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Continuous Glucose Monitor

Continuous Glucose Monitoring (CGM) use can improve blood glucose control in individuals of all ages with type 1, type 2, and gestational diabetes. They help reduce HbA1C and prevent hyper- and hypoglycemia.

Nutrition/Endocrinology

InShort

continuous glucose monitor

AKA Glucose monitoring

CGM


A continuous glucose monitor (CGM) is a device that tracks glucose levels using a sensor inserted under the skin. The sensor measures glucose levels in the interstitial fluid every 1 to 5 minutes. The sensor is connected to a small transmitter that wirelessly sends data to a receiver such as the monitor that comes with the CGM, a cell phone, or smart watch. Some CGMs trigger an alarm if glucose drops below or rises above a set level. Tracking glucose levels in real time allows informed decisions about food choices, physical activity, and medication.


Indications:

Individuals with diabetes. CGMs are often but not always used in conjunction with an insulin pump.


CGMs are now being marketed to individuals with prediabetes, athletes, individuals working to manage their weight, and others concerned with fluctuations in blood glucose.


Contraindications:

CGM values should not replace venous glucose testing when treating hyper- or hypoglycemia because the readings are less accurate at extremes of blood glucose and during periods of rapid change in blood glucose levels.

The sensor and/or adhesive may cause contact dermatitis.


Pearls to Know:

  • CGM use can improve blood glucose control in individuals of all ages with type 1, type 2, and gestational diabetes. They help reduce HbA1C and prevent hyper- and hypoglycemia.

  • CGM values may lag 5–15 minutes behind blood glucose levels because of the time it takes for blood glucose to equilibrate with interstitial fluid glucose.

  • CGMs can eliminate the need for finger stick glucose measurements, but people with diabetes should also have access to a blood glucose monitor as a back up.

  • CGMs are available with a prescription for individuals with diabetes. CGMs are also available without a prescription for those interested in monitoring how their blood glucose responds to diet, exercise, stress, and other factors. These devices can be costly if not covered by insurance or if obtained without a prescription.

  • CGMs are easy to use, particularly for tech savvy individuals. Guidance on sensor insertion and use can be obtained from package insert instructions, online instructional videos, or by training provided and billed as part of diabetes self-management training.

  • In the inpatient setting and during outpatient procedures CGM use should be continued once the patient’s competency has been established.

  • Sleeping position can put pressure on the CGM sensor, leading to false low glucose values (and less often to high values).

  • CGM values may not be accurate during or for up to 90 minutes after exercise.


 

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References

ElSayed NA, Aleppo G, Aroda VR, et al., American Diabetes Association.7. Diabetes technology: Standards of care in diabetes—2023. Diabetes Care. 2022;46(Suppl. 1): S111–S127. doi:10.2337/dc23-s007.

Lind M, Ólafsdóttir A F, Hirsch IB, et al. Sustained intensive treatment and long-term effects on HbA1c reduction (SILVER Study) by CGM in people with type 1 diabetes treated with MDI. Diabetes Care. 2021;44(1):141–149. doi:10.2337/dc20-1468.

Avari P, Reddy M, Oliver N. Is it possible to constantly and accurately monitor blood sugar levels, in people with type 1 diabetes, with a discrete device (non-invasive or invasive)? Diabet Med. 2020;37(4):532-544. doi:10.1111/dme.13942.

Mensh BD, Wisniewski NA, Neil BM, Burnett DR. Susceptibility of interstitial continuous glucose monitor performance to sleeping position. J Diabetes Sci Technol. 2013; 7(4):863-870. doi:10.1177/193229681300700408.

Da Prato G, Pasquini S, Rinaldi E, et al. Accuracy of CGM systems during continuous and interval exercise in adults with type 1 diabetes. J Diabetes Sci Technol. 2022;16(6):1436-1443. doi:10.1177/19322968211023522.

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