Blood glucose meters are extremely valuable tools if you have diabetes, follow the ketogenic diet, or simply want to improve your metabolic health.
While at-home meters aren’t as accurate as “gold standard” lab tests, they’re still accurate enough to ensure you make safe decisions about glucose management–and they’re also strictly regulated by the FDA and other governing bodies as medical devices. If you’re feeling doubtful about the accuracy of your meter, this guide has the facts to help put your mind at ease. But just as importantly, you’ll also learn how to check your meter for accuracy using a control solution if necessary, as well as the most common factors that can cause inaccurate readings (and how to prevent that from happening). Keep reading to learn the truth about meter accuracy, how accuracy is defined, how at-home meters compare to lab tests, how to test accuracy, and more.
5 Facts to Know About Glucometer Meter Accuracy
[1] Accuracy Is a Technical Term Defined and Regulated by the FDA
In the United States and most other countries (including those in the European Union), over-the-counter glucose meters are regulated as medical devices and have to meet strict requirements before going to market.
Under FDA regulations, all blood glucose meters must meet or exceed the following accuracy standards to meet a 510k certification:
- 99% of all results must be within +/- 20% of a validated laboratory-based glucose measuring method
- 95% of all results must be within +/- 15% of a validated laboratory-based glucose measuring method
As an example, if the laboratory reference test for blood glucose showed a result of 100 milligrams per deciliter (mg/dL), then a self-monitoring glucose meter would need to show 99% of results between 80-120 mg/dL and 95% of results between 85-115 mg/dL for the same sample.
The FDA also requires manufacturers to demonstrate precision (repeatability of results) for different glucose concentrations between 30-400 mg/dL to help ensure the meter performs adequately across the entire spectrum of possible results (from dangerously low, to normal, to dangerously high).
Along with testing meters, manufacturers also have to show their glucose strips are accurate, and must test strips from all batches and also keep an archive of strips in case a problem comes to light into the future.
In other words, by the time you purchase a glucometer and strips, the manufacturer has done everything possible to guarantee their products are safe and effective for the purpose of monitoring your blood glucose and using the results to make decisions.
On the other hand, stand-alone blood glucose meters are not strictly regulated in the same way as glucometers, but combination glucose meters must meet higher standards than glucose meters.
Therefore, if you want the most accurate blood glucose readings possible, be sure to choose a 510k approved FDA-compliant glucose meter rather than a non-regulated meter that only reads glucose levels. Generally, glucose only meters do not need to meet the same stringent 510k FDA standards for glucometers so using a glucose meter ensures greater levels of assurance.
[2] No Meter Is as Accurate as a Lab Test or Venous Blood Draw
Keep in mind that the strict regulations for glucose meters (and strips) ensure they’re accurate enough to help you make the correct decisions, safely and consistently, based on your blood glucose levels.
That said, no self-monitoring blood glucose test system is as accurate as a lab test, for several reasons.
First of all, glucose meters use very small samples of your blood that come from a fingerstick blood droplet. This blood is called capillary blood because it comes from your capillaries.
Your capillaries are responsible for delivering blood directly to the tissues in your body, and your metabolism can more readily affect the glucose content of capillary blood compared to other sources.
Unlike home glucometers, medical lab tests use venous blood drawn directly from a vein. Venous blood is more representative of your body’s circulating glucose levels and is typically lower than glucose levels from capillary blood.
The sample size also makes a significant difference in accuracy and precision. A glucose strip reservoir is typically less than one microliter, or under one thousandth of a milliliter.
In contrast, lab tests analyze blood samples around 0.5 milliliters, 500 times larger than the capacity of a glucose strip reservoir.
And as with any measurement, a larger sample size yields more reliable results. The contents of your blood (including blood sugar) are not 100% uniform, but are distributed somewhat unevenly, meaning that a smaller sample is more likely to show a difference from your average levels compared to a larger sample.
Finally, there’s a huge difference between home equipment and lab equipment.
Glucose meters cost approximately as much as an oil change for your car (and report results in 5 seconds), while the “gold standard” test, gas chromatography-mass spectrometry (GCMS), uses instruments that cost between $80,000-$400,000 (and takes at least 15 minutes to report results).
