Why is my CGM Inaccurate? - Inaccurate readings leads to misinterpretation

Many users have voiced concerns about CGMs showing inaccurate readings, which can affect important decisions about diabetes care. At Gurucose, we’ve dug into the sensor data and reviewed how different apps work to understand why these errors happen and how you can improve your readings.

How do CGMs work?

CGMs measure glucose in the fluid under your skin instead of directly from your blood like fingersticks do (read more here). This causes a natural delay of about 9 minutes during quick changes. After eating, your CGM might show a spike 10–15 minutes later than a fingerstick. While blood glucose monitors are within ±15% accuracy 95% of the time, CGMs are within ±20% about 87% of the time. Newer models like Dexcom and Freestyle Libre perform a bit better, but fingersticks still lead in accuracy.

Extreme temperatures can also alter the sensor’s chemistry. When it’s too hot (above 45°C) or too cold (below 10°C), you might see false high or low readings.

Why do different apps show different readings?

Each app uses its own algorithm to process the raw sensor data. This means the same sensor can show slightly different readings on different platforms.

How can Gurucose improve sensor accuracy?

The Gurucose app lets you enter manual readings to adjust the sensor data. By inputting your actual sugar levels every 2 days, we can calibrate our graphs to match your true values - a key step for Type 1 diabetics managing their insulin doses.

Lastly, make sure your sensor is firmly attached to your skin. Using extra adhesive tape can help keep it in place, leading to more reliable readings.

If you haven’t already, download the Gurucose app from the App Store or Play Store and connect your CGM for more accurate diabetes management insights!