When Ambiguous Device Messaging Becomes Life-Threatening

February 2026

The FDA issued an early alert last week about Trividia Health's TRUE METRIX blood glucose monitoring systems. All models are subject to a labeling correction affecting devices distributed across the United States, UK, Mexico, Australia, and the Caribbean.

The issue? An error code that means two completely different things, and instructions that didn't make the life-threatening scenario clear enough.

Since the product launched in August 2014, there have been 114 serious injuries and one death associated with this labeling problem. That's over a decade of use before the messaging issue was corrected.

This isn't a story about a hardware defect or a software bug. It's about something more fundamental and harder to catch: ambiguous communication in a life-critical device.

When One Error Code Means Two Different Things

The TRUE METRIX system displays an "E-5" error code in two scenarios:

1. A very high blood glucose reading (above 600 mg/dL), which is a medical emergency

2. A test strip error, which is an equipment problem

Think about that from a user experience perspective. You're a person with diabetes. You prick your finger, apply blood to the test strip, and your meter displays "E-5." What does that mean?

Is your blood sugar dangerously high and you need to get to an emergency room immediately? Or did you just get a bad test strip and need to try again with a new one?

The original instructions apparently didn't make this distinction clear enough. Users might see the E-5 code, assume it was a test strip problem, retest, and delay seeking medical attention during an actual hyperglycemic crisis.

The corrected labeling now emphasizes: if you get an E-5 error code AND you're experiencing symptoms of high blood glucose (fatigue, excessive urination, thirst, blurry vision), seek medical attention immediately. Retest with a new strip. If the error persists and symptoms are present, this is an emergency.

That's a critical distinction that should have been impossible to miss in the original instructions.

The Error Code Overloading Problem

Using a single error code to represent multiple failure modes is a known antipattern in embedded systems design, but it happens all the time because it seems efficient. You have limited display space. You want to keep the error code list simple. So you group related errors under one code.

But in a medical device where one scenario is "try again" and the other is "seek emergency medical care," that efficiency creates dangerous ambiguity.

Better design patterns exist. You could use different error codes (E-5 for critical high glucose, E-6 for test strip error). You could display different messages with more context ("CRITICAL: Very High Glucose" vs. "Test Strip Error"). You could use visual indicators (flashing red for medical emergency, steady yellow for equipment issue).

The constraint here is display real estate and keeping the device simple enough for a broad user base. Blood glucose meters need to be usable by elderly patients, people with vision problems, users with varying levels of health literacy. You can't make the interface too complex.

But there's a difference between simple and ambiguous. Simple means the user understands exactly what's happening with minimal cognitive load. Ambiguous means the user has to guess or remember details from the manual.

In this case, the ambiguity had real consequences. 114 serious injuries and a death over 12 years suggests this wasn't an edge case that only affected a handful of users in unusual circumstances.

User Interface Design for Life-Critical Devices

Medical device UI design has to account for use under stress, by users who may be impaired (low blood sugar affects cognitive function), in environments with distractions, by people who haven't read the manual in years or never read it at all.

The baseline assumption should be: the user will not remember what each error code means. The device needs to communicate clearly at the moment of use, not rely on the user's memory of page 47 of the owner's manual.

This is why modern medical devices are moving toward plain language messaging, contextual help screens, and visual/audio cues that differentiate between "informational," "warning," and "critical" states.

For a blood glucose meter, this could look like:

Test strip error: Steady yellow light, message "Strip Error - Try New Strip," single beep

Critical high glucose: Flashing red light, message "Critical: Very High Glucose - Seek Medical Attention," repeated alarm beeps

Different sensory modalities (visual, auditory, textual) working together to eliminate ambiguity, especially for the life-threatening scenario.

The engineering challenge is doing this within the constraints of a low-cost consumer device. Blood glucose meters operate in a price-sensitive market. Adding a color display, better speaker, more sophisticated error handling all increase BOM cost. But when you're designing a device that people depend on to avoid diabetic emergencies, these aren't optional features. They're safety requirements.

The Labeling vs. Design Question

Trividia's response to this issue was a labeling correction, not a device recall or firmware update. The devices continue to work exactly as they did before. Only the instructions have changed.

This raises an interesting question: is this fundamentally a labeling problem, or is it a design problem that's being addressed with updated labeling?

The device behavior (displaying E-5 for two different conditions) hasn't changed. The hope is that better instructions will help users interpret the error code correctly and take appropriate action.

But consider the reality of how labeling updates work in practice. The company sends notifications to distributors and healthcare providers. Updated owner's booklets become available online. Retail pharmacies are supposed to post notices where the devices are sold.

Meanwhile, hundreds of thousands of these meters are already in people's homes, many purchased years ago. How many users will see the updated labeling? How many will go online to download the new owner's booklet? How many even kept the original owner's booklet?

The more robust solution would have been a firmware update that changes how the error codes work, or even a hardware recall to replace the devices with units that have clearer messaging. But that's expensive and logistically complex, especially for a mature product with a large installed base.

