Evidence-Based Practice: Continuous glucose monitoring (CGM) is clinically valuable in reducing risks of hypoglycemia and hyperglycemia, improving glycemic variability, and im- proving the quality of life for people with type 1 and type 2 diabetes 4 . CGM should be offered to everyone with diabetes who uses multiple daily insulin injections. Depending on the brand of CGM, it may have the ability to integrate with an in- sulin pump. Self-Assessment Quiz Question #1 What is the added value of continuous glucose monitoring (CGM) over fingerstick blood glucose monitoring (BGM)? a. CGM is less expense, since there is no need to purchase a lancet or test strips to use with a glucometer. b. CGMs provide a direct measure of glucose in the plasma. c. CGMs provide a more complete picture of how blood glucose levels change over time. d. CGMs tell why blood glucose increases or decreases. nect does not use a receiver, whereas the other three monitors do. Three of the monitors have an iPhone and an Android app, while the Libre 2 does not. The Dexcom G6 and Guardian Con- nect CGMs provide real-time readings, while the Libre models re- quire the user to scan the sensor to get a reading. For most of the current CGMs, the sensor is worn on either the abdomen or the upper arm depending on the monitor. And only some monitors are designed to share results with family/friends, which may be an important consideration if the person with diabetes is a child or has cognitive impairment. The monitoring sensor should be replaced every 7 to 14 days depending on the CGM device.
CGM works by utilizing a tiny sensor inserted under the skin via an applicator and secured with an adhesive patch. The sensor is inserted into the abdomen or back of the arm. Attached to the sensor is a glucose-oxidase platinum electrode that measures the glucose concentration found in interstitial fluid throughout the day and night. A transmitter connects to the sensor and sends real-time glucose readings wirelessly to a receiver to view the in- formation. Data are viewed on the receiver and can be down- loaded for reports. The technology used in CGM systems, and most home blood glucose meters, relies on measuring an elec- trochemical signal generated from the reaction of an enzyme, glucose-oxidase, with glucose. CGM measures blood glucose continuously, as often as every 5 minutes, with close to 300 measurements per day. With so many glucose measurements throughout the day, CGM provides trend information about the direction and rate of changing glucose con- centrations. Furthermore, many CGM devices sound alarms to warn of low or high, or falling or rising glucose levels. In addition, a CGM can connect to an insulin pump that automatically adjusts or suspends insulin delivery in response to glycemic trends 13 . Selecting a CGM device There are currently (as of September 2022) four continuous glu- cose monitors available for people with diabetes who are not us- ing an insulin pump. Some of the insulin pumps have a specific CGM to be used in tandem with the specific insulin pump (e.g., the Tandem insulin pump integrates with a Decom G6 CGM, and the Medtronic insulin pump integrates with a Guardian 3 CGM). People not on an insulin pump can choose a Dexcom G6, a Li- bre 14, a Libre 2, or a Guardian Connect. Insurance companies vary in their requirements for coverage and the brands they cover. People also have the option to self-pay. The pumps are similar but vary in some of their features. For example, the Guardian Con- Personal CGM devices Personal CGM devices are purchased for personal use to monitor blood glucose levels and help guide decision-making about food intake, physical activity, and medication use. In addition, CGM de- vices keep track of blood glucose data by sending information to Real-time versus intermittently scanned CGM devices Two types of personal CGM devices are available: real-time CGM (rtCGM) and intermittently scanned CGM (isCGM). The rtCGM devices indirectly measure blood glucose levels every 5 minutes and send glucose data automatically to a receiver or smartphone. The 2022 Standards of Medical Care from the ADA recommend use of an rtCGM device for people with type 1 diabetes who do not meet individualized glycemic targets and experience hypogly- cemia unawareness 4 . These rtCGM devices also can sound alerts and alarms in response to rising or falling blood glucose levels. Some patients get frustrated with the frequent alarms if they ex- perience significant variability with their blood glucose levels 16 . If the alarms are too frequent, some wearers feel like their diabetes is controlling their lives. CGMs can be customized by setting the alarms at different glucose levels to limit alarms during work activ- ities or school. Use of an isCGM device to retrieve blood glucose data, which requires manually scanning the sensor 16 , is another approach to limiting frequent alarms. The rtCGM devices provide real-time feedback to patients. There are select times, however, when a provider may choose to blind Interpreting CGM data CGM systems are based off rtCGM or isCGM, which measure blood glucose levels in interstitial fluid. CGM systems also pro - vide insight into direction, magnitude, duration, frequency, and rate of change (ROC) by displaying the information as a trend arrow on the sensor next to the actual blood glucose value. Such a feature is vital in helping patients anticipate future blood glu- cose levels. In addition, the visual representation of information in the form of arrows enables patients to take action to adjust their blood glucose levels promptly 15,17 .
a receiver or smart device. The use of CGM devices identifies the need to respond to blood glucose variability and increase their confidence in blood glucose management for many 15 .
the wearer to the data and have the person use a professional CGM from the office. This can be useful when the person is not changing their behavior based on the blood glucose readings; instead, the data are being collected so that the healthcare pro- vider can look at patterns then make recommendations. Having the individual wear a professional CGM from the office, may be indicated if someone’s insurance will not cover the cost of a per- sonal CGM on a regular basis. The professional CGM can be used intermittently to help with decision making regarding therapy rec- ommendations. The isCGM devices require the person to pass or swipe a scan- ner over the sensor/transmitter to receive blood glucose data. First-generation isCGM devices did not include alarms or alerts for high or low blood glucose readings. Newer CGM devices now offer added safeguards and alerts. isCGM devices may be helpful to patients who have a difficult time performing BGM with a glu - cometer and fingersticks as recommended because of dexterity issues or other related problems 16 . Each CGM system has a different representation of trend arrows but generally represents blood glucose levels changing at a rate of <1 mg/dL per minute (horizontal arrow) to up to >2–3 mg/ dL per minute (single or double vertical arrows pointing upward), with the opposite for declining blood glucose levels (horizontal arrows pointing down). However, with no standardized guidelines or protocols for interpreting blood glucose values provided by trend arrows, healthcare providers need to make recommenda-
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