A Guide to CGMs, with Certified Diabetes Educator Michael-John L. Smith

An Overview of CGMs, with Certified Diabetes Educator Michael-John L. Smith

How does a CGM work? What do you need to know about type 1 diabetes and pregnancy? What are some driving safety tips for people living with type 1 diabetes? We’re answering these questions and more in a new Q&A series featuring certified diabetes educators (CDEs).

In this piece, we spoke with Michael-John L. Smith, RN, BSN, CCDTC, is the Clinical Leader at Nationwide Children’s Hospital in Columbus, Ohio. He has also lived with type 1 diabetes for over 27 years. During Smith’s time at Nationwide Children’s Hospital, he has implemented several technology changes that have increased work efficiency and patient satisfaction. Smith and his team serve as an active part in the T1D Exchange Quality Improvement Collaborative. 

What is a CGM?

CGM stands for “continuous glucose monitor”. This is a small device worn by a person for a certain length of time to capture the up and down trends of interstitial (fluid between the cells) glucose readings. 

What are the parts of a CGM and what are they responsible for?

 Different models have varying parts of the CGM. The majority of CGM systems have the following parts:

 Transmitter: A small electronic device that wirelessly sends CGM readings to the receiver. Depending on the CGM model, the transmitter can be reused, but will need to be replaced after 3 months, 6 months, or after each use. One brand’s transmitter is USB rechargeable, which allows the wearer to use it multiple times without having to replace it.

Receiver: A device usually kept on the body. This device collects and displays the glucose readings for the wearer or caregiver to view. Many companies are now switching to using a personal cellular phone to capture CGM readings via Bluetooth technology. 

Sensor: The part that is inserted into the body and “reads” the interstitial glucose readings via biochemistry. It then sends readings to the transmitter. For most CGM systems, the sensor consists of a thin filament (about as thin as an eyelash) that is inserted in the fatty part of the wearers tissue – usually the arms, stomach, or hip. Some CGMs are approved for use at one of these sites, while others are approved for multiple sites. One CGM system has an implantable sensor for wearing under the skin, which must be replaced every 90 days and requires a simple, in-clinic procedure. 

How do people with type 1 diabetes use a CGM?

 People with type 1 diabetes utilize CGM readings to interpret trends in blood sugar management so that, with their health team, individuals can make informed decisions about their care. CGM is also a great tool that allows a person with type 1 diabetes to predict and prevent when a low or high glucose reading may occur.

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What are the pros and cons of CGM technology?

 The pros and cons vary from person to person. 

Some of the pros include:

  • No fingersticks to calibrate for some CGMs
  • The ability to make dosing decisions based on CGM readings 
  • For parents, the ability to see their child’s glucose readings throughout the day and night, and receive an alarm when a low glucose reading occurs

Cons can include:

  • Having another “device” attached to the body
  • “Alarm fatigue,” when alarms go off at inopportune times 
  • Cost, as the cost for these systems are variable and depend on insurance coverage

What CGMs are currently on the market?

There are several on the market, from stand-alone systems to models that are integrated with pump therapy. Some of these include:

  • Dexcom – a stand-alone system that can be integrated with pump companies like Tandem and Insulet
  • Medtronic – which makes a stand-alone system that can also be integrated with Medtronic pumps
  • Abbott – manufacturer of the Freestyle Libre
  • Senseonics – the maker of the implantable sensor, Eversense

Is there evidence that CGM use can improve blood sugar management?

Yes, there is data to show slight improvement of blood sugar management with the use of CGMs. With the increase in usage of CGMs, we are starting to use Time-in-Range (TIR) as a better indicator for blood sugar management vs. the traditional hemoglobin A1c (HbA1c) level. 

The T1D Exchange Quality Improvement Collaborative has been collecting data from participating sites, including Nationwide Children’s Hospital, on CGM usage and HbA1c level. We hope to further interpret the data and use these findings to help those with diabetes have the best outcomes.    

What are some recent improvements in CGM technology that interest you as a health care provider?

CGMs allow health care providers to view the glucose readings that we wouldn’t normally see with finger sticks. This way, we can see “the bigger picture,” viewing trends for days, weeks, and months, and make more informed decisions.

How does a CGM fit into artificial pancreas or closed-loop insulin pump technology?

CGM usage is what makes closed-looped pump systems function. The feedback from the CGM allows the pump to adjust based on those CGM readings. The pump may give a little extra to bring the glucose down but it can also give a little less to allow glucose to rise.  

What is the difference between a CGM and an intermittently scanned CGM (isCGM)?

The Freestyle Libre is an isCGM, which must be “waved” over the sensor to display the glucose data. Other CGMs will automatically display the readings on the receiver about every 5 minutes. This is a personal preference option of simply waving the receiver over a sensor to get a displayed reading or the data being automatically displayed on the receiver. 

What might someone with insurance expect to pay for a CGM? What if that person had to pay out of pocket?

Many of the costs for these products are driven by insurance and their contracted rates with either manufacturers or a DME (durable medical equipment) company. Some CGMs are now covered under a patient’s pharmacy benefits program as opposed to their medical benefits. I suggest checking with your insurance on what the associated costs of your preferred CGM would be and ask if it’s covered under pharmacy or medical, and if you must use a DME company.

Make sure the insurance is contracted with a DME that supplies your preferred CGM. If you’re having trouble, ask your diabetes health care team or the manufacturer for common DME companies or pharmacies in your area. If you are considering an implantable sensor, make sure to inquire as to what the associated costs will be for insertion.

Before starting any CGM, do your research, ask questions, and be informed.

Interview compiled by Shahd Husein

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