What is CGM and BGM?
CGM (Continuous Glucose Monitoring) continuously measures glucose levels in interstitial fluid through a subcutaneous sensor, providing real-time data like a "movie" of glucose changes, while BGM (Blood Glucose Monitoring) measures capillary blood glucose at discrete time points using fingerstick test strips, providing snapshots of glucose values. 1
Continuous Glucose Monitoring (CGM)
Core Technology
- CGM measures glucose concentrations in subcutaneous interstitial fluid through an implanted glucose sensor, typically using electrochemical principles where glucose oxidase enzyme interacts with glucose to generate electrical signals that are converted to glucose readings 1
- The system consists of a glucose sensor, data transmitter, data receiver/display, sensor introducer device, and analysis software 1
- Sensors are inserted subcutaneously and worn externally by the user, though implantable CGM devices are also becoming available 1
Types of CGM Systems
Real-Time CGM (RT-CGM):
- Data is transmitted continuously to a receiver, allowing alerts and alarms for high and low glucose values 1
- Provides immediate blood glucose readings with glucose alarms and predictive alerts, facilitating immediate glucose adjustment 1
- Users can see glucose data as it is being collected 1
Retrospective (Blinded) CGM:
- Equivalent to "Holter"-style glucose monitoring where results are obtained after completion of monitoring 1
- Patients are "blinded" to the data and cannot obtain results until the end of the monitoring period 1
- More objectively records glucose patterns and reflects the actual effect of intervention treatment 1
Intermittently Scanned CGM (isCGM):
- Also known as "flash" glucose monitoring (FreeStyle Libre), where interstitial glucose levels are measured continuously but data are not transmitted continuously from the sensor 1
- Results are available only when the sensor is scanned with a reading device 1
- Full 24-hour data can be captured if the sensor is scanned at least every 8 hours 1
- Lower daily costs and no calibration required, but alarms are not provided for high and low glucose values 1
Key Characteristics
- Reflects continuous glycemic changes like a "movie" rather than snapshots 1
- Provides continuous glycemic data, fully reflecting glycemic changes with diet, drugs, exercise, etc. 1
- Reflects the direction or speed of glucose changes and helps users understand overall trends and individualized features of glucose changes 1
- Allows detection of occult hyperglycemia and hypoglycemia that cannot be detected by traditional blood glucose monitoring methods 1
Blood Glucose Monitoring (BGM)
Core Technology
- BGM measures capillary blood glucose using disposable test strips and a glucose meter 1
- Uses test strips and a pricker, mostly at the fingertip or other sites 1
- Also referred to as self-monitoring of blood glucose (SMBG) 1
Key Characteristics
- Reflects glucose value at a certain time point, like a "snapshot" 1
- Provides sporadic glycemic data, partially reflecting glycemic changes with diet, drugs, exercise, etc. 1
- Retrospective analysis based on the output of sporadic glucose values 1
- Some glucose analyzers have data storage function, and glycemic data can be uploaded to a computer through software 1
Critical Differences Between CGM and BGM
Measurement Site
- CGM measures glucose concentration in subcutaneous interstitial fluid 1
- BGM measures capillary blood glucose 1
Data Continuity
- CGM provides continuous 24-hour monitoring through implantation of a glucose sensor 1
- BGM provides glucose detection at discrete time points using disposable test strips 1
Clinical Utility
- CGM provides continuous and comprehensive all-day glucose profiles, allowing understanding of trends in blood glucose fluctuations 1
- BGM provides intermittent data points that require interpretation to understand patterns 1
Important Clinical Caveats
CGM Limitations
- CGM is not suitable for patients on peritoneal dialysis due to potential interference from icodextrin, a component of peritoneal dialysis solutions 2, 3
- High-dose acetaminophen (>4 g per day) may interfere with glucose readings in some CGM systems 2
- Salicylic acid and ascorbic acid can affect sensor accuracy by reacting with the sensor's electrode 2
- CGM should be avoided during MRI, and conventional X-ray imaging and CT scanning should be avoided with some devices 1