What are the different types of glucose monitors?

There are several types of glucose monitors used for managing diabetes or monitoring blood sugar levels. These devices generally fall into 2 categories:

• Blood glucose meters (BGM)
• Continuous glucose monitors (CGM)

Different types of glucose monitors

1. Blood glucose meters (BGM)
   • BGMs are the traditional method for measuring blood glucose levels.
   • How They Work:
     • A lancet pricks the skin to collect a small blood sample.
     • The blood sample is applied to a test strip.
     • The test strip reacts with the glucose in the blood.
     • The meter processes the result and shows your glucose level.
   • Reliability:
     • BGMs are generally reliable if used correctly.
     • The accuracy of BGMs is regulated by health authorities, such as the FDA.
     • Most devices are accurate within 15–20% of actual glucose levels. However, results can be affected by user error (e.g., not following instructions, using expired test strips, or improper handling of samples).
   • Limitations:
     • BGMs provide a snapshot of your glucose level at a specific moment. They do not track trends or fluctuations in glucose over time unless multiple tests are performed throughout the day.
2. Continuous glucose monitors (CGM)
   • CGMs provide real-time monitoring of glucose levels throughout the day and night. They track changes in glucose levels continuously, typically every few minutes, by measuring the glucose in the interstitial fluid (the fluid between cells) rather than directly from blood.
   • How They Work:
     • A small sensor is inserted under the skin, typically in the abdomen or arm.
     • The sensor measures glucose levels in the interstitial fluid.
     • A transmitter sends the data to a receiver, smartphone, or smartwatch, providing continuous glucose readings.
     • Some CGMs also have alarms that notify the user when glucose levels are too high or too low.
   • Reliability:
     • CGMs tend to be accurate, but they are typically not as precise as BGMs because they measure glucose in the interstitial fluid, which can lag behind blood glucose levels by a few minutes.
     • The newer CGMs have improved in accuracy, with some showing readings within 10–15% of blood glucose levels.
   • Limitations:
     • Since CGMs measure glucose in interstitial fluid, they may have a slight delay compared to blood glucose meters, particularly during rapid changes in glucose.
     • Calibration may also be needed for some CGMs, although some newer models are factory-calibrated and do not require manual calibration.
3. Flash glucose monitors (FGM)
   • FGMs are a hybrid of traditional blood glucose meters and continuous monitoring systems.
   • How They Work:
     • A sensor is placed under the skin, similar to a CGM.
     • The sensor records glucose levels continuously.
     • The user must scan the sensor with a reader or smartphone to view their glucose data. Unlike CGMs, flash glucose monitors do not have real-time alerts.
   • Reliability:
     • FGMs tend to have similar accuracy to CGMs, with some models showing reliable glucose readings that are close to actual blood glucose levels.
   • Limitations:
     • There are no alarms for high or low glucose levels.
     • As with CGMs, the readings are based on interstitial fluid, so there may be slight delays during rapid glucose changes.
4. Non-invasive glucose monitors
   • Non-invasive glucose monitors aim to measure blood glucose levels without using blood samples or sensors under the skin. These devices are still in development, and none have yet reached widespread clinical use or approval.
   • How They Work:
     • These devices use technologies like infrared light, ultrasound, or electromagnetic waves to estimate glucose levels by scanning the skin or other body tissues.
   • Reliability:
     • The accuracy of non-invasive glucose monitors is still under research.
     • Most of these devices have yet to meet the standards required for reliable, consistent glucose measurement.

Key factors affecting reliability

• Calibration – some devices, especially CGMs, require periodic calibration with blood glucose meter readings to maintain accuracy.
• User error – for both BGMs and CGMs, improper technique (e.g., incorrect use of test strips, contamination of the sensor, or failure to follow maintenance protocols) can lead to inaccurate readings.
• Environmental factors – temperature, humidity, and altitude can affect the performance of both BGMs and CGMs.
• Sensor Longevity – CGMs have a limited lifespan (usually 7 to 14 days), and older sensors may provide less accurate results.

The choice of monitor depends on your needs – whether you need frequent monitoring, trend tracking, or simple periodic checks. Always consult with your healthcare provider to choose the best option for your personal management of diabetes or blood sugar monitoring.

References

Mathew TK, Zubair M, Tadi P. Blood Glucose Monitoring. [Updated 2023 Apr 23]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK555976/

Seidu S, Kunutsor SK, Ajjan RA, Choudhary P. Efficacy and Safety of Continuous Glucose Monitoring and Intermittently Scanned Continuous Glucose Monitoring in Patients With Type 2 Diabetes: A Systematic Review and Meta-analysis of Interventional Evidence. Diabetes Care. 2024 Jan 1;47(1):169-179