Review

. 2025 Jul;19(4):1109-1127.

doi: 10.1177/19322968251333441. Epub 2025 May 30.

The Use of Continuous Glucose Monitoring to Diagnose Stage 2 Type 1 Diabetes

Julia K Mader¹, Jenise C Wong², Guido Freckmann³, Jose Garcia-Tirado^{4

5}, Irl B Hirsch⁶, Suzanne Bennett Johnson⁷, David Kerr⁸, Sun H Kim⁹, Rayhan Lal⁹, Eslam Montaser¹⁰, Holly O'Donnell¹¹, Stefan Pleus³, Viral N Shah¹⁰, Alessandra T Ayers¹², Cindy N Ho¹², Torben Biester¹³, Klemen Dovc^{14

15}, Farnoosh Farrokhi¹⁶, Alexander Fleming¹⁷, Pieter Gillard¹⁸, Lutz Heinemann¹⁹, Raquel López-Díez²⁰, David M Maahs²¹, Chantal Mathieu¹⁸, Zoe Quandt²², Birgit Rami-Merhar²³, Wendy Wolf²⁴, David C Klonoff²⁵

Affiliations

¹ Division of Endocrinology and Diabetology, Department of Internal Medicine, Medical University of Graz, Graz, Austria.
² Division of Endocrinology, Department of Pediatrics, University of California, San Francisco, San Francisco, CA, USA.
³ Institut für Diabetes-Technologie, Forschungs- und Entwicklungsgesellschaft mbH an der Universität Ulm, Ulm, Germany.
⁴ University Clinic for Diabetes, Endocrinology, Nutritional Medicine, and Metabolism, Inselspital-University Hospital Bern, University of Bern, Bern, Switzerland.
⁵ Diabetes Center Berne, Bern, Switzerland.
⁶ Division of Metabolism, Endocrinology, and Nutrition, Department of Medicine, University of Washington School of Medicine, Seattle, WA, USA.
⁷ Department of Behavioral Sciences and Social Medicine, College of Medicine, Florida State University, Tallahassee, FL, USA.
⁸ Center for Health Systems Research, Sutter Health, Santa Barbara, CA, USA.
⁹ Division of Endocrinology, Gerontology and Metabolism, Stanford University School of Medicine, Stanford University, Stanford, CA, USA.
¹⁰ Division of Endocrinology and Metabolism, Indiana University School of Medicine, Indianapolis, IN, USA.
¹¹ Department of Pediatrics, Barbara Davis Center for Diabetes, University of Colorado School of Medicine, Aurora, CO, USA.
¹² Diabetes Technology Society, Burlingame, CA, USA.
¹³ AUF DER BULT, Hospital for Children and Adolescents, Hannover, Germany.
¹⁴ Department of Endocrinology, Diabetes and Metabolism, University Children's Hospital, University Medical Centre Ljubljana, Ljubljana, Slovenia.
¹⁵ Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia.
¹⁶ Department of Endocrinology, Diabetes, and Metabolism, Alta Bates Summit Medical Center, Sutter East Bay Medical Group, Orinda, CA, USA.
¹⁷ Kinexum, Harpers Ferry, WV, USA.
¹⁸ Department of Endocrinology, University Hospitals Leuven-KU Leuven, Leuven, Belgium.
¹⁹ Science Consulting in Diabetes GmbH, Düsseldorf, Germany.
²⁰ Breakthrough T1D (formerly JDRF International), New York, NY, USA.
²¹ Department of Pediatrics, Stanford University, Stanford, CA, USA.
²² Diabetes Center and Department of Medicine, Endocrinology, University of California, San Francisco, San Francisco, CA, USA.
²³ Department of Pediatric and Adolescent Medicine, Comprehensive Center for Pediatrics, Medical University of Vienna, Vienna, Austria.
²⁴ T1D Exchange, Boston, MA, USA.
²⁵ Diabetes Research Institute, Mills-Peninsula Medical Center, San Mateo, CA, USA.

PMID: 40444471
PMCID: PMC12125016
DOI: 10.1177/19322968251333441

Review

The Use of Continuous Glucose Monitoring to Diagnose Stage 2 Type 1 Diabetes

Julia K Mader et al. J Diabetes Sci Technol. 2025 Jul.

. 2025 Jul;19(4):1109-1127.

doi: 10.1177/19322968251333441. Epub 2025 May 30.

