The short answer
Glucose meter accuracy standards describe how closely a meter's reading is expected to match a laboratory reference value. The most widely referenced standard for consumer blood glucose meters is ISO 15197, which sets accuracy expectations for systems used in self-monitoring. In practical terms, a meter that meets the standard can still give a reading that differs from your true blood glucose level by a noticeable amount, especially at higher glucose values. That is why a single reading is best understood as an estimate, not an exact value, and why trends over time are often more useful than any one number.
FDA also notes that the safe use and accuracy of a blood glucose monitoring device depends on many factors beyond the meter itself, including the quality of the meter and test strips, how well you perform the test, certain health conditions, medications and supplements, and the environment where you test. This article explains those factors in general terms. It cannot tell you whether a specific reading is correct for you.[source]
Different readings? Use this short checklist
If two readings seem inconsistent, start with how you feel and with your established diabetes care plan. Do not delay urgent medical help while you keep troubleshooting readings. If you have symptoms of low or high blood sugar, or a reading does not match how you feel, follow the plan you and your healthcare professional have already agreed on and contact them as that plan directs.[source]
Next, check the basics. Wash and dry your hands before testing, and use only the test strips specified for your meter. A strip that fits the slot is not proof of compatibility: FDA notes that using a test strip not recommended for a meter may cause the device to fail to give results or to generate inaccurate results, and advises reading the owner's manual and using only the strips specified for that meter. Check expiry and storage too, since improperly stored meters and test strips may make results less accurate.[source][source]
Then follow your meter's own instructions for the sample, for any error message, and for any appropriate repeat test; there is no universal number of repeats or cross-model procedure. A control-solution check, used according to its instructions, assesses the meter-and-strip system; it does not measure your blood glucose or prescribe treatment. Note the time, readings, symptoms and relevant circumstances so your care team can review your technique or the manufacturer can offer support. Two home meters are not a laboratory reference.[source]
What the evidence supports
Accuracy standards such as ISO 15197 are written for manufacturers and regulators, but they translate into a few patient-relevant facts. First, accuracy is defined against a laboratory reference method, not against another meter. Two meters can both meet the standard and still disagree with each other because each has its own allowable error. Second, the standard applies to the meter system as a whole, including the test strips and the user's technique. A meter that performed well in a laboratory study may not perform the same way in everyday use if strips are stored incorrectly or if the blood sample is too small. Third, the standard sets minimum performance expectations, not a guarantee for every single reading. A meter that meets ISO 15197 can still produce an occasional outlier result. For patients, the practical takeaway is that accuracy information in the instructions or labeling describes expected performance across many readings, not a promise about any one reading.
FDA's guidance on self-monitoring blood glucose test systems for over-the-counter use is aimed at manufacturers preparing premarket submissions. It describes the performance studies FDA recommends for these devices and notes that the guidance does not address blood glucose monitoring test systems intended for prescription point-of-care use in professional healthcare settings, which FDA covers in a separate guidance. For patients, the practical point is that the accuracy information in your meter's labeling reflects a regulatory review process designed for home-use devices, and that home-use and professional-use systems are evaluated under different frameworks.[source]
FDA also describes how a blood glucose test system works and how patients can check that it is operating normally. A test system includes a handheld meter and test strips, and the strip contains chemicals that react with glucose, with the meter measuring that reaction using electricity or light. FDA lists three ways to check meter performance: control solutions, the electronic check the meter performs when turned on, and comparing your meter with a laboratory blood test, for example by bringing your meter to an appointment and asking your healthcare provider to observe your technique.[source]
Practical considerations
Several everyday factors can affect how closely your meter reading matches your true blood glucose. FDA notes that accuracy depends on the quality of your meter and test strips, including using new test strips authorized for sale in the United States, and on how well you perform the test, such as washing and drying your hands and closely following the instructions for operating your meter. Storage and handling matter too: improperly stored meters and test strips may cause results to be less accurate, and if your strips come in a vial, the vial should be tightly closed when not in use. High altitude, extreme temperature, and extreme humidity may also have unpredictable effects on results, so check the operating conditions in your meter manual and test strip instructions.[source]
Some health conditions and substances can influence results. FDA notes that severe dehydration or anemia, an extreme hematocrit (the amount of red blood cells in the blood), and conditions associated with high uric acid such as gout may affect your glucose result. Certain medications and supplements may also interfere with the test; FDA gives vitamin C, acetaminophen and acetaminophen-containing drugs such as Tylenol, and Xylose absorption therapies as examples. Check the instructions for your meter and test strips to find out what substances may affect the result, and ask your healthcare provider if you take medications or supplements that may interfere.[source]
Alternative site testing, which uses blood from places such as the palm, upper arm, forearm, thigh, or calf instead of the fingertip, may be less accurate when glucose is changing rapidly. FDA advises testing from your fingertip if you are ill, have just eaten, are under stress, have just exercised, have just taken insulin, think your blood sugar is low, find that results do not agree with how you feel, or are not aware of symptoms when you are hypoglycemic. FDA also states that results from an alternative sampling site should never be used to calibrate a continuous glucose monitor or for insulin dosing calculations.[source]
When you want to understand your own meter's accuracy, the most reliable source is the documentation that came with the device. Look for the accuracy section in the user manual or the test strip insert. It should state the standard the system meets, such as ISO 15197, and may include a table showing how often results fell within specific ranges. If the information is not clear, ask the manufacturer or your pharmacist for the accuracy specification. The table below lists questions you can use to check whether the information you find is complete enough to be useful, and you can also bring these questions to your healthcare professional.
