Why Blood Sugar Readings Can Be Inaccurate

Why Your Blood Sugar Meter May Not Be Telling the Whole Truth

You prick your finger, wait a few seconds, and trust that number on your screen with major health decisions — adjusting insulin doses, deciding what to eat, or knowing whether it's safe to drive. But what if that reading is wrong? Inaccurate blood glucose results are more common than most people realize, and understanding the causes can literally be lifesaving.

Common Causes of Inaccurate Blood Sugar Readings

1. Expired or Improperly Stored Test Strips

Test strips are the most frequent culprit behind inaccurate readings. Each strip contains glucose-sensitive enzymes that degrade over time or when exposed to heat, humidity, or air. Always check the expiration date before testing, and never store strips in a bathroom medicine cabinet or car glove compartment. At mdsdiabetes.com, you'll find fresh, properly stored test strips from trusted brands to help ensure accuracy every time.

2. Residue on Your Hands

Fruit juice, sugar, lotion, or even hand sanitizer residue on your fingertips can dramatically skew results — sometimes by 100 mg/dL or more. Always wash your hands thoroughly with soap and warm water and dry them completely before testing. Alcohol wipes can help in a pinch, but make sure the site is fully dry before lancing.

3. Inadequate Blood Sample Size

Using too small a blood drop can cause your meter to under-read glucose levels. Most modern meters require a very small sample, but if you're struggling to get enough blood, try warming your hands first or using a fresh lancet. Dull lancets make it harder to produce an adequate sample and increase discomfort.

4. Meter Coding Errors

Older meter models require manual coding to match the strip lot number. Forgetting this step — or entering the wrong code — can cause consistent errors across all readings. Many newer meters auto-code, which eliminates this problem entirely.

5. Hematocrit Levels

Your hematocrit (the percentage of red blood cells in your blood) can affect meter accuracy. Conditions like anemia or dehydration alter hematocrit levels and may cause your meter to read falsely high or low. If you have such conditions, talk to your doctor about meters specifically designed to compensate for hematocrit variation.

6. Temperature and Altitude

Most meters are calibrated to work in temperatures between 50°F and 104°F. Testing in a very cold or hot environment can produce unreliable results. High altitude can also affect some meters' accuracy.

7. Meter Calibration and Quality

Not all blood glucose meters are created equal. Lower-quality meters may have wider acceptable error margins. Look for meters that meet ISO 15197:2013 standards, which require 95% of readings to fall within 15 mg/dL (for readings below 100) or within 15% of the true value.

How to Verify Your Meter's Accuracy

• Use the control solution that comes with your meter to run a quality check
• Bring your meter to a lab test appointment and compare results
• Replace your meter if it consistently reads differently from lab values by more than 15%
• Keep a testing log to spot patterns in unusual readings

Choosing Reliable Supplies

Accuracy starts with quality supplies. MDS Diabetes at mdsdiabetes.com carries a curated selection of blood glucose meters, compatible test strips, and lancets designed for consistent, reliable results. Whether you use a brand-name meter or a value-friendly option, pairing it with genuine, unexpired supplies is the foundation of trustworthy glucose monitoring.

When to Be Extra Cautious

Always be especially skeptical of readings that don't match how you physically feel. If your meter shows 60 mg/dL but you have no hypoglycemia symptoms, or reads 250 mg/dL but you feel completely normal, retest with a fresh strip. When in doubt, a second reading is always worth the extra strip.