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Type 1 Diabetes MellitusPhase 3CITYNCT03263494

CGM Intervention in Teens and Young Adults With Type 1 Diabetes (T1D)

A Phase 3 study testing Continuous Glucose Monitor (CGM) in people with Type 1 Diabetes Mellitus, run by Jaeb Center for Health Research at 14 sites in United States.

Completed

Finished. The study has ended and is not enrolling. Results may be posted on the official record.

Official record
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Trial summary

Adolescents and young adults with T1D and poor glycemic control (age 14-< 25 years, T1D duration >12 months, HbA1c 7.5-<11.0%, using an insulin pump or MDI)) will be randomly assigned to either CGM or BGM. Sample size will be 150. The primary outcome assessment will be HbA1c after 6 months. Read more about this study

Who is it for?
Ages 14 to 24 years
Conditions the study is for
Type 1 Diabetes Mellitus
What is being tested?
Continuous Glucose Monitor (CGM)
Type of treatment
Medical device
Could I receive a placebo?
No, everyone receives an active treatment
How many people
153 participants
Where
14 sitesUnited States
Study dates
25 Jan 2018to 7 Nov 2019
Phase
Phase 3
Are there results?
Yes, posted in the registrySummary in the doctors' view

Key requirements

Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.

  • Ages 14 to 24 years
  • All sexes
  • No healthy volunteers
  • Child, Adult

Who may be able to join

  • Clinical diagnosis of T1D, with either age of T1D diagnosis < 10 years of age OR a history of positive T1D related antibodies in the medical record
  • Age 14-<25 years
  • Diabetes duration ≥ 1 year
  • Total daily insulin requirement ≥ 0.4 units/kg/day
  • HbA1c 7.5% to <11.0% (Point of care device or local lab measured as part of study at screening visit)
  • Insulin regimen involves a consistent modality of insulin administration with either use of an insulin pump or at least 3 multiple daily injections of basal and bolus (meal time) analogue insulin. Insulin pump must not have been started within 3 months of consent with no plans to change regimens in the next 6 months
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  • Perform at least 2 blood glucose meter checks per day from self-report at screening and an average of at least 2 checks per day from meter download during blinded CGM run in
  • Blinded CGM must be used a minimum of 200 hours (equivalent to 8.3 days) with an average of 1.8 calibrations per day during the blinded CGM screening period.
  • Participant comprehends written and spoken English
  • Participant understands the study protocol and agrees to it (if applicable)

Who cannot join

  • Use of unblinded personal CGM and/or flash CGM, outside of a research study, as part of real-time diabetes management in the last 3 months
  • Unable to use CGM device for minimum number of hours during blinded pre-randomization period or skin reaction from adhesive that would preclude participation in the randomized trial
  • Started on non-insulin medication for blood glucose control within the past 3 months or plans to begin within the next 6 months
  • The presence of a significant medical disorder that in the judgment of the investigator will affect the wearing of the sensors (such as a skin condition), or the completion of any aspect of the protocol.
  • More than 1 episode of DKA in the past 6 months as defined in the adverse events chapter.
  • The presence of any of the following diseases:
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  • Asthma or any condition present in the last 6 months where treatment is a systemic or daily inhaled corticosteroid (Intermittent treatment with inhaled corticosteroids does not exclude subjects from enrollment)
  • Cystic fibrosis
  • Addison's disease (Adequately treated thyroid disease and celiac disease do not exclude subjects from enrollment)
  • Inpatient psychiatric treatment in the past 6 months or daily intensive outpatient psychiatric day treatment in the past 3 months.
  • Pregnant (positive test confirmed at screening) or planning to become pregnant in the next 12 months.
  • Need for use of acetaminophen or acetaminophen-containing products on a regular basis during the 6 months of the trial
  • Participation in a diabetes related intervention study in the past 6 weeks.
  • Any medical, psychological or social situation where per investigator discretion it may be difficult for participant to participate fully in the intervention
  • Any condition, per investigator assessment, that could impact reliability of the A1C measurement, such as (but not limited to) hemoglobinopathy, hemolytic anemia, chronic liver disease; chronic GI blood loss, red blood cell transfusion or erythropoietin administration within 3 months prior to screening

Trial locations and contacts

14 sites in 1 country.

