Diabetics can use glucose meters to take care of their health

Are Blood Glucose Monitors Accurate?

It is not uncommon for patients with diabetes to have issues with monitoring their blood sugar levels at home due to the incorrect readings shown by their blood glucose monitors. Read more here on how to measure your blood glucose levels.

They often have concerns regarding whether their blood glucose monitor is working properly and showing the correct reading.

If you are worried about your blood glucose monitor not showing accurate results, keep reading. We will discuss the best ways to find whether a blood glucose monitor is working properly and how to identify and correct the issues that can cause inaccurate readings.

How do you use Glucometers?

When used correctly, most blood glucose monitors, also called glucometers – the small devices that can measure and display the blood sugar level – show accurate readings. You can even read your glucose levels with your tears!
However, they may show incorrect results occasionally.

Since your blood glucose readings determine the doses of insulin or other antidiabetic drugs you need to take and your dietary intake, it is important to ensure your glucometer is working perfectly.

Here are some factors that can affect the accuracy of your glucometer and the steps to prevent or resolve the issue:

How is Blood Glucose Accuracy Determined?

One of the best ways to determine the accuracy of your blood glucose reading is to use more than one method to check your levels and compare the results.

There are 2 basic methods to check your blood sugar levels as given below: 

  • Laboratory tests that are performed by healthcare professionals
  • At-home tests that you can perform using your personal blood glucose meter

Since the blood sugar levels tend to fluctuate on different days and even at different times on the same day, it is advisable to check your blood sugar levels using 2 methods at the same time.

Comparing the results will give you an idea of the accuracy of your device.

If both the results are similar without much variation, you can assume the glucometer you are using is working perfectly.

It is advisable to check the accuracy of your blood glucose meter at frequent intervals. Having a glucometer that provides correct results will allow you to monitor your blood sugar levels at home. It will ensure you are able to modify your dietary intake and medications in the most appropriate manner for improving your diabetic control. 

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How Are Blood Glucose Monitor Test Different?

Your personal glucometer can help you measure your blood glucose level using a small sample of blood from your fingertip (or any alternate site).

The test to check your blood sugar levels at home takes hardly a few minutes and provides an easy and convenient way to monitor your diabetes on a regular basis without having to travel to the laboratory.

The home test uses whole blood to measure the glucose levels.

Your blood sugar levels can also be measured in a laboratory by a healthcare professional. For this test, the sample of blood is typically drawn from a small vein in the arm and processed to separate the red blood cells, so that only the plasma can be tested.

There may be a minimal difference in the results of the tests performed at home or in a laboratory as both of these tests use different samples. While the at-home test uses whole blood to measure your blood sugar level, the test at a laboratory uses plasma.

Most glucose meters designed to be used at home factor in the difference caused due to the use of the whole blood sample while providing the test results so that they can be considered plasma equivalent.

The blood glucose meters do not always provide the exact measure of your blood glucose level. However, they are primarily designed to give you fairly accurate readings to help you make daily treatment decisions when you are not at the doctor’s office.

Laboratory testing generally demonstrates a higher level of accuracy compared to that of home testing using a personal glucometer. However, even the results with the laboratory tests may have a small margin of error.

There are several factors that can cause the readings by these 2 methods to vary slightly. Typically, the result from a personal meter can be considered accurate if it is within 15 to 20% of the laboratory reading.

For example, when your lab report shows that your blood sugar level is 100 mg/dL, and your glucometer at home shows the result in a range of 85 mg/dL to 115 mg/dL, it can still be considered accurate.

What Factors Can Affect the Accuracy of Blood Glucose Monitors?

Test Strips

The test strips help to measure the blood glucose levels based on the interaction of the glucose in your blood with certain enzymes on the strip.

The interaction between these enzymes and the glucose in your blood causes the release of electrons, which results in the creation of an electrical current. The glucometer then converts the electrical current into a specific concentration of glucose to give the reading.

Since this process is complicated, the test strips tend to be very sensitive to some variables.

Exposure of the test strips to certain factors can result in the failure of the enzymes to interact with blood glucose due to which you may get an inaccurate reading.

