Flash glucose monitoring (FGM)
Flash glucose monitoring (FGM) is a system for continuous glucose monitoring without constant finger pricking. The best known representative is this Freestyle Libresystem from Abbott. Important: Freestyle Libre 1 and 2 are classic FGM (scan systems), while Freestyle Libre 3 is already a real one rtCGM (real-time CGM) is – just like Dexcom G7 or Guardian 4.
How it works
A small, waterproof sensor is inserted painlessly into the subcutaneous fatty tissue (usually the upper arm). It measures the glucose concentration every 15 minutes and saves the data. With classic FGM (Libre 1/2), the sensor must be actively scanned to see the values. With Libre 3 and rtCGM systems, the values are transferred automatically.
Difference FGM vs. rtCGM (Freestyle Libre 2 vs. Libre 3 vs. Dexcom)
| feature | FGM (Freestyle Libre 1 & 2) | rtCGM (Freestyle Libre 3, Dexcom G7, Guardian 4) |
|---|---|---|
| Data transfer | Only when scanning manually | Automatically every 5 minutes on your smartphone |
| Alarms | No automatic alarms | Yes – alarm for hypo/hyper (even at night) |
| History | Just the last 8 hours | Full history (up to 90 days retroactively) |
| Accuracy with rapid changes | Good, but with a 5-15 minute delay | Higher accuracy, faster |
| Costs | Cheaper | More expensive |
| Particularly suitable for | Patients who are actively scanning and do not need alarms | Patients with hypo-perceptual disorder, sports, children, night safety |
Benefits of FGM (Libre 1 & 2)
- Very comfortable - no regular stinging
- Trend arrows and progression visible
- Good overview of patterns
- Cheaper than most rtCGM systems
Further information:
Further information:
→ Diabetes mellitus – knowledge and overview
→ Why hyporest
→ Continuous glucose monitoring (CGM)
Sources
- German Diabetes Society (DDG). S3 guideline “Technological aids in diabetology”. As of 2025.
- American Diabetes Association. Standards of Medical Care in Diabetes—2026.
- Robert Koch Institute (RKI). Federal health reporting – diabetes mellitus in Germany. Berlin 2024.
- International Diabetes Federation (IDF). IDF Diabetes Atlas. 11th edition. Brussels 2025.
Important note:
The information in this encyclopedia article is intended solely for general and non-binding information. They do not replace medical advice, diagnosis or therapy. If you have any health questions or complaints, please always consult a doctor or qualified healthcare professional. The content was created with the greatest possible care, but errors cannot be completely ruled out.
Last updated: February 26, 2026
