDA). One of the tests conducted is for the blood glucose meter accuracy. The FDA utilizes testing standards derived by the ISO or International Organization for Standardization. Don’t ask me why the abbreviation doesn’t match the name, i.e., it should be IOS, not ISO.

Anyway, the standard at issue is ISO/DIS 15197

In vitro diagnostic test systems — Requirements for blood-glucose monitoring systems for self-testing in managing diabetes mellitus

To completely over simplify the standard, ISO/DIS 15197 requires the following:

Blood Samples less than 75m/dL – 95 percent of results must be within +/- 15mg/dL (of control)

Blood Samples more than or equal to 75 mg/dL – 95 percent of results must be within +/- 20 percent (of control)

Thus, if the reference sample was 74 mg/dL, the meter passes if it returns a result between 59 mg/dL and 89 mg/dL.

New standards are currently under evaluation, but you get the idea. There is a fair amount of allowed error. This is the key reason why many people see such a huge range of results.


So, is it even worth testing? I would say yes. BUT, you need to pick a good meter and stick with it. Also, follow all of the directions that come with the meter. If you buy the fanciest glucose meter but don’t know how to use it, then what was the point? Hopefully, this explains your blood glucose meter accuracy questions.

Good Luck Testing!


FDA Meter Accuracy Standards, (accessed May 2013).
By Erich Schultz – Last Reviewed May 2013.