The inaccurate results may occur due to the faulty or improperly functioning test strips in the following cases:

  • Using expired test strips
  • Damage to test strips due to the exposure to heat and moisture
  • Not applying enough blood to the test part of the strip
  • Using strips that are not designed to be used with your glucometer
  • Have contaminants like lotion, oil, or food on the test area

These problems can be avoided by taking precautions such as storing them in a recommended manner.

You should always store the test strips in their container and the container should be stored at the temperature recommended by the manufacturer.

Also, make sure you are using strips that are specifically made for your glucometer model and have not expired.

The design of the test strips from different brands may vary. Hence, it is important to know the exact place where the blood sample is to be applied to avoid inaccurate results caused due to testing errors.

Environmental Conditions

The enzymes present in the test strips, and the flow and composition of your blood can get affected by certain conditions in the external environment.

For example; the active enzymes in the test strip chemistry are often sensitive to humidity and temperature conditions. The exposure of the strips to high temperature and humidity may reduce the activities of the enzymes thus affecting the accuracy of your blood glucose results.

Also, your body reacts to different temperatures in a different manner. The higher temperatures can cause your body to become dehydrated due to which the glucose level in your blood becomes concentrated. As a result, your reading may show an elevated level for the sample of blood used for the test.

Similarly, exposure to lower temperatures can affect blood circulation thus reducing the blood flow to the testing site. These factors can affect the accuracy of the results of home testing.

Studies have also revealed that the glucometers can both overestimate and underestimate the glucose levels when used at higher altitudes. Hence, it is advisable to confirm the altitude rating for the device you are using.

Substances on the skin

Substances that you had touched or put on your skin may end up contaminating your blood sample causing the results to show an error. 

Since most glucometers utilize a very small or micro-sized sample of blood, not washing your hands or touching anything that contains sugar could affect your reading.

Also, if you have washed your hands just before the testing and haven’t dried them completely, the water droplets left on your fingers may create a diluting effect on the blood sample causing errors in the reading.

You can avoid these errors by washing your hands and drying them thoroughly before every test.

Amount of blood sample used

Your blood glucose meter may show a wrong reading if the amount of blood used for the test is not enough or too much.

Most glucometers state the required sample size of blood. Usually, a very small sample of blood, around 0.5 microliters, is considered the ideal sample size for testing glucose levels.

How Can I Make Sure My Blood Glucose Monitor Provides Accurate Readings?

It is advisable to invest in a glucometer from a reputed brand that has been tested for its accuracy by an independent lab. It will also be helpful to compare the performances of the commercially available glucometers to find the one that provides results with a higher accuracy. 

What Factors Can Cause Inaccurate Blood Glucose Monitor Measurements?        

Several factors including the inaccurate use of test strips, external environmental conditions, and the use of a very small or large sample size can affect the accuracy of the blood glucose measurements.

We have already discussed these factors and how they affect the blood glucose reading. Let us have a glimpse of what you can do to avoid getting inaccurate results due to these factors.

Test Strip Problems

Check the expiry date of the test strip before using it. Avoid using damaged or expired test strips. Discard them in the recommended manner once the expiry date is over.

Store the strips in a sealed container and keep them away from humidity, heat, and moisture. Make sure you use the strips that are meant for your glucose meter.

Extreme Temperatures

To avoid getting inaccurate results due to the influence of the external environmental conditions, keep the test strips in a closed container at room temperature. Avoid leaving the container in a cold or hot car.

Take only one strip out whenever you want to test your glucose levels and close the container immediately.

If you are exposed to colder temperatures and if your hands feel too cold, hold them under warm water for a few seconds until they feel sufficiently warm before taking a test. This would improve the blood flow into your hands and decrease the chances of meter errors.

Other Substance On Your Skin

Dust, dirt, alcohol, or other substances can get on your skin and enter the sample of blood causing the glucometer to show inaccurate results. Always wash and dry your hands, especially, the testing site, thoroughly before the test.

Improper Coding of Devices

Some glucometers need to be coded to the container of the strips.

If your glucometer requires coding, it means you need to input the code printed on the test strip vial for calibrating it before use. In case the code does not match, it may lead to inaccurate readings.

