How to Test Blood Sugar Correctly: Common Mistakes to Avoid

Blood sugar testing is something I do multiple times a day, and I’ve learned the hard way that doing it correctly matters! When I first got diagnosed with diabetes, I made so many mistakes with my glucose readings that my doctor was confused by the inconsistent numbers. In this guide, I’ll share everything I’ve learned about how to test blood sugar correctly, including the mistakes I made that you can avoid. Whether you’re newly diagnosed or have been testing for years, these tips might just change how you approach this daily ritual.

Why Accurate Blood Sugar Testing Matters

Testing your blood sugar correctly isn’t just about following doctor’s orders—it directly impacts how you manage your condition day-to-day. When I first started testing, I didn’t realize how much small errors could affect my readings and the decisions I made about food, medication, and activity.

Accurate readings help you:

• Make informed decisions about insulin dosing
• Understand how different foods affect your body
• Track patterns to prevent dangerous highs and lows
• Communicate effectively with your healthcare team
• Adjust your diabetes management plan as needed

I once spent three weeks adjusting my insulin based on faulty readings because I didn’t know I was making a basic testing mistake! Don’t put yourself through that frustration.

Common Blood Sugar Testing Mistakes to Avoid

Not Washing Your Hands Before Testing

This was my biggest mistake when I started testing my blood sugar! I can’t tell you how many times I’d quickly test after handling fruit or something sweet, only to panic at a seemingly high reading. Turns out, it was just residue on my fingers contaminating the sample!

Always wash your hands with warm water and soap before testing. If you’re away from home and can’t wash up, use an alcohol wipe and let it dry completely before pricking your finger. I learned that even hand lotion or sanitizer can affect your results, so a thorough hand-washing is really important.

One time at work, I tested after eating an apple without washing my hands and got a reading of 240 mg/dL. I nearly gave myself a correction dose of insulin before realizing my mistake! When I washed up and retested, my actual blood sugar was 135 mg/dL—quite a difference!

Using Incorrect Technique When Drawing Blood

Drawing blood seems straightforward, but there’s definitely a technique to it! For years, I squeezed my fingertip really hard to get enough blood, not realizing this was actually diluting my sample with tissue fluid and affecting my readings.

Instead of squeezing, try:

• Hanging your hand below your heart for a minute to increase blood flow
• Gently massaging your finger from base to tip
• Using the sides of your fingertips where there are fewer nerve endings
• Adjusting your lancing device to the appropriate depth (not too shallow, not too deep)

I also found that warming my hands under running water helps blood flow better, which is especially useful on cold mornings when getting a good sample seems impossible!

Not Using Enough Blood on the Test Strip

This mistake cost me a fortune in wasted test strips! Those things aren’t cheap, and I’d often get error messages because I didn’t apply enough blood to the strip. The meter would count down and then just display an error, forcing me to start over with a new strip.

Make sure you get a large enough drop of blood before applying it to the test strip. Most modern meters need just a tiny sample, but it still needs to fill the entire test area. Some meters will let you add more blood if the sample is insufficient, but many don’t—so it’s best to get it right the first time.

I’ve found that waiting until I have a good-sized drop before touching the strip to it works way better than trying to squeeze more blood out while the strip is already counting down.

Using Expired Test Strips

I’ll admit it—I’ve definitely been guilty of this! Test strips have expiration dates for a reason, and using expired ones can give you inaccurate results. I once found an old container of strips in my drawer and thought, “these are probably fine,” but my readings were all over the place until I replaced them with fresh ones.

Always check:

• The expiration date on the test strip vial
• The date you opened the vial (most are good for 3-6 months after opening)
• That strips are stored properly in their original container with the cap tightly closed

I now write the date on the vial when I first open it, which helps me track when they need to be replaced even if they haven’t technically expired yet.

Storing Test Strips Improperly

Test strips are actually pretty sensitive to environmental conditions! I learned this during a summer camping trip when my strips were exposed to high heat in the car—my readings made no sense until I got home and opened a new vial.

Keep your test strips:

• At room temperature (usually between 59°F and 86°F)
• Away from direct sunlight
• In a dry environment (moisture can damage them)
• In their original container with the lid tightly closed

Some people refrigerate their strips to extend their life, but you need to bring them to room temperature before using them for accurate results. I made this mistake once and got readings that were way lower than my actual blood sugar!

Not Calibrating Your Meter Correctly

Some meters require calibration when you start a new vial of test strips, usually by entering a code or inserting a calibration chip. I once used an entire vial without calibrating and couldn’t figure out why my readings didn’t match lab results at my doctor’s office!