14 sites in 1 country

United States14 sites

  • Barbara Davis Center--University of Colorado

    Aurora, Colorado, 80045

  • Joslin Diabetes Center

    Boston, Massachusetts, 02215

  • University of North Carolina

    Chapel Hill, North Carolina, 27713

  • Baylor College of Medicine

    Houston, Texas, 77030

  • Rocky Mountain Diabetes & Osteoporosis Center

    Idaho Falls, Idaho, 83404

  • Children's Mercy Hospital

    Kansas City, Missouri, 64111

  • Children's Hospital Los Angeles

    Los Angeles, California, 90027

  • Vanderbilt University

    Nashville, Tennessee, 37212

  • Yale University

    New Haven, Connecticut, 06511

  • Naomi Berrie Diabetes Center at Columbia University

    New York, New York, 10032

  • Stanford University

    Palo Alto, California, 94304

  • Children's Hospital of Philadelphia

    Philadelphia, Pennsylvania, 19104

  • IDC at Park Nicollet

    Saint Louis Park, Minnesota, 55416

  • SUNY Upstate Medical University

    Syracuse, New York, 13210

Other trials in United States

About this study

Official title: CGM Intervention in Teens and Young Adults With T1D (CITY): A Randomized Clinical Trial to Assess the Efficacy and Safety of Continuous Glucose Monitoring in Young Adults 14-<25 With Type 1 Diabetes

Adolescents and young adults with T1D and poor glycemic control (age 14-< 25 years, T1D duration >12 months, HbA1c 7.5-<11.0%, using an insulin pump or MDI)) will be randomly assigned to either CGM or BGM. Sample size will be 150. The primary outcome assessment will be HbA1c after 6 months. Secondary outcomes will include HbA1c, CGM metrics (control group will wear blinded CGM at 13 and 24 weeks), and quality of life measures. The randomized trial will be followed by a 6-month extension study during which the RCT control group will initiate CGM and the RCT CGM group will continue CGM.

Being tested
Continuous Glucose Monitor (CGM)
Medical subject headings
Diabetes Mellitus, Type 1

What participants receive

What participants receive. In a randomised study each person is assigned to one group by chance.

  • Continuous Glucose Monitor (CGM)Device

    Participants randomized to the CGM Group will receive a Dexcom CGM device and be instructed on how to utilize the CGM data in real time for diabetes management.

Study groups in NCT03263494
Study groupRoleWhat they receive
CGMActive comparatorNot described
Receives: Device: Continuous Glucose Monitor (CGM)
BGMNo interventionNot described

What is being measured

The primary outcome is the main question the study is designed to answer.

  1. Change in HbA1c From Baseline to 26 Weeks Adjusted for Baseline

    Measured: 6 months

Secondary outcomes (20)

  1. % With HbA1c <7.0%

    Measured: 6 months

  2. % With HbA1c <7.5%

    Measured: 6 months

  3. % With Relative Reduction ≥ 10%

    Measured: 6 months

  4. % With Absolute Reduction ≥ 0.5%

    Measured: 6 months

  5. % With Absolute Reduction ≥ 1%

    Measured: 6 months

  6. % With Absolute Reduction ≥ 0.5% or HbA1c < 7.0%

    Measured: 6 months

  7. CGM % Time in Range 70-180 mg/dl

    Measured: 6 months

  8. CGM Mean Glucose

    Measured: 6 months

  9. CGM Glucose Variability Measured by Coefficient of Variation

    Measured: 6 months

  10. CGM % Time > 180 mg/dl

    Measured: 6 months

  11. CGM % Time > 300 mg/dl

    Measured: 6 months

  12. CGM % Time < 54 mg/dl

    Measured: 6 months

  13. CGM % Time < 70 mg/dl

    Measured: 6 months

  14. Rate of CGM Measured Hypoglycemic Episodes (Using <54 mg/dL)

    Measured: 6 months

  15. CGM Self Efficacy Questionnaire Score

    Questionnaire containing 15 questions with possible responses 0-6. Total score is calculated by taking the mean of the non-missing responses. Then multiply by 100 and divide by 6 to put on the scale 0-100. Higher total score indicates higher perceived ability.

    Measured: 6 months

  16. Problem Areas in Diabetes (PAID) Questionnaire Score

    Survey containing 20 questions with possible responses 0-5. Total score is calculated by taking the mean of the non-missing items and multiplying by 20 to put on the scale 0-100. A higher total score indicates more of a problem.

    Measured: 6 months

  17. Glucose Monitoring Satisfaction Questionnaire Score

    Survey containing 15 questions. Total score ranges from 0-100. A higher total score indicates more satisfaction with their current glucose monitor.

    Measured: 6 months

  18. Hypoglycemia Confidence Questionnaire Score

    Survey containing 9 questions with possible responses 0-4. Total score is calculated by taking the mean of non-missing responses and multiplying by 25 to put on the scale 0-100. Higher total score indicates more confidence.