So we end up with a labeling correction, which is the regulatory path of least resistance but potentially leaves many users with the same ambiguous error code and outdated instructions.

What This Means for Device Development

The TRUE METRIX case highlights several principles that should inform medical device development:

• Error codes and alerts need unambiguous mapping to user actions. If an error state requires immediate medical intervention, that needs to be unmistakably clear in the moment, not buried in documentation. Different error states should have different visual/auditory signatures, especially when one is life-threatening.

• User interface design is a safety-critical function, not just a usability concern. For medical devices, how you communicate system state to the user directly impacts clinical outcomes. UI design needs to be part of your risk management process, with the same rigor you'd apply to hardware failure modes or software bugs.

• Test your device messaging with actual users in realistic conditions. Not just in a controlled usability study, but with attention to how people actually use the device at home, when they're stressed, when they're not feeling well, when they haven't looked at the manual in months. Ambiguities that seem minor in a lab become critical in the field.

• Plan for long product lifecycles and distributed user bases. If your device will be in use for 10+ years and you can't push firmware updates, you need to get the messaging right the first time. Labeling corrections are hard to propagate to users who bought the device years ago.

• Consider the full context of use. Blood glucose meters are often used by people who are actively experiencing the symptoms of dysglycemia, which affects cognitive function. Your interface needs to work for users whose ability to interpret complex information may be compromised.

• Build in redundancy for critical alerts. If a single piece of information (like "seek medical attention immediately") is the difference between a routine equipment issue and a medical emergency, that information should be communicated through multiple channels: visual, auditory, textual, and with enough prominence that it can't be easily missed or misinterpreted.

The Firmware and Cloud Connectivity Angle

One thing that's notably absent from this story: the ability to remotely update the device's behavior.

Modern connected medical devices can receive firmware updates that change how they operate, including how they display error messages and alert users to critical conditions. If the TRUE METRIX systems had this capability, Trividia could have pushed an update that changes E-5 to display different messages or use different error codes for the two scenarios.

But blood glucose meters have historically been standalone devices with no network connectivity. The TRUE METRIX GO and TRUE METRIX AIR models have Bluetooth for syncing data to a smartphone app, but that's typically one-way communication for data logging, not a mechanism for firmware updates.

There's a trade-off here. Adding update capability means more complex firmware architecture, over-the-air update mechanisms, security to prevent malicious firmware modifications, regulatory clearance for the update process itself, and all the infrastructure to manage updates across a device fleet.

For a $10-30 consumer glucose meter, that's a significant engineering and cost burden. But the ability to fix issues like this across your entire installed base, rather than relying on labeling corrections that may never reach many users, could be worth it from a safety and liability perspective.

The trend in medical devices is toward connectivity and updateability, even for traditionally standalone products. Part of the calculation is exactly this scenario: when you discover a safety issue that can be fixed in software or messaging, can you actually reach all the affected devices?

Documentation as a Last Line of Defense

Updated labeling and owner's manuals are important, but they shouldn't be your primary safety mechanism. Most users don't read manuals cover to cover. They learn the basic operation and only consult the manual when something goes wrong.

In this case, the user who gets an E-5 error code may flip to the troubleshooting section, see "E-5: Test Strip Error or Very High Blood Glucose," and if the message doesn't immediately scream "EMERGENCY," they might treat it as a routine equipment issue.

Good device design makes critical safety information impossible to miss at the point of use. The device itself should communicate urgency through its interface, not rely on the user's memory of documentation they may have read once (or never).

This is especially true for home-use medical devices where there's no trained operator or clinical supervision to catch interface ambiguities and guide users to the correct interpretation.

Looking Forward

The medical device industry is full of products that have been on the market for years or decades with user interfaces that haven't kept pace with what we now know about human factors engineering and safety-critical communication.

Many of these devices work fine most of the time. But edge cases, ambiguous states, and scenarios where users need to make time-critical decisions based on device output are where interface design failures turn into adverse events.

For companies developing the next generation of medical devices, the lesson from the TRUE METRIX situation is clear: invest in getting your user interface, error handling, and safety messaging right from the beginning. Test ruthlessly with real users in realistic conditions. Assume users won't read the manual or remember its details. Design your device to be unambiguous in critical situations.

And if you can build in the capability to update your devices in the field, do it. The ability to fix issues across your installed base without relying on labeling corrections that may never reach end users is increasingly essential.

"Because 114 serious injuries and a death over 12 years from an ambiguous error code is 114 too many."

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At MedTechWare, we design medical device firmware and user interfaces with safety as the foundation. From error handling and alert systems to human factors testing and regulatory documentation, we build devices that communicate clearly in critical moments. Whether you're developing connected diagnostics, home-use devices, or any medical technology where user interpretation affects outcomes, we have the expertise to get it right the first time.

Ready to build medical devices with unambiguous, safety-first interfaces? Contact us to discuss your project.

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MedTechWare is a medical device software and hardware product development company specializing in embedded solutions, cloud platforms, and regulatory compliance for the medical and biotech industries.