The benefits and risks of continuous glucose monitors matter because CGMs can dramatically improve day-to-day glucose control, but a wrong sensor reading (or a missed alert) can also lead to dangerous “sugar crashes” or insulin mistakes.
CGMs are still one of the most important diabetes tools we have. The 2026 ADA Standards of Care highlight expanded use of CGM and automated insulin delivery (AID) systems, while also stressing a key safety rule: you must have a blood glucose meter (BGM) available at all times for confirmation when needed.
Searching for a specific answer? Jump to our Frequently Asked Questions for quick tips on exercise safety.
| Situation | What to do (simple rule) | Why it matters |
|---|---|---|
| You feel low, but CGM says normal | Check a fingerstick before treating | CGMs can lag or be wrong; symptoms win |
| CGM shows “LOW” or <70 mg/dL (3.9 mmol/L) and you feel fine | Fingerstick first unless you’re truly symptomatic | False lows can cause overeating or unnecessary insulin reductions |
| CGM shows a high and you’re about to take a big correction | Confirm with BGM if there’s any doubt | False highs can lead to too much insulin and severe hypoglycemia |
| Rapid change (post-meal, exercise, after treating a low) | Expect CGM-to-blood mismatch; confirm if decisions are high-stakes | Interstitial glucose can trail blood glucose during fast changes |
| Using an AID/closed-loop system | Assume CGM errors can drive insulin changes; use confirmation rules more often | AID uses “CGM-informed algorithms” to adjust insulin delivery |
| No readings/signal loss / “sensor error.” | Switch to meter checks until CGM recovers | No data can be as risky as wrong data |
What are the proven benefits of continuous glucose monitors?
CGMs measure glucose in the fluid under your skin (interstitial fluid) and update frequently, giving you trend arrows and alerts. For many people, that “movie” of glucose is more helpful than occasional fingersticks.
- Better glucose control: CGM use is linked to overall glucose levels and helps many people spend more time in range (often referred to as “time in range” rather than just A1C).
- Fewer lows: Alerts and trend arrows can help lower hypoglycemia episodes by catching downward trends early, before a crash occurs.
- Make better decisions about food, insulin, and activity: People can identify patterns such as overnight dips, post-meal spikes, or exercise-related drops, and adjust timing and doses with their clinician’s help.
CGMs may also be linked with improved real-world outcomes beyond glucose numbers. A 2025 study of insulin-treated adults with type 2 diabetes in a large national cohort found that using a CGM was associated with about a 20% lower mortality and fewer clinical events. Even though this is observational and not proof of cause and effect, it suggests meaningful benefits in routine care.
What are the potential issues with CGM readings—and why could that be risky?
CGMs are medical devices, and two things can be true at the same time: they are extremely helpful, and they can occasionally be wrong in ways that matter.
The most serious issues typically fall into four categories:
- False low readings (CGM reads lower than actual blood glucose)
- False high readings (CGM reads higher than actual blood glucose)
- Missed or delayed alerts (you don’t hear/receive a warning)
- Data gaps (no readings due to signal loss or sensor failure)
Even when a CGM is working correctly, values can differ from blood glucose during rapid changes because interstitial glucose may lag behind blood glucose. The 2026 ADA Standards specifically highlight the mismatch risk during fast changes.
How can a “false low” CGM reading harm you?
A CGM that reads low when you’re not actually low can lead you to make the wrong decision:
- Over-treating: Eating extra carbs “just in case” can cause rebound highs.
- Reducing or skipping insulin: If you cut insulin because you think you’re low (but you’re not), you may run high for hours. For insulin-dependent diabetes, this can increase the risk of ketosis or diabetic ketoacidosis (DKA) if sustained.
- AID impact: In an AID system, a false low can cause the algorithm to automatically reduce insulin delivery—helpful when a low is real, but risky if it’s not.
This isn’t just theory. In late 2025, the FDA issued an Early Alert for certain FreeStyle Libre 3 and Libre 3 Plus sensors that might give false low readings. The FDA pointed out that, as of November 14, 2025, Abbott reported 736 serious injuries and seven deaths linked to the issue (reports don’t automatically prove cause, but they are important signals).
How can a “false high” CGM reading harm you?