    Measured: 6 months

  19. Diabetes Technology Attitudes Questionnaire Score

    Survey containing 5 questions with possible responses 0-4. Total score is calculated by taking the mean of non-missing responses and multiplying by 25 to put on the scale 0-100. Higher total score indicates a more positive attitude towards diabetes technology.

    Measured: 6 months

  20. Pittsburgh Sleep Quality Index

    Survey containing 19 questions. Total score ranges from 0-21. A lower score indicates a healthier sleep quality.

    Measured: 6 months

Timeline

From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.

  1. First posted28 Aug 2017
  2. Study start25 Jan 2018
  3. Primary completion8 May 2019
  4. Study completion7 Nov 2019

Resources

More details

For doctors and researchers: how the study is designed, who runs it, and its registry IDs.

Study design
Study type
Interventional
Phase
Phase 3
Primary purpose
Treatment
Allocation
Randomised
Intervention model
Parallel groups
Masking
None (open label)
Enrolment
153 participants (actual)
IDs, dates and publications
ClinicalTrials.gov ID
NCT03263494
Sponsor's protocol ID
CITY
Acronym
CITY
Status last verified
Jul 2026
First submitted
24 Aug 2017
Last updated
9 Jul 2026
Data monitoring committee
Yes
FDA-regulated drug
No
FDA-regulated device
Yes
Individual data sharing
No

Publications

  • Bilionis I, Berrios RC, de Arriba Munoz A, Fernandez-Luque L, Castillo C. A framework for assessing algorithmic discrimination risks in training data: a case of pediatric type 1 diabetes. JAMIA Open. 2026 Jul 14;9(4):ooag125. doi: 10.1093/jamiaopen/ooag125. eCollection 2026 Aug.

    PubMed 42459945

  • Miller KM, Bauza C, Kanapka LG, Clements MA, DeSalvo DJ, Hood K, Messer LH, Sherr J, Bergamo K, Criego A, Freiner E, Lyons SK, Monzavi R, Moore W, Prahalad P, Simmons JH, Sulik M, Wadwa RP, Weinstock RS, Willi SM, Williams K, Laffel LM; CITY Study Group. Continuous Glucose Monitoring Provides Durable Glycemic Benefit in Adolescents and Young Adults with Type 1 Diabetes: 12-Month Follow-Up Results. Pediatr Diabetes. 2023 Oct 26;2023:6718115. doi: 10.1155/2023/6718115. eCollection 2023.

    PubMed 40303270

  • Laffel LM, Kanapka LG, Beck RW, Bergamo K, Clements MA, Criego A, DeSalvo DJ, Goland R, Hood K, Liljenquist D, Messer LH, Monzavi R, Mouse TJ, Prahalad P, Sherr J, Simmons JH, Wadwa RP, Weinstock RS, Willi SM, Miller KM; CGM Intervention in Teens and Young Adults with T1D (CITY) Study Group; CDE10. Effect of Continuous Glucose Monitoring on Glycemic Control in Adolescents and Young Adults With Type 1 Diabetes: A Randomized Clinical Trial. JAMA. 2020 Jun 16;323(23):2388-2396. doi: 10.1001/jama.2020.6940.

    PubMed 32543683

Questions about this trial

What is this clinical trial studying?

A Phase 3 study testing Continuous Glucose Monitor (CGM) in people with Type 1 Diabetes Mellitus, run by Jaeb Center for Health Research at 14 sites in United States.

The full registered description is in the About this study section and the official record.

Who may be eligible to take part?

The sponsor lists 10 inclusion and 15 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.

Is this clinical trial currently recruiting?

The record says: finished, as of the sponsor's last update on 9 Jul 2026. Status can change between updates, so confirm with the study contact before making plans.

Where is the study taking place?

The record lists 14 sites in United States. Whether a site is taking part right now should be confirmed with that site. See every site.

What are the possible benefits and risks?

They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.

What does this phase mean?

Phase 3 studies compare the treatment with the current standard treatment or a placebo in a large group, to confirm how well it works and watch for side effects.

Not every study follows the same path, and some studies (observational studies, device studies) have no phase.

Are results available for this study?

Yes. Results are posted in the registry (first posted 9 Jul 2026). A summary is in the For doctors view, and the full results are on ClinicalTrials.gov.

How can a doctor refer a patient or contact the research team?

The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.

What does the primary outcome measure?

Change in HbA1c From Baseline to 26 Weeks Adjusted for Baseline (time frame: 6 months). It is what the study was designed to measure, not a finding.

Where can I read the original study information?

On the ClinicalTrials.gov record for NCT03263494, which also lists 3 linked publications.

Does a listing mean the treatment is approved or proven to work?

No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.

How often is this information updated?

AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 9 Jul 2026.

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