A1C has been used to estimate 3-month glycemic control in patients with diabetes. However, A1C monitoring alone does not provide insight into daily glycemic variation, which is valuable in clinical management because tight glycemic control (defined as A1C < 7.0%) has been shown to reduce the risk of microvascular complications. Prior to the approval of glucagon-like peptide-1 receptor agonists and sodium-glucose co-transporter 2 inhibitors by the US Food and Drug Administration for the treatment of type 2 diabetes (T2D), reduction in the risk of macrovascular complications (aside from nonfatal myocardial infarction) was more difficult to achieve than it is now; some patients had a worse outcome with overly aggressive glycemic control.1
Previously, the use of a continuous glucose monitor (CGM) was limited to patients with type 1 diabetes who required basal and bolus insulin. However, technological advances have led to more patient-friendly and affordable devices, making CGMs more available. As such, the American Diabetes Association (ADA), in its 2022 Standards of Medical Care in Diabetes, recommends that clinicians offer continuous glucose monitoring to adults with T2D who require multiple daily injections, and based on a given patient’s ability, preferences, and needs.2
In this article, we discuss, first, the intricacies of CGMs and, second, what the evidence says about their use so that physicians can confidently recommend, and educate patients on, effective utilization of CGMs to obtain an individualized target of glycemic control.
Continuous glucose monitoring: A glossary
CGMs are characterized by who possesses the device and how data are recorded. This review is not about professional CGMs, which are owned by the health care provider and consist of a sensor that is applied in the clinic and returned to clinic for downloading of data1; rather, we focus on the novel category of nonprofessional, or personal, CGMs.
Three words to remember. Every CGM has 3 common components:
- The reader (also known as a receiver) is a handheld device that allows a patient to scan a sensor (see definition below) and instantaneously collect a glucose reading. The patient can use a standalone reader; a smartphone or other smart device with an associated app that serves as a reader; or both.
- A sensor is inserted subcutaneously to measure interstitial glucose. The lifespan of a sensor is 10 to 14 days.
- A transmitter relays information from the sensor to the reader.
The technology behind a CGM
CGM sensors measure interstitial glucose by means of a chemical reaction involving glucose oxidase and an oxidation-reduction cofactor, measuring the generation of hydrogen peroxide.3 Interstitial glucose readings lag behind plasma blood glucose readings by 2 to 21 minutes.4,5 Although this lag time is often not clinically significant, situations such as aerobic exercise and a rapidly changing glucose level might warrant confirmation by means of fingerstick measurement.5 It is common for CGM readings to vary slightly from venipuncture or fingerstick glucose readings.
What CGMs are availableto your patients?
Intermittently scanned CGMs (isCGMs) measure the glucose level continuously; the patient must scan a sensor to display and record the glucose level.6 Prolonged periods without scanning result in gaps in glycemic data.7,8
Continue to: Two isCGM systems...