| Question | Why it matters |
|---|---|
| Which accuracy standard does the system meet? | Different standards use different criteria, so the standard name tells you what was measured. |
| What reference method was used for comparison? | Accuracy is always relative to a reference, and the reference affects the result. |
| Does the accuracy claim apply to the meter alone or the full system with strips? | Strips and technique are part of the system, so a meter-only claim may not reflect everyday use. |
| Are there conditions where accuracy may be reduced? | FDA notes that health conditions, medications, and environmental conditions can affect results. |
| How can I check that my meter is working properly? | FDA describes control solutions, electronic checks, and comparison with a laboratory test. |
| How can I report a reading that seems wrong? | The manufacturer can explain whether the result is within expected variation or needs investigation. |
Limits and responsible use
This article is general education, not medical advice. It cannot tell you whether your meter is accurate enough for your treatment decisions, and it cannot replace the instructions from your healthcare professional. Accuracy standards describe expected performance across a population of readings; they do not guarantee that any single reading is correct. If you use a continuous glucose monitor or another device, its accuracy characteristics may be different, and you should follow the labeling for that device. For questions about your diabetes management, including how to interpret a reading that seems unusual, contact your healthcare professional. For more context on related topics, you can read about the cost of meters and test strips and insurance coverage basics, or about over-the-counter CGM benefits and limitations.
Frequently Asked Questions
What does it mean if my glucose meter meets ISO 15197?
It means the meter system is expected to perform within the accuracy criteria defined in that standard, measured against a laboratory reference method. It describes expected performance across many readings and does not guarantee that any single reading is exact.
Is FDA guidance the same as an accuracy standard like ISO 15197?
No. FDA guidance describes the studies and information FDA recommends manufacturers submit when seeking clearance for over-the-counter self-monitoring blood glucose test systems. ISO 15197 is a performance standard that defines accuracy criteria. They serve different purposes, and the numeric thresholds should be confirmed from the standard or your meter's labeling.
Why can two meters that both meet the standard give different readings?
Each meter system has its own allowable error, and accuracy is defined against a laboratory reference rather than against another meter. Two systems can both meet the standard and still disagree with each other.
What can make my reading less accurate?
FDA notes that accuracy depends on the quality of the meter and test strips, how well you perform the test, certain health conditions such as severe dehydration or anemia, medications and supplements that may interfere, and environmental conditions such as extreme temperature or humidity.
How can I check that my meter is working properly?
FDA describes three approaches: control solution tests, the electronic check the meter performs when turned on, and comparing your meter with a laboratory blood test, for example by bringing your meter to an appointment and asking your healthcare provider to observe your technique.
Can I use blood from somewhere other than my fingertip?
Some meters offer alternative site testing, but FDA notes it may be less accurate when glucose is changing rapidly and advises fingertip testing in several situations, such as when you are ill or think your blood sugar is low. FDA also states that alternative site results should never be used to calibrate a continuous glucose monitor or for insulin dosing calculations.
What should I do if two readings seem inconsistent?
Start with how you feel and your established diabetes care plan, and do not delay urgent medical help while troubleshooting. Then check washed and dried hands, that your strips are the ones specified for your meter, and expiry and storage. Follow your meter's own instructions for samples, error messages and any repeat test, and note time, readings, symptoms and circumstances for a care-team technique review or manufacturer support.