False highs can push insulin in the wrong direction:
- Insulin stacking: If you correct a “high” that isn’t real, you can cause a true low later.
- Over-correction at night: Nighttime corrections are higher risk because you may not notice symptoms while asleep.
- AID impact: With AID, a false high can automatically drive more insulin. That can be a safety win when the high is real—and a safety risk when it isn’t.
Practical example: If a CGM shows 250 mg/dL (13.9 mmol/L) but your true blood glucose is closer to 140 mg/dL (7.8 mmol/L), a large correction could overshoot and create a severe low.
How frequently do CGM errors and serious adverse events occur?
There are two different ways to talk about “how common” problems are:
- Accuracy in studies: Many CGMs perform well on average and help improve outcomes.
- Real-world failures: Even a low rate of major errors matters because insulin decisions can be high-stakes.
One way to understand real-world failures is the FDA’s MAUDE adverse-event database. A 2025 paper analyzing 2022 MAUDE reports across four CGM families (Dexcom G6, Abbott Libre, Medtronic Guardian 3, Senseonics Eversense) found 281,963 total adverse events, including 268,310 malfunctions, 13,644 injuries, and nine deaths reported that year. This does not tell us the true “error rate” (reporting is incomplete, and denominators aren’t available), but it does show that device issues occur and can be serious.
Why does automated insulin delivery (AID) carry both extra risks and extra benefits?
AID systems can improve time-in-range and reduce glucose variability for many people, but they rely heavily on CGM data. The ADA describes AID as using “CGM-informed algorithms” to adjust insulin delivery.
That means CGM problems can be amplified:
- False low → less insulin (risk of prolonged hyperglycemia, possible ketosis if insulin-deficient)
- False high → more insulin (risk of hypoglycemia)
- Missed alerts or data gaps can delay the “human check” that prevents a small problem from turning into a crisis
Bottom line: AID can be wonderful, but it makes your “when to confirm” rules even more important.
When should you use a blood glucose meter backup with a CGM?
The 2026 ADA Standards are clear: people using CGM must have access to BGM at all times. They list common situations where BGM is needed, including when CGM readings seem inaccurate, during sensor warm-up, when transmission is disrupted, when warning messages appear, when supplies are delayed, and during rapid glucose changes when CGM and blood glucose may not match.
Use this step-by-step rule set:
- Ask: “Does this number match how I feel?” If not, assume the CGM may be off.
- Check your fingerstick before you make a high-impact decision (e.g., a large correction, driving, bedtime, intense exercise, treating a “LOW” when you feel fine).
- Act on the meter value if there’s a mismatch—then troubleshoot the CGM.
- Re-check if needed in 15–20 minutes after treating a low, because CGM lag can make the display “look low” even after blood glucose is rising.
Safety note on thresholds: If you’re using standardized targets, many people consider <70 mg/dL (3.9 mmol/L) as hypoglycemia and <54 mg/dL (3.0 mmol/L) as clinically significant hypoglycemia, but your personal targets should be set with your clinician.
What should you do if you’re worried about missed alerts?
Missed alerts are a real safety issue. In July 2025, the FDA issued a Class I recall for certain Dexcom receivers due to a speaker malfunction that could cause missed alerts for dangerously low or high blood sugar levels. The FDA noted at least 56 reported injuries and no deaths at the time of posting.
Use this practical checklist:
- Test your alert volume (and vibration) after software updates or device changes.
- Check phone settings: Do Not Disturb, Focus modes, Bluetooth permissions, and notification toggles can silence alarms.
- Have a backup plan at night: If you’re high risk for severe lows, consider a dedicated receiver, a louder device, or caregiver sharing options (if you use them).
- When in doubt, test it: If you didn’t hear an alarm but you feel “off,” check a fingerstick.
How can you reduce the risk of CGM errors day to day?
These habits are boring—but they prevent emergencies:
- Use confirmation rules consistently (especially with AID).
- Watch for rapid-change situations where lag is common (after meals, exercise, after treating a low).
- Be cautious with “surprise lows” (especially when you feel fine). Confirm before over-treating.