Authors

Affiliations

¹ Division of Endocrinology and Diabetology, Department of Internal Medicine, Medical University of Graz, Graz, Austria.
² Division of Endocrinology, Department of Pediatrics, University of California, San Francisco, San Francisco, CA, USA.
³ Institut für Diabetes-Technologie, Forschungs- und Entwicklungsgesellschaft mbH an der Universität Ulm, Ulm, Germany.
⁴ University Clinic for Diabetes, Endocrinology, Nutritional Medicine, and Metabolism, Inselspital-University Hospital Bern, University of Bern, Bern, Switzerland.
⁵ Diabetes Center Berne, Bern, Switzerland.
⁶ Division of Metabolism, Endocrinology, and Nutrition, Department of Medicine, University of Washington School of Medicine, Seattle, WA, USA.
⁷ Department of Behavioral Sciences and Social Medicine, College of Medicine, Florida State University, Tallahassee, FL, USA.
⁸ Center for Health Systems Research, Sutter Health, Santa Barbara, CA, USA.
⁹ Division of Endocrinology, Gerontology and Metabolism, Stanford University School of Medicine, Stanford University, Stanford, CA, USA.
¹⁰ Division of Endocrinology and Metabolism, Indiana University School of Medicine, Indianapolis, IN, USA.
¹¹ Department of Pediatrics, Barbara Davis Center for Diabetes, University of Colorado School of Medicine, Aurora, CO, USA.
¹² Diabetes Technology Society, Burlingame, CA, USA.
¹³ AUF DER BULT, Hospital for Children and Adolescents, Hannover, Germany.
¹⁴ Department of Endocrinology, Diabetes and Metabolism, University Children's Hospital, University Medical Centre Ljubljana, Ljubljana, Slovenia.
¹⁵ Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia.
¹⁶ Department of Endocrinology, Diabetes, and Metabolism, Alta Bates Summit Medical Center, Sutter East Bay Medical Group, Orinda, CA, USA.
¹⁷ Kinexum, Harpers Ferry, WV, USA.
¹⁸ Department of Endocrinology, University Hospitals Leuven-KU Leuven, Leuven, Belgium.
¹⁹ Science Consulting in Diabetes GmbH, Düsseldorf, Germany.
²⁰ Breakthrough T1D (formerly JDRF International), New York, NY, USA.
²¹ Department of Pediatrics, Stanford University, Stanford, CA, USA.
²² Diabetes Center and Department of Medicine, Endocrinology, University of California, San Francisco, San Francisco, CA, USA.
²³ Department of Pediatric and Adolescent Medicine, Comprehensive Center for Pediatrics, Medical University of Vienna, Vienna, Austria.
²⁴ T1D Exchange, Boston, MA, USA.
²⁵ Diabetes Research Institute, Mills-Peninsula Medical Center, San Mateo, CA, USA.

PMID: 40444471
PMCID: PMC12125016
DOI: 10.1177/19322968251333441

Abstract

This consensus report evaluates the potential role of continuous glucose monitoring (CGM) in screening for stage 2 type 1 diabetes (T1D). CGM offers a minimally invasive alternative to venous blood testing for detecting dysglycemia, facilitating early identification of at-risk individuals for confirmatory blood testing. A panel of experts reviewed current evidence and addressed key questions regarding CGM's diagnostic accuracy and screening protocols. They concluded that while CGM cannot yet replace blood-based diagnostics, it holds promise as a screening tool that could lead to earlier, more effective intervention. Metrics such as time above range >140 mg/dL could indicate progression risk, and artificial intelligence (AI)-based modeling may enhance predictive capabilities. Further research is needed to establish CGM-based diagnostic criteria and refine screening strategies to improve T1D detection and intervention.

Keywords: CGM; artificial intelligence; machine learning; stage 2 T1D; teplizumab.

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Conflict of interest statement