The next step down in lab equipment used to measure glucose, like the YSI bench analyzer used in FDA 510k submissions, costs approximately $25,000.
GCMS tests or bench analyzers also require a phlebotomist or nurse to draw your blood, as well as a lab technician to process the blood sample and interpret the results.
[3] High Quality Consumer Glucose Meters Are Accurate Enough
It would be wonderful if consumer-grade glucose meters could rival the accuracy of lab-grade GCMS equipment.
In reality, though, they’re still accurate enough for their intended purposes.
The most important role of a glucose meter is risk management by assisting acute care decisions around blood sugar, such as detecting dangerously low or dangerously high levels that require immediate attention. It’s also used in assessing ongoing needs for exogenous insulin to maintain healthy blood glucose levels.
And by virtue of meeting the FDA risk management standards for making critical decisions, home glucose meters are also accurate enough for:
- Tracking trends in glucose over time (for example, fasting morning glucose) to measure your metabolic health,
- Understanding your response to a meal or specific food by testing pre and postprandial glucose for people with diabetes or who are on the ketogenic diet.
And finally, unlike lab instruments that occupy an area the size of a large closet and require specially trained personnel to operate, glucometers are portable and easy to use–you can keep them nearby and use them in situations where a lab test would never work.
[4] Comparing Results from Different Brands of Meters
If you own more than one type of meter, or have friends or family members who own their own glucometers, you may be tempted to compare results from different brands of meters.
Unfortunately, this practice is not a reliable way to compare accuracy.
It’s not widely discussed, but at Glucoracy®, we’ve discovered through internal testing that some brands of glucose meters provide lower results than lab results in general, even if the results are still technically within the FDA’s acceptable accuracy range. That is, they skew measurably and consistently towards the very bottom of that range.
You can view the actual data by reading down to the bottom of this article.
While meters with a tendency to read low are still considered accurate enough for making appropriate care decisions (since they meet the accuracy standards), they sometimes cause problems, such as:
- when people switch from a meter that skews low to one that doesn’t, they may worry that their glucose management strategies aren’t effective, or
- sometimes people switch from or compare meters, then assume the higher reading of the two must be inaccurate or defective.
It’s generally true that people prefer low readings to high ones for a lot of reasons, especially because lower readings suggest effective blood glucose management and good metabolic health. The tendency to accept data or results that fit our preferences is known as confirmation bias, and no one is completely immune to this form of bias.
However, just because one meter consistently reads lower than another doesn’t make it more accurate, valid, or useful than another meter. On average, the meter that doesn’t skew low may actually be more likely to give an accurate reading.
Overall, what matters the most is staying with one trustworthy meter, making the right short-term glucose management decisions, and monitoring your metabolic health trends over time.
[5] Comparing Back-to-Back Results
Intuitively, it may seem that comparing back-to-back results from the same glucose or glucose meter would be a helpful way to determine its accuracy or to receive more accurate readings, but that’s actually not the case.
(If you want to know the best way to validate the accuracy of your glucose meter, that’s covered in the section directly below this one.)
First, as we’ve discussed previously in this article, keep in mind that expected variations in readings will occur:
- +/- 15% variation compared to baseline lab results, 95% of the time
- +/- 20% variation compared to baseline lab results, 99% of the time
Therefore, for example, a repeat reading of a lab-validated glucose sample that’s 100 mg/dL would be expected to range from 85-115 mg/dL with a home glucometer.
Beyond that, performing back-to-back readings at home further decreases accuracy for these reasons:
- If you use a single sample (blood droplet), prolonged exposure to air skews readings because glucose oxidizes (reacts to oxygen).
- Blood glucose levels can change rapidly in your body, so even samples taken close to one another in time can be different.
- Taking readings using samples from different fingers may result in differences because the glucose content of fluids from different body areas can be different.
In other words, just because back-to-back readings may differ, it doesn’t mean your meter is inaccurate.
If you’re concerned about the accuracy of your glucose meter, keep reading for tips on how to conduct an accuracy test and learn about other factors that could affect accuracy.