- Keep a “backup kit”:
- Blood glucose meter + strips + lancets
- Fast carbs for lows
- Glucagon (if prescribed)
- For insulin-dependent diabetes: ketone testing supplies and a sick-day plan
- Pay attention to safety communications (FDA early alerts, corrections, recalls) and follow the manufacturer’s steps for checking affected lots/serial numbers.
Helpful Resources & Research
- ADA Standards of Care in Diabetes—2026 (Diabetes Technology chapter)
- ADA Standards of Care in Diabetes—2026 (Full Supplement Issue)
- Initiation of Continuous Glucose Monitoring and Mortality in Type 2 Diabetes (PubMed)
- Adverse Event Causes From 2022 for Four Continuous Glucose Monitors (J Diabetes Sci Technol PDF)
- FDA Early Alert: Glucose Monitor Sensor Issue from Abbott Diabetes Care (Libre 3 / Libre 3 Plus)
- FDA Safety Communication: Abbott Medical Device Correction (Libre 3 / Libre 3 Plus)
- FDA Recall: Dexcom CGM Receivers (speaker malfunction; missed alerts)
- Drug Delivery Business: Dexcom Updates CGM Receiver Recall (reporting)
- MDDI Online: 7 Deaths Potentially Linked to Faulty Abbott CGM Sensors (reporting)
- Cardiovascular Business: FDA Confirms Recalls; Lawsuit Alleges Abbott Concealed Information (reporting)
Frequently Asked Questions
Are continuous glucose monitors accurate enough to dose insulin without fingersticks?
Most modern CGMs are accurate enough for many day-to-day decisions, but they are not perfect. The 2026 ADA Standards say you should still have a blood glucose meter available at all times and use it when the CGM seems wrong, during warm-up, during signal loss, or when glucose is changing quickly. If symptoms don’t match the CGM, confirm with a fingerstick before making a big insulin decision.
What should I do if my CGM says I’m low, but I feel fine?
Treat this as a “confirm first” moment. Check a fingerstick before eating a lot of carbs or reducing insulin. False lows can cause rebound highs or unsafe insulin adjustments. This is especially important if you use an AID system, as it may automatically reduce insulin based on the CGM reading.
Why does my CGM sometimes read lower at night (compression lows)?
Pressure on the sensor area during sleep can sometimes cause an artificial drop in readings. If you notice a sudden steep decline overnight but feel okay, verify with a fingerstick. Consider adjusting the sensor placement or sleeping position to reduce pressure on the site.
What should I do if my CGM says I’m high but I don’t feel high?
Before “stacking” insulin (taking multiple corrections close together), confirm with a fingerstick if there’s any doubt. A false high can lead to too much insulin and a dangerous low later—especially overnight.
Why do CGM and fingerstick readings differ after meals or exercise?
CGMs measure glucose in interstitial fluid, which can trail behind blood glucose during rapid changes (like after eating, during exercise, or after treating a low). The ADA notes mismatches can occur during rapid glucose changes, so use a fingerstick when the decision is high-stakes.
Is it riskier to use a CGM with an automated insulin delivery (AID) system?
AID systems can be safer and more effective for many people, but CGM errors can have a bigger impact because the algorithm automatically adjusts insulin. The ADA describes AID as using CGM-informed algorithms to modulate insulin delivery, which is why confirmation rules matter even more with AID.
Do I still need a blood glucose meter if I use a CGM?
Yes. The 2026 ADA Standards say CGM users must have access to a blood glucose meter at all times—especially for times when CGM readings may be unreliable (warm-up, signal loss, alerts that don’t match symptoms, and rapid glucose changes).
What’s the risk if my CGM misses alarms?
Missed alarms can delay treatment of dangerous lows or highs. The FDA posted a Class I recall for certain Dexcom receivers due to a speaker malfunction that could cause missed alerts; at the time of posting, at least 56 injuries were reported and no deaths were reported. Make sure your alert settings and device audio are working, especially after updates.
How can I tell if my CGM sensor has been affected by a recall or safety alert?
Check the FDA safety page and follow the manufacturer’s process to verify if your sensor lot or serial number is affected. For example, the FDA issued an Early Alert and safety communications concerning incorrect low readings for certain FreeStyle Libre 3 / 3 Plus sensors. If your sensor is affected, stop using it and use a meter for decisions until you receive a replacement.
Last Updated on January 21, 2026
