Tracking blood glucose levels is an important part of managing diabetes, no matter what type you have. However, sometimes you might get a falsely high blood glucose reading that doesn’t match how you’re feeling. There are plenty of things besides diabetes that can cause false high blood sugar readings. Many of these factors are unrelated to your actual blood glucose levels. Below are 10 possible reasons for a false reading, along with tips to ensure your results are accurate.

1. Residue on Your Hands

One of the most common causes of a false high blood glucose test is residue left on your fingers. If you’ve recently eaten or touched anything with sugar (like fruit, drinks, or even lotions), it can affect your blood sugar reading. Even a small amount of sugar left on your hands can mix with your blood when you prick your finger for a blood sample. This can skew the results, leading to a false high reading.

To avoid this, always wash your hands with soap and water before testing. Be sure your hands are completely dry, as even water can dilute the blood and affect your results. If you can’t wash your hands, you can use an alcohol wipe, but make sure your finger is dry before you test. Cleaning your hands properly will give you a more accurate reading.

2. Contaminated or Expired Test Strips

Test strips are key to getting an accurate blood glucose reading. If your test strips are expired or contaminated, they can give you false results. Test strips are sensitive to light, temperature, and humidity, so storing them improperly can lead to inaccurate readings.

It’s important to store your test strips in a cool, dry place, away from direct sunlight and moisture, to make sure they are accurate. Additionally, always check the expiration date on the test strip vial before using them. Expired strips may not work correctly and can lead to a false high blood sugar reading. Always use a new strip for each test, and avoid touching the part of the strip that comes into contact with your blood.

3. Extreme Temperatures

Both your blood glucose meter and your test strips are sensitive to extreme temperatures. Whether it’s too hot or too cold, temperature extremes can cause your equipment to malfunction, giving you false high blood sugar readings. For example, leaving your meter or test strips in the car on a hot day or storing them in a cold place can lead to errors.

To prevent this, always store your testing supplies at room temperature. Keep them away from direct sunlight, freezing temperatures, and excessive heat. If you think your equipment has been exposed to extreme conditions, recheck your blood glucose levels with a different set of test strips or a different meter to confirm your results.

4. A Low Battery

A low battery in your blood glucose meter can also cause false high blood sugar readings. When the battery is running low, the meter may not work properly, giving inaccurate results on your blood sugar test.

To get accurate readings, it’s essential to check your meter’s battery regularly and replace the monitor every four to five years. Some meters have indicators that warn you when the battery is low. Keeping extra batteries on hand ensures you’re always prepared.

5. Testing Two Different Blood Sugar Readings Within Seconds

Have you ever tested your blood glucose levels twice in a row and gotten different results? This happens more often than you might think. While it’s generally not a cause for concern, it can happen for a few reasons. Differences in the size of the drop of blood or which fingertip you use can lead to slightly different readings.

For instance, when using a small blood sample, the glucose concentration might not be fully accurate, causing slight differences between tests. To minimize these differences, use the same fingertip and make sure you have enough blood for each sample. Always follow your blood glucose meter’s instructions to ensure more consistent test results.

6. Stress or Illness

Stress, both physical and emotional, can cause your blood glucose levels to rise unexpectedly. When you're stressed, your body releases hormones like cortisol and adrenaline, which can cause high blood sugar levels. Illness or infection can have a similar effect, as your immune system kicks into gear, raising glucose levels in the process.

If you’re feeling stressed or sick and notice higher readings than usual, this could be the cause. It’s important to keep monitoring your blood glucose levels during these times and consult your doctor if the readings stay high for a long time. Understanding how stress and illness can affect your blood sugar can help you stay on top of your diabetes management.

7. Vitamin C Interference

High doses of vitamin C can affect certain blood glucose meters, leading to false high blood sugar readings. Some meters — not all — mistake vitamin C for glucose in the blood sample, causing inaccurate readings.

If you take vitamin C supplements or are on a high-dose vitamin C regimen, talk to your doctor about how this might impact your readings. Your health care provider can help you find a meter that isn’t affected by vitamin C or suggest changes to your testing routine.

8. Squeezing Your Finger for a Blood Sample

Squeezing your finger too hard to get a drop of blood can mix the blood with fluids from surrounding tissues. This can lead to a false high blood sugar reading. This tends to happen especially if you’re struggling to get enough blood for the fingerstick.

Instead, let your blood flow naturally. If needed, try warming your hands under warm water or gently massaging your finger before pricking it to get your blood sample. This can help improve blood flow and give you a better sample.

9. Certain Medications

Some medications can cause your blood glucose levels to rise, even if you keep a consistent diet and exercise routine. For example, steroids (like those prescribed for inflammation) and beta-blockers (commonly used for heart disease) can raise blood sugar. Some antipsychotics and certain types of immunosuppressants are also known to raise blood glucose. These medications can affect how your body produces or uses insulin, leading to high blood sugar readings.

If you’ve started a new medication and notice unusual fluctuations in your blood glucose levels, talk to your doctor. You may need to adjust your diabetes care plan.

10. Recent Eating or Drinking

What and when you eat plays a significant role in your blood glucose levels. Testing too soon after a meal, especially one high in carbohydrates, can lead to falsely high blood sugar readings. This is because carbohydrates are broken down into glucose quickly, which raises your blood glucose shortly after eating.

It’s best to test one to two hours after eating, as recommended by the American Diabetes Association. This gives your body time to process the food, giving a more accurate picture of how your body is managing glucose.

Why Is Your Blood Sugar Reading Different in Each Hand?

If you’ve noticed that your blood glucose monitoring changes depending on which hand you use, don’t worry — this is normal. The difference is usually due to blood flow. One hand, especially your dominant one, may have better circulation than the other, leading to a slightly different blood sugar reading.

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