You can also choose “No Code” glucometers to avoid this error. Using “No Code” glucometers can also let you avoid the step of matching the codes.

But, in case you are using the device that requires coding, make sure the code number on the container of your test strips matches the code number on your device.

Technical Monitor Problems

The enzymes, calibration process, and computer algorithms in every glucometer are different. The manufacturing and chemistry also differ among different brands and even across the product lines from the same brand.

If you are using a glucometer of a particular brand or a model, make sure you use the same to compare the results the next time.

If you use a different model each time, your readings may have significant variations due to which you might experience a difficulty in assessing the effects of medications. This can prevent you from modifying the treatment plan to improve glycemic control.

Hence, it is best to stick to using one glucose meter to make it easier to interpret the results and monitor the outcomes of your treatment decisions.

Also, following the instructions for using the glucometer and its proper maintenance are critical, irrespective of the brand you are using, to be able to get accurate readings.

Make sure you have inserted the test strip completely into the monitor. Also, replace the batteries in the monitor as and when needed.

Insufficient Amount of Blood Sample Used

It is important to touch a generous sample of blood to the test part of the strip. At the same time, you should not add more blood to the strip after applying the first drop.

You can experiment with different sizes of lancets to find the one that provides the best sample size you need. You should also avoid squeezing the finger directly around the test area when forming the blood drop.     

Testing Site Location

Physiological differences exist in the blood circulation through different parts of the body. Hence, the test results may vary depending on the site from which the blood sample is drawn.

Testing your blood glucose from alternate sites such as your forearms, thigh, or calf may provide less accurate results than testing with the sample from your fingertip.

The inaccurate results may occur due to the variations in the frequency with which blood circulates through these parts.

Also, if you have recently exercised, eaten, or taken any medication that might lower your glucose levels, the changes caused due to the same may not be reflected as quickly in the alternate sites as in the fingertip.

Moreover, blood samples from other sites may not show accurate results when your blood glucose level is fluctuating quickly.

Hence, it is best to use the sample of blood from your fingertip for checking your blood glucose levels. You can also check the instructions for your glucometer to learn how testing at alternate sites can affect the results.

If you are using a blood sample from a site other than the fingertip and you feel the reading might be wrong, you can test again using a sample from a fingertip.

Amount of Red Blood Cells

Variations in the hematocrit, which refers to the proportion of the RBCs (red blood cells) in the blood, may affect the accuracy of the reading provided by a blood glucose meter.

The variances in the counts of red cells may interfere with the calculation of blood glucose. For example; if you are dehydrated or if you are suffering from anemia that causes your red blood cell count to be low, the test results may not be accurate.

Luckily, some glucometers available today include the latest technologies that can help to correct the reading based on these hematocrit variations.

How to Ensure Your Blood Glucose Monitor Provides Accurate Readings    

Here are some quality control tests that can assure you that your blood glucose meter is working perfectly:

Test Using a Control Solution

You can perform the usual blood glucose testing procedure using a liquid control solution in place of blood to check the accuracy of your device. These solutions often come with the monitor and are also easily available at most pharmacies and drugstores.

Follow the package directions to use the liquid control solution each time you open a new container of strips. You can also use liquid control solutions to test your device in case you drop it, or when your think the results are unusual.

Match Your Reading With Lab Results

You may carry your personal blood glucose monitor with you while visiting a lab or your doctor for the test.

Check your blood glucose level using your meter at the same time a sample of blood is drawn for the lab test. Comparing the reading from your meter with the lab results will help you assess the accuracy of your device.

The results that are within 15 to 20% of the lab reading can be considered to be fairly accurate.

Know your risk of diabetic eye disease

Click here to download the RetinaRisk app now!


Blood glucose meters provide a convenient way to monitor your blood sugar levels at home as and when required.

It is important to ensure your blood glucose meter is providing accurate results. An improperly functioning device may show a wrong reading preventing you from making the right decisions for controlling diabetes.

Follow the methods discussed above to test your glucometer so that you are sure that your device is working perfectly and providing the correct readings.

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