Continuous glucose monitoring (CGM) devices have changed the way many people manage diabetes. Instead of relying exclusively on periodic fingerstick testing, patients can use a sensor to receive ongoing information about glucose levels and trends. For many patients, that information guides decisions about insulin, food, exercise, and when to seek medical attention. But what happens when the information is wrong?
An inaccurate glucose reading can be more than a minor inconvenience. A patient who relies on incorrect data may make a treatment decision that causes a dangerous change in blood sugar. In some circumstances, the resulting hypoglycemia or hyperglycemia can lead to hospitalization, loss of consciousness, neurological injuries, falls, motor vehicle crashes, or other serious harm.
The potential risks are not merely theoretical. In 2025, Abbott initiated a medical device correction affecting certain FreeStyle Libre 3 and FreeStyle Libre 3 Plus sensors after internal testing found that some sensors could provide incorrect low glucose readings. The FDA subsequently classified the action as a Class I recall, the FDA’s most serious device recall classification.
How Continuous Glucose Monitors Work
A continuous glucose monitor uses a sensor placed under the skin to measure glucose in the interstitial fluid. The sensor sends information to a reader, smartphone application, or other compatible device, allowing the patient to monitor glucose levels and trends.
CGMs can provide information that traditional blood glucose testing cannot easily provide, including whether glucose is rising or falling and how quickly those changes are occurring. That information can be particularly valuable for patients who experience fluctuations in blood sugar or episodes of hypoglycemia without obvious warning symptoms.
Because patients use these readings to make real-time decisions, accuracy is critical. A CGM that consistently provides reliable information can become an integral part of a person’s diabetes management. Conversely, an inaccurate device can cause a patient to act on information that does not reflect their actual blood glucose level.
What Happens When a CGM Gives an Incorrect Reading?
The danger of an inaccurate CGM reading comes from what happens next. The patient generally does not simply observe the number on the screen; they respond to it. For example, a device that falsely reports low glucose could lead a patient to consume carbohydrates, delay insulin, or reduce an insulin dose. If the patient’s actual glucose level is significantly higher than the device indicates, those decisions could contribute to dangerous hyperglycemia.
The opposite problem can also occur. A falsely high glucose reading may cause a patient to administer additional insulin when their actual glucose level is normal or already falling. Excessive insulin can cause severe hypoglycemia.
The FDA has specifically warned that inaccurate FreeStyle Libre 3 readings can lead to incorrect treatment decisions. For certain recalled sensors, the concern involved readings that were lower than actual blood glucose levels, potentially causing excessive carbohydrate intake or skipped or delayed insulin doses.
False Low Readings Can Lead to Dangerous Treatment Decisions
A false low reading can be particularly deceptive because the patient may believe the CGM is alerting them to an immediate hypoglycemic episode. If the patient’s actual glucose is substantially higher than the displayed reading, the patient may consume unnecessary carbohydrates or avoid taking insulin. If the inaccurate reading continues for hours, the resulting treatment decisions may contribute to prolonged hyperglycemia.
In its recall information concerning certain FreeStyle Libre 3 and Libre 3 Plus sensors, the FDA stated that incorrect low readings could result in treatment decisions that pose risks of serious injury or death. The FDA’s recall database identifies a manufacturing-process issue involving certain affected sensors. The FDA reported that the issue could cause carbon buildup in the sensor and result in incorrect low glucose results.
False High Readings Can Also Cause Serious Harm
A CGM error does not have to produce an artificially low reading to be dangerous. In July 2024, Abbott announced a medical device correction affecting a small subset of FreeStyle Libre 3 sensors after internal testing determined that some sensors could provide incorrect high glucose readings. Abbott warned that inaccurate high readings could result in patients taking insulin when it was not required.
The FDA’s recall information explained the potential consequences in greater detail. Incorrectly high glucose readings could cause patients to calculate larger insulin correction doses than appropriate. Excess insulin can produce severe hypoglycemia, including a potentially life-threatening hypoglycemic crisis.
This illustrates why the safety of a CGM cannot be evaluated simply by asking whether the device produces readings that are “close” to the patient’s actual glucose level. A sufficiently inaccurate reading can change the treatment decision a patient makes.
What Injuries Can Result From an Incorrect Glucose Reading?
