Top 5 common CGM mistakes and how to avoid them - Vively

Jul. 21, 2025

Top 5 common CGM mistakes and how to avoid them - Vively

Are you making common CGM mistakes without realising it? Small errors in sensor placement, skin prep, or calibration can throw off your readings and impact your diabetes management. The good news? A few simple tweaks can make all the difference.

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Key takeaways

Correct sensor placement, skin preparation, and calibration are crucial for accurate CGM readings and effective diabetes management.
External factors such as temperature, altitude, and hydration can affect CGM accuracy, requiring adjustments for reliable data.
Understanding trends and patterns in CGM data is more important than focusing on individual readings, leading to better long-term health decisions.

Mastering your CGM isn't just about wearing the sensor—it's about understanding how placement, preparation, and external factors influence your readings. When you focus on trends rather than isolated numbers, you'll gain better control over your glucose levels and make smarter health choices.

Introduction

CGMs (Continuous Glucose Monitors) can dramatically improve blood sugar management, but users often make mistakes that affect accuracy and data interpretation. Here's a quick guide to avoid the top 5 CGM pitfalls:

Incorrect sensor placement

Poor skin preparation

Improper calibration

Ignoring external factors

Misunderstanding CGM data

By avoiding these mistakes, you'll get more accurate readings and make smarter health choices. Let's break it down:

Remember: CGMs have a 2-15 minute lag between actual blood sugar and sensor readings. They're great for spotting trends, but not always 100% accurate. Use them wisely, and you'll see big improvements in your diabetes management.

1. Placing the sensor incorrectly

Bad sensor placement can mess up your glucose readings. Here's why it matters and how to get it right.

Why wrong placement is a problem

1. Off-target readings: Sensors on muscle-heavy or fat-light areas can give wonky numbers.

2. Broken sensors: Putting them where they'll get knocked around? That's asking for trouble.

3. Angry skin: Using the same spot too often? Hello, rashes and infections.

Nailing the right placement

Here's your game plan:

1. Choose your spot wisely:

Dexcom G6: Adults, go for the belly. Kids, aim for lower back or upper buttocks.

FreeStyle Libre: Back of upper arm, always.

Medtronic Guardian Connect: Belly or back of upper arm.

2. Prep work:

Clean with alcohol, let it dry.

Got hair? Maybe shave it.

3. No-go zones:

Keep 3 inches from pump sites or injection spots.

Avoid scars, tattoos, and irritated skin.

4. Mix it up: Don't use the same spot twice in a row.

5. RTFM: Each CGM has its own quirks. Read the manual. Good placement = accurate readings.

2. Not preparing the skin properly

Poor skin prep can wreck your CGM experience. Here's why it matters and how to do it right.

Problems from poor skin prep

1. Sensor falls off

2. Skin irritation

3. Inaccurate readings

How to prepare your skin

1. Clean thoroughly:

Use oil-free, antimicrobial soap and water. Got oily skin? Gently exfoliate.

2. Dry completely:

Pat dry with a towel. In humid areas, use a cool hairdryer.

3. Use barriers:

Apply a liquid barrier film to protect sensitive skin.

4. Consider antiperspirant

For sweaty areas, apply unscented antiperspirant around (not on) the insertion site.

5. Tackle allergies

Sensitive to adhesives? Try these:

Spray Flonase on skin before inserting sensor

Apply a Band-Aid Tough Pad first, then insert sensor through it

Everyone's skin is different. You might need to experiment. A study found 80% of paediatric CGM users had skin issues: 70% pruritus, 46% eczema, and 33% wounds. But with proper prep, you can avoid joining these stats.

3. Calibrating incorrectly

Calibration can make or break your CGM accuracy. Let's dive into why it's crucial and how to get it right.

Why calibration matters

Poor calibration leads to:

Wonky glucose readings

Bad diabetes management choices

Unnecessary stress

Take the Dexcom G7. It's got a 9% error margin compared to lab results. But mess up the calibration, and that number skyrockets.

Nailing your calibration

1. Read the manual

Every CGM is different. The Dexcom G6? It calibrates itself on the first day. The MiniMed? You're looking at 3-4 calibrations daily.

2. Pick the right moment

Don't calibrate when:

You're eating or just finished a meal

You're fixing a high or low

Your CGM shows rapid changes (two arrows)

3. Clean hands = clean data

Soap and water before fingersticks. It's that simple.

4. Fresh strips are your friend

Check those expiration dates. Old strips = bad news.

5. Speed is key

For systems like the MiniMed, punch in those new BG readings ASAP.

6. Don't go overboard

Stick to the recommended number of calibrations. More isn't always better.

7. Trust your gut

CGM not matching how you feel? Do a fingerstick check.

Here's the deal: Even perfect calibration won't make your CGM match fingersticks exactly. A 20% difference? That's normal. But good calibration keeps you in the ballpark.

4. Ignoring outside factors

Your CGM doesn't live in a bubble. The world around you can mess with your readings. Let's look at how and what to do about it.

