If you use a glucose meter to manage diabetes, you may have wondered, “How do I know if my glucose meter is accurate?” or “Can I trust my blood glucose meter readings?”

Glucose meters are important tools for diabetes care. They’re usually accurate, but readings can sometimes be off for several reasons. In this article, we’ll explain how glucose meters work, what can affect their accuracy, and how you can check or improve their reliability.

Understanding Glucose Meters

Glucose meters are small medical devices that help people with diabetes check their blood sugar (blood glucose). You may also hear them called blood glucose monitoring devices or finger-stick checks.

To use a glucose meter, you prick your fingertip to produce a small drop of blood. Then, you place that blood on a test strip. The test strip goes into the glucose meter, which shows your blood glucose levels on the screen.

If you have diabetes, it’s important to check your blood sugar levels throughout the day. These numbers can help you make decisions about what to eat, how much to exercise, and when to take medication. Since a glucose meter only shows blood sugar levels at a specific moment in time, you’ll usually need to check levels several times a day, such as in the morning and before and after eating.

If you’re unsure when or how often you should be checking your blood sugar levels, ask your doctor. Your target blood glucose range is personal to you. A reading that is good for you may not be the same for someone else.

How Accurate Are Glucose Meters Really?

Having an accurate glucose meter matters because people with diabetes use the data to make critical choices regarding insulin and food. Incorrect readings can lead to choices that harm your health. For example, if the meter shows a high reading when your blood sugar is actually normal or low, you might take insulin you don’t need, which can be dangerous. Also, some continuous glucose monitors (CGMs) require calibration using a glucose meter, which makes accuracy even more important.

Most glucose meters sold in the U.S. must operate within an accuracy threshold set by the U.S. Food and Drug Administration (FDA). FDA guidance for over-the-counter blood glucose meters says that, compared with lab testing, 95 percent of meter readings should be within ±15 percent, and 99 percent of meter readings should be within ±20 percent, across the meter’s stated measuring range.

Glucose meters used by healthcare providers in facilities have a higher standard, requiring 98 percent of readings to fall within 12 percent of laboratory results. Clearance relies on specified performance criteria that are evaluated against laboratory-measured results obtained under certain conditions.

Even with FDA approval, though, not all meters work the same. A 2018 study looked at 18 popular glucose meters and found that only six of them met accuracy standards in every test. The study also found that four of the glucose meters didn’t meet accuracy standards in any of the tests. This means that while most meters are generally reliable, some may give inaccurate readings more often.

Newer Meters Versus Older Meters

Newer glucose meters are usually more accurate than older ones and often have helpful features. However, a higher price doesn’t always mean better accuracy. Some affordable meters perform just as well as more expensive ones.

When choosing a meter, it’s important to think about what works best for you. You may prefer a glucose meter that is easy to use, gives fast results, or is covered by your insurance plan. If you’re unsure which meter best fits your needs, ask your doctor. You can also check blood glucose monitor product reviews and comparison guides online.

Other Blood Glucose Tests

Continuous glucose monitors (CGMs) are another way to monitor blood sugar. A CGM uses a small sensor under the skin to measure glucose in the fluid around your cells. It provides readings every few minutes and can alert you when your blood sugar is too high or too low.

Since CGMs measure glucose differently from traditional meters, their accuracy can vary depending on the brand and situation. Many CGMs today are factory calibrated and don’t require routine finger-stick calibration, though finger-stick checks may still be recommended in certain situations — for example, if symptoms don’t match readings or if your glucose levels are changing rapidly. Some systems allow optional calibration.

Even if you use a CGM, you may still check your blood sugar levels with a traditional glucose meter from time to time. Your doctor may also have to order an A1c blood test. This test measures your average blood sugar levels over the past three months and helps show how well your current diabetes treatment plan is working.

Factors That Affect Glucose Meter Accuracy

Even the most accurate glucose monitors can give inaccurate readings if certain conditions aren’t right. The following factors can cause false blood sugar readings.

Not Preparing Properly

If you don’t wash your hands before testing, substances like sugar, lotion, or dirt on your skin can affect the reading. Wash your hands with soap and water, then dry them completely. Hand sanitizer alone isn’t enough.

User Error

You need enough blood on the test strip for your meter to work. If your hands are cold, it can be hard for enough blood to flow into your fingertips for a sample. Try warming your hands under warm water or by rubbing them together before washing.

If the first drop of blood is too small, don’t add more blood to the same strip. Instead, use a new test strip.

Keep in mind that using test sites other than your fingertips may give less accurate results.

Issues With Test Strips

Test strips can become inaccurate if they’re expired or exposed to heat, moisture, or air. Store them in their original container per the instruction manual, and be sure the lid is closed tightly. Check the expiration date, and make sure your test strips are compatible with your specific glucose meter.

Meter Calibration

Some glucose meters need to be calibrated to ensure accurate readings. If the calibration is off, readings may be inaccurate. This may involve using a control solution or a special calibration strip, depending on the meter. The control solution is a liquid with a known glucose range applied to a test strip to verify the meter is working.

Some meters perform automatic checks when turned on. If the meter detects a problem, it may show an error code. Refer to your instruction manual to understand what the code means.

Environmental Conditions

Extreme temperatures, either hot or cold, can affect both the meter and the strips. Humidity and high altitude can also create inaccurate results.

Certain Health Concerns

If you’re dehydrated or have low red blood cell counts (anemia), your readings may be inaccurate. High levels of red blood cells (hematocrit) or uric acid in the body can also affect your blood glucose and generate less accurate results.

Some Medications

Some medications and supplements can interfere with glucose meter readings. Talk to your doctor about potential interference from any medications or supplements you’re taking. Don’t change any medications without discussing it with a healthcare provider first.

Tips To Improve Your Meter’s Reliability

To get the most accurate results from your glucose meter, follow these tips:

• Take care of your meter, and replace batteries or recharge it when needed.
• Wash and dry your hands before checking your blood sugar.
• Use fresh test strips and store them correctly. Make sure the test strips are compatible with your specific glucose meter.
• Try to keep your test strips and meter at room temperature. If you need to test in very hot or cold environments, check your meter’s instruction manual for guidance.
• Use control solutions or built-in electronic checks to see if your meter is working correctly — especially when you open a new box of test strips or if the meter has been dropped.
• Compare your meter’s reading with a lab test from time to time. Bring your meter to your doctor’s appointment and test at the same time your blood is drawn — your doctor can also watch your technique and suggest improvements if needed.

When To Doubt a Reading — and What To Do

Sometimes, a reading just doesn’t seem right. You might feel fine, but your meter shows a sudden spike or drop. Or maybe you test again and get a very different result. You may want to question a reading when it doesn’t match how you feel, the number is very different from your usual range, or a repeat test gives you a very different number.

In these situations, try the following:

• Wash your hands and test again.
• Use a different finger or alternate site.
• Use a control solution to check your meter.
• Compare with a lab test if the issue continues.

If you’re still unsure, call your doctor or seek emergency help right away. A healthcare professional may retest you using a more accurate device.

Accuracy Matters

So, how reliable are glucose monitors? In general, they’re reliable tools — but they’re not perfect. Even a high-quality meter can give an inaccurate reading if it’s used incorrectly or stored in poor conditions.

By choosing a trusted meter, using it correctly, and checking it against lab results every now and then, you can feel more confident in your readings. And remember — when in doubt, retest and talk to your doctor.

Join the Conversation

On DiabetesTeam, people share their experiences with diabetes, get advice, and find support from others who understand.

Do you take steps to get the most accurate readings from your glucose meter? Let others know in the comments below.