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Young People to Use CGM to Improve Diabetes

By Jeemin Kwon

The new CITY trial will enroll 200 young adults with type 1 diabetes to study the impact of CGM use on diabetes, especially when A1c levels are high.

Clinical Trials Identifier: NCT03263494

Trial name: CGM Intervention in Teens and Young Adults With Type 1 Diabetes (T1D) (CITY)

Diabetes type: Type 1 diabetes

What the trial is testing: The trial is testing the impact of continuous glucose monitoring (CGM) use – specifically with a Dexcom G5 CGM – in teens and young adults who are not meeting their diabetes management goals. Because CGM collects real-time glucose information and alarms for highs/lows, it allows users to be more proactive, to spend more time-in-range (70-180 mg/dl), and to (usually) reduce their A1c while decreasing hypoglycemia. Many CGM users also learn a lot about how different factors affect their blood sugar levels, especially food and exercise. (Read how Adam uses his CGM data to approach his time-in-range goals here.)

What the trial is measuring: The primary result will be the change in each trial participant’s A1c after six months. In addition, researchers will be looking at multiple secondary results, including time-in-range, average blood glucose level, blood glucose variability (measured by the coefficient of variation in CGM readings), hypoglycemia (low blood sugar below 54 mg/dl), as well as participant-reported information from questionnaires about CGM use, attitudes towards diabetes technology, and more.

Why is this new/important? In the US T1D Exchange registry, teenagers and young adults with type 1 diabetes have the highest A1c levels and some of the lowest rates of CGM use of anyone in the system. This trial could help further demonstrate the value of CGM in this high-need population. In addition, the historic JDRF CGM trial, which used older CGM devices and was published in 2008, showed the benefits of CGM in individuals 25 years and older; in younger age groups (8-24 years), the older-generation devices had low rates of wear in the trial, and did not show a benefit in this group. This trial using the more modern Dexcom G5 could provide important evidence that CGM does benefit the adolescent and young adult age groups. Assuming the results are positive, CITY could encourage more prescribers to recommend CGM in adolescents and young adults, and ideally drive insurance companies to offer more favorable CGM coverage in these younger age groups.

Trial length: Six months

Trial locations: This study will enroll 200 people with type 1 diabetes at 14 locations across the US, including Los Angeles, CA; Palo Alto, CA; New Haven, CT; Boston, MA; New York, NY; Syracuse, NY; Philadelphia, PA; Houston, TX; as well as sites in Colorado, Idaho, Minnesota, Missouri, North Carolina, and Tennessee. Click here for the full list, including to find out which sites have already begun recruiting participants.

Do you qualify?

Select criteria include:

  • Ages 14 to <25 years

  • Diagnosed with type 1 diabetes for longer than one year

  • Taking 0.4 units/kg of insulin or more per day

  • A1c 7.5% to <11%

  • Already checking blood sugar levels at least twice a day with a blood glucose monitor

  • Have not used a real-time CGM as part of diabetes management in the past 3 months

  • Have not started using a non-insulin diabetes drug in the past three months and do not plans to start one in the next six months

Where to get more information: For more information about this trial or about specific trial locations, please contact

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