Outside actors and your readings

1. Temperature

Hot days can throw your CGM off:

Heat speeds up insulin absorption

You get dehydrated faster

Your body uses insulin differently

2. Altitude

‍Mountain trips? Your CGM might act up:

Less oxygen affects sensor accuracy

Pressure changes impact readings

3. Dehydration

‍Not enough water? Your CGM notices:

Less fluid in veins = weird blood sugar concentrations

High blood sugar makes dehydration worse

Tackling outside factors

1. Beat the Heat

Check blood sugar more on hot days

Drink tons of water

Exercise when it's cooler

2. Handle High Altitudes‍

Give CGM time to adjust (about 24 hours)

Double-check with finger sticks more

Stay extra hydrated

3. Stay Hydrated‍

Aim for clear or light yellow urine

Eat water-rich foods

Track intake on hot days

4. Watch for Sneaky Factors

Your CGM is a tool, not a crystal ball. Use it with your body knowledge and environment awareness for best results.

5. Misunderstanding CGM data

CGM devices flood you with blood sugar information. But it's easy to get lost in the numbers. Here's how to make sense of your CGM data:

Common data misunderstandings

Single reading fixation: Don't freak out over one high or low number. Look at the big picture.

Ignoring trend arrows: These show where your blood sugar's heading. Use them to make smart choices.

Forgetting lag time: CGMs measure skin sugar, not blood sugar. There's a delay.

‍Missing patterns: Daily ups and downs are normal. Watch for repeat offenders.

Using CGM data effectively

1. Track Time in Range (TIR)

TIR is the percentage of time your blood sugar's between 3.9-10.0 mmol/L. It's a diabetes management powerhouse.

2. Use the DATAA model

This helps you crack the CGM code:

Download data

Assess safety

Time in range

Areas to improve

Action plan

3. Spot patterns

Check at least 14 days of CGM data. It's your glucose behaviour roadmap.

4. Team up with your doctor

Don't go solo. Your healthcare team can help you decode data and make smart moves.

5. Mind the lag

There's a 2-15 minute delay between your actual blood sugar and your CGM reading. Keep that in mind when making decisions.

Conclusion

CGM technology is a game-changer for diabetes management. But it's not foolproof. Here's a quick rundown of the 5 CGM pitfalls and how to sidestep them:

1. Sensor placement: Stick to recommended spots, rotate sites

‍2. Skin prep: Clean and dry before applying

‍3. Calibration: Follow manufacturer's timing and frequency guidelines

‍4. Outside factors: Watch for temperature and medication effects

‍5. Data interpretation: Focus on trends, not single readings

‍Keep in mind: CGM isn't instant. There's a 2-15 minute lag between blood sugar and sensor readings.For a deeper dive into how blood sugar impacts hormonal health and how CGM data can help you optimise your diet, exercise, and lifestyle, check out our blog on balancing hormones naturally with a CGM.

But here's the good stuff. CGM can seriously up your diabetes management game:

Just remember, CGM accuracy can vary:

The takeaway? CGM is powerful, but it's not magic. Use it right, and you'll see results. As Charlotte Battle, Vively’s dietitian, says:

‍

“A CGM gives you the data, but real change comes from how you use it. Focus on patterns, make small adjustments, and build habits that support your long-term health.”

So, dodge these common mistakes, and you'll be on track for better diabetes management with CGM.

More information

Vively's CGM program and app help you avoid common CGM mistakes. Here's how:

Real-time data: Vively works with Freestyle Libre sensors to give you instant glucose info. This helps you spot trends fast and make quick changes.
Smart advice: The app doesn't just show numbers. It gives you tips based on your glucose, diet, exercise, and sleep. This helps you see how different things affect your glucose.
Expert help: Confused about your data? No problem. You can chat with dietitians in the app for personalised advice.
Easy to use: The app is simple to navigate. You can easily log meals and activities and check your glucose trends.
Deep analysis: Vively does more than just track glucose. It lets you:

Keep sensors safe: Vively gives you two patches to keep your sensor in place during exercise and showers. This helps avoid a big CGM mistake: losing your sensor.
Clear setup: The app walks you through putting on the sensor, so you get it right.
‍Alerts: Get warnings on your if your glucose is going too high or low, helping you stay healthy.

FAQs

Why is my CGM so inaccurate?

CGMs can be inaccurate for a few reasons:

Sleeping on your sensor (false lows)

Extreme temperatures and humidity

Wrong sensor placement

Dehydration

To boost accuracy:

Switch up sensor spots

Drink enough water

Avoid hot or cold extremes

Do a finger-stick test if something seems off

Can CGM give false readings?

Yep, CGMs can give false readings. Here's the scoop:

CGMs can be off by up to 20% compared to finger-stick tests

CGMs measure interstitial fluid, not blood glucose

Some meds (like Tylenol) can mess with CGM readings

If you think your CGM's lying:

Do a finger-stick test

Chat with your healthcare provider

Maybe swap out the sensor

‍Bottom line: CGMs are great for trends, even if they're not always spot-on.

‍Vively is a metabolic health app that can help women undergoing the menopause transition improve their quality of life. The Vively app integrates with continuous glucose monitors (CGM) to help women understand how their lifestyle is impacting their blood sugar levels. This, combined with in-app education and support can help women improve their symptoms. Chat to your doctor about whether Vively may suit you.

If you are looking for more details, kindly visit CGM Patches.