Continuous Glucose Monitoring in Type 2 Diabetes

Continuous glucose monitors (CGMs) are increasingly used in diabetes care. They provide a way to measure glucose levels that many find convenient. A CGM is a small device that is worn on the body, most commonly on the back of the upper arm. There are various configurations and models of CGMs, but the most common models in use today transmit a glucose reading regularly to an app on a smart phone. CGMs were first used by people utilizing multiple daily injections of insulin but are increasingly being used by people with diabetes who do not use insulin and even by some people without diabetes.

Prior to CGMs becoming widespread, people with diabetes would typically use a glucometer to check their blood glucose. A glucometer requires a finger prick each time a glucose measurement is needed. It measures the glucose level in the blood.  Instead of measuring blood glucose, a CGM measures the glucose present in the interstitial fluid, which is the fluid between the cells just under the skin.  CGM users should be aware that because the CGM measurement is derived from interstitial fluid, it will lag behind the blood glucose reading by around 5 to 15 minutes.  Another caveat is that, as with any technology, there can be irregularities or malfunctions. So, if the measurements that a CGM is giving do not correlate with symptoms or with the context, one should measure blood glucose with a glucometer to corroborate the findings.

When insulin is used, particularly if the dose is adjusted based on blood glucose readings, the potential utility of continuous glucose monitoring is evident. However, it has also been observed that people with diabetes who are not prescribed insulin can often improve their glycemic control by using a CGM. This is largely due to lifestyle changes that an individual chooses to make based on their blood glucose numbers. For example, an individual may note that certain foods cause higher glucose spikes than others and so choose to change how they consume those foods. They may also notice the effect of exercise on blood glucose and so make changes in that regard.   

A randomized controlled trial (RCT) was published earlier this year in the journal Diabetes Technology and Therapeutics in an article entitled “A Randomized Controlled Trial Using Continuous Glucose Monitoring to Guide Food Choices and Diabetes Self-Care in People with Type 2 Diabetes not Taking Insulin.”  In this trial, 72 adults with type 2 diabetes were randomized into one of two groups. One group used a CGM while the other group used a CGM plus a food logging app. The primary endpoint was time with glucose over 180mg/dL as measured by the CGM. Glycated hemoglobin (HbA1C) and bodyweight were also measured. They found both groups decreased the amount of time spent with glucose over 180mg/dL, decreased HbA1C and lost weight.  For both groups, the time with glucose in the target range (70-180mg/dL) increased from 46% at baseline to 72% at 6 months.

A meta-analysis was published this year in the journal Diabetes, Obesity and Metabolism entitled “Continuous glucose monitoring in noninsulin-treated type 2 diabetes: A critical review of reported trials with an updated systematic review and meta-analysis of randomised controlled trials.”  The authors conducted a meta-analysis of 8 randomized controlled trials that included 541 individuals with type 2 diabetes who were not using insulin. They found that CGM use was associated with lower HbA1C, increased time with glucose in the target range and decreased time with glucose above the target range.

While once used primarily by people using multiple daily injections of insulin, CGMs have also shown benefit for people with diabetes who are not using insulin. This benefit is likely derived from making beneficial lifestyle changes based on the glucose data.

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