Follow the instructions that came with your meter, and remember that some newer meters automatically calibrate. If your meter requires calibration, do it every time you open a new vial of strips.

Testing on the Wrong Body Sites

While alternate site testing (like forearms or thighs) is possible with some meters, these sites can give different readings than fingertip tests, especially when your blood sugar is changing rapidly. I tried testing on my forearm once when my fingers were sore, and the reading was completely different from what I got from my fingertip just minutes later!

For the most accurate readings:

• Use fingertip testing when your blood sugar might be low or changing quickly
• Only use alternate sites when your blood sugar is stable (like before meals)
• Consult with your healthcare provider before using alternate testing sites

My doctor explained that blood flow to the fingertips shows changes in glucose levels faster than other sites, which is why fingertip testing is generally recommended for the most accurate results.

The Correct Way to Test Blood Sugar

Step 1: Gather Your Supplies

Before starting, I make sure I have everything within reach:

• Blood glucose meter
• Clean, unexpired test strip
• Lancing device with a fresh needle
• Alcohol wipe (if soap and water aren’t available)
• Tissue or cotton ball
• Log book or app to record results

Having everything ready makes the process smoother and helps me develop a consistent routine, which leads to more accurate results over time.

Step 2: Prepare for Testing

Proper preparation makes a huge difference in accuracy:

1. Wash hands thoroughly with soap and warm water
2. Dry completely with a clean towel
3. Make sure your hands are warm (run under warm water if needed)
4. Insert a test strip into your meter and wait for it to turn on and indicate it’s ready
5. Have your lancing device ready with the appropriate depth setting

I find that hanging my hand down and shaking it gently for a few seconds increases blood flow to my fingertips, making it easier to get a good sample.

Step 3: Lance Your Finger and Collect Blood

This part took me the longest to perfect:

1. Place the lancing device against the side of your fingertip (rotate sites to prevent soreness)
2. Press the button to activate the lance
3. Gently squeeze or massage from the base of the finger toward the tip to form a good-sized drop
4. Don’t squeeze too hard right at the puncture site

I’ve learned to use the sides of my fingers rather than the pads, as there are fewer nerve endings there, making testing less painful. I also rotate through all ten fingers to give each one time to heal.

Step 4: Apply Blood to the Test Strip

Timing and technique matter here:

1. Touch the edge of the test strip to the blood drop (don’t smear or push against the skin)
2. Make sure the test area fills completely
3. The meter will begin counting down once it detects sufficient blood

I used to make the mistake of putting the test strip on top of my finger and pressing down—this doesn’t work nearly as well as holding the strip to the side of the blood drop and letting capillary action draw the blood in.

Step 5: Read and Record Your Results

Don’t skip this important step:

1. Wait for the meter to display your reading
2. Record the number, date, time, and any relevant information (like recent meals or activity)
3. Dispose of the test strip and lancet properly

I keep a log with notes about meals, medication, exercise, and stress levels, which helps me spot patterns. This information has been incredibly valuable during doctor appointments!

Special Considerations for Blood Sugar Testing

Testing During Illness

When I’m sick, my blood sugar tends to spike, so I test more frequently. Being ill can dramatically affect your readings, so more frequent monitoring is essential during these times.

Testing Before and After Exercise

Exercise can lower your blood sugar, sometimes dramatically. I always test before, during (for longer sessions), and after working out to avoid dangerous lows. Once, I skipped my post-workout test and ended up with symptoms of hypoglycemia because I didn’t realize how much my workout had affected my levels.

Testing at Different Times of Day

Your doctor might recommend specific testing times based on your condition and treatment plan. Common testing times include:

• Fasting (when you wake up)
• Before meals
• 1-2 hours after meals
• Before bedtime

I’ve found that testing at consistent times helps me understand my body’s patterns and make better decisions about food, medication, and activity.

Conclusion

Learning how to test blood sugar correctly takes practice, but avoiding these common mistakes will give you much more reliable information to manage your diabetes effectively. After years of testing, I’ve realized that accurate readings aren’t just numbers—they’re the foundation for every diabetes management decision I make throughout the day.

Remember that everyone’s experience with diabetes is unique, and what works for me might need adjusting for you. Talk to your healthcare provider about your specific testing needs and any concerns you have about your readings.

What mistakes have you made when testing your blood sugar? Share your experiences in the comments—I’m always looking to learn more tips from others living with this condition!