The consequences of a CGM error depend on the circumstances, including how inaccurate the reading is, how long the error continues, the patient’s underlying medical condition, and what treatment decision follows from the inaccurate information. Potential complications can include severe hypoglycemia or hyperglycemia and the medical emergencies associated with those conditions. A patient who becomes confused, dizzy, weak, or unconscious may also suffer secondary injuries. For example, a person experiencing severe hypoglycemia could fall and sustain a traumatic brain injury or fracture. If a glucose-related emergency occurs while someone is driving, the resulting impairment could contribute to a motor vehicle collision. A prolonged or severe glucose abnormality can also result in hospitalization and potentially permanent neurological injury.
Not every inaccurate reading will cause an injury. But when an inaccurate reading results in a harmful treatment decision, the consequences can be significant.
The Difference Between a Device Error and a Patient Error
When a patient is injured after relying on an inaccurate CGM reading, it is important not to assume that the patient simply made a mistake. CGM systems are complicated medical devices involving sensors, electronics, software, algorithms, communications between components, and manufacturing processes. An inaccurate result may have a number of potential causes.
The FDA’s recall records concerning FreeStyle Libre devices demonstrate that inaccurate readings can arise from problems associated with the manufacturing process or the device itself. FDA adverse-event reports also document instances in which users reported clinically significant discrepancies between CGM readings and blood glucose meter results. At the same time, not every report of an inaccurate reading establishes that a device was defective. Investigations may determine that a particular sensor was functioning as designed or that another factor contributed to the discrepancy. That distinction can be important when evaluating a potential product liability claim.
Why Patients May Not Realize Their CGM Is Wrong
One reason CGM errors can be particularly dangerous is that patients have a reasonable basis for trusting their medical devices. A person may have used the same type of sensor for months or years without experiencing a problem. The device may provide readings continuously and automatically, creating an expectation that the information on the screen accurately reflects what is happening inside the body. A patient may therefore be more likely to act on a CGM reading than question it.
The FDA has recognized the importance of comparing CGM readings with a patient’s symptoms and expectations. Its safety information for the FreeStyle Libre system states that when readings or alarms do not match symptoms or expectations, users should use a fingerstick blood glucose measurement for treatment decisions.
What Should You Do After a Suspected CGM Error?
If a patient believes a CGM is providing inaccurate information, medical care should take priority. Patients should follow the instructions provided by their healthcare provider and the device manufacturer concerning confirmation of unexpected readings and treatment decisions. It is also important to preserve evidence if a serious injury occurred. Patients and families should consider keeping the sensor, packaging, lot or serial information, reader or compatible device, relevant application information, and communications with the manufacturer. Medical records, blood glucose meter readings, screenshots, alerts, and other documentation may also help establish what happened. The FDA’s recall information provides an example of why identifying the particular sensor matters. The 2025 Class I recall involved specific FreeStyle Libre 3 and Libre 3 Plus sensors rather than every device in the product family.
Can a Defective CGM Lead to a Product Liability Claim?
When a medical device causes an injury, several potential product liability theories may need to be considered. Depending on the facts, a claim could involve an alleged manufacturing defect, design defect, inadequate warnings or instructions, or another product-related issue.
Proving such a claim requires more than demonstrating that a patient received an inaccurate reading. The investigation may need to determine what the device reported, what the patient’s actual glucose level was, what treatment decision followed, why the discrepancy occurred, and how the resulting treatment caused the injury. Evidence concerning the particular sensor can be especially important. A product liability investigation may also involve manufacturing records, complaint histories, adverse-event reports, recall information, testing records, and other evidence concerning the device.
The FDA’s MAUDE database, for example, contains reports involving clinically significant discrepancies in FreeStyle Libre 3 Plus readings. One report described a sensor reading of 41 mg/dL compared with a meter reading of 474 mg/dL. Another described a CGM reading of 66 mg/dL compared with a meter reading of 269 mg/dL, with the manufacturer determining that the sensor may not have met product design specifications. These reports do not by themselves establish liability, but they illustrate the types of evidence that may be relevant when investigating alleged CGM errors.
Contact Leandros A. Vrionedes, P.C. After a Serious CGM Injury
Continuous glucose monitoring devices are intended to help patients manage serious medical conditions, and patients have a right to expect accurate information from the devices on which they rely. When an inaccurate glucose reading contributes to a serious injury, determining what caused the error can be critical.
If you or a family member suffered a serious injury after relying on inaccurate information from a FreeStyle Libre 3, FreeStyle Libre 3 Plus, or another continuous glucose monitoring device, Leandros A. Vrionedes, P.C. can investigate the circumstances and help determine whether a product liability claim may be appropriate. Contact Leandros A. Vrionedes, P.C. to discuss your situation and learn more about your legal options.