Declaration of Conflicting InterestsThe author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: JKM is a member of advisory boards of Abbott Diabetes Care, Becton-Dickinson, Biomea Fusion, DexCom, Eli Lilly, Embecta, Medtronic, myLife, Novo Nordisk A/S, Pharmasens, Roche Diabetes Care, Sanofi-Aventis, Tandem, and Viatris and received speaker honoraria from A. Menarini Diagnostics, Abbott Diabetes Care, DexCom, Eli Lilly, Medtrust, MSD, Novo Nordisk A/S, Roche Diabetes Care, Sanofi, Viatris, and Ypsomed. She is a shareholder of decide Clinical Software GmbH and elyte Diagnostics and serves as CMO of elyte Diagnostics. JCW has no relevant disclosures. GF is general manager and medical director of the IfDT (Institut fürDiabetes-Technologie, Forschungs- und Entwicklungsgesellschaft mbH ander Universität Ulm, Ulm, Germany), which carries out clinical studies, eg, with medical devices for diabetes therapy on its own initiative and on behalf of various companies. GF/IfDT have received research support, speakers’ honoraria or consulting fees in the last three years from Abbott, Ascensia, Berlin Chemie, Boydsense, DexCom, Glucoset, i-SENS, Lilly, Menarini, Novo Nordisk, Perfood, Pharmasens, Roche, Sinocare, Terumo, and Ypsomed. JG-T reports receiving royalties from DexCom. IBH has received research support from Mannkind, DexCom, and Tandem. IBH is a consultant for Abbott, Roche, and Hagar. SBJ is a consultant to Breakthrough T1D and is the Psychosocial Committee Chair for TEDDY and TrialNet. DK’s institution has received research support from Abbott Diabetes Care. SHK is a consultant for TeCure and has received educational funding from Novo Nordisk. RL is a consultant for Abbott Diabetes Care, Adaptyx Biosciences, Biolinq, Capillary Biomedical, Deep Valley Labs, Gluroo, PhysioLogic Devices, Portal Insulin, Sanofi, and Tidepool. RL is on the advisory board for ProventionBio and Lilly. RL has received research support to his university from Insulet, Medtronic, Tandem, and Sinocare. EM has nothing to declare. HO has received consulting fees from Sanofi. SP is the employee of IfDT. VNS’ institution has received research support from Enable Bioscience, Zucara Therapeutics, Eli Lilly, Cystic Fibrosis Foundation, Breakthrough T1D, and NIH. VNS has received personal fees from Sanofi, Novo Nordisk, Eli Lilly, DexCom, Insulet, Tandem Diabetes Care, Ascensia Diabetes Care, Biomea Fusion, Sequel Med Tech, Genomelink, and Lumosfit. ATA is a consultant for Liom. CNH is a consultant for Liom. TB has received speaker fees from Abbott, DexCom, Insulet, Lilly Deutschland, Medtronic, Novo Nordisk, Roche, Sanofi, Synlab, Tandem, Ypsomed, and Vitalaire; is on the advisory board for Ascensia, DexCom, Medtronic, Insulet, Sanofi, Tandem, and Ypsomed; has received study support from DexCom and Ypsomed; and is chair of the EXPAMED Panel Endo/Diabetes for new medical devices of EMA. KD has participated on a Data Safety Monitoring Board or Advisory Board for Novo Nordisk and Medtronic. KD has received payment or honoraria for lectures, presentations, or speakers’ bureaus from Abbott, DexCom, Eli Lilly, Medtronic, Novo Nordisk, and Pfizer. FF has no relevant conflicts of interest. AF has no relevant conflicts of interest. PG has received grants from Novo Nordisk, Sanofi, DexCom, Tandem, Abbott, Medtronic, and Roche. Consultancy fees have been provided by Abbott, Medtronic, and Bayer. Payments or honoraria for lectures, presentations, speakers, bureaus, manuscript writing, or educational events have been received from Medtronic, Novo Nordisk, Abbott, Ypsomed, Vitalaire, DexCom, Bayer, and Insulet. Support for attending meetings and/or travel has been provided by Sanofi, Novo Nordisk, Medtronic, and Roche. Participation on advisory boards has resulted in payments from Insulet, DexCom, and Ypsomed. In addition, the institution of PG has received equipment, including DexCom CGMs for the ALERTT1 trial and Medtronic 780G devices for the CRISTAL trial, with both sets of devices provided by the respective sponsors. LH is a consultant for Abbott, Lifecare (also a member of the Board of Directors), Medtronic EU Advisory Board, DexCom Germany, Roche Diagnostics, Liom, and Perfood. He is a shareholder of the Profil Institut für Stoffwechselforschung GmbH, Neuss, Germany, Science Consulting in Diabetes GmbH, Düsseldorf, Germany, and diateam GmbH, Bad Mergentheim, Germany. RL-D has no relevant conflicts of interest. DMM has had research support from the NIH, JDRF, NSF, and the Helmsley Charitable Trust, and his institution has had research support from Medtronic, DexCom, Insulet, Bigfoot Biomedical, Tandem, and Roche. DMM has consulted for Abbott, Aditxt, the Helmsley Charitable Trust, Lifescan, Mannkind, Sanofi, Novo Nordisk, Eli Lilly, Medtronic, Insulet, Dompe, Biospex, Provention Bio, Kriya, Enable Biosciences, and Bayer. CM serves or has served on the advisory panel for Novo Nordisk, Sanofi, Eli Lilly and Company, Novartis, DexCom, Boehringer Ingelheim, Bayer, Roche, Abbott, Medtronic, Insulet, Biomea Fusion, SAB Bio, and Vertex. Financial compensation for these activities has been received by KU Leuven; KU Leuven has received research support for CM from Medtronic, Novo Nordisk, and Sanofi; CM serves or has served on the speaker’s bureau for Novo Nordisk, Sanofi, Eli Lilly and Company, Medtronic, DexCom, Insulet, Abbott, Vertex, and Boehringer Ingelheim. Financial compensation for these activities has been received by KU Leuven. CM is president of EASD. All external support of EASD is to be found on www.easd.org. ZQ participated in a Sanofi Advisory Board in 2023. BR-M has been on advisory boards for or received speaker honorarium from Abbott, Medtronic, Sanofi, Eli Lilly, Insulet, DexCom, INNODIA iVZW, and Ypsomed in the last 3 years. WW has no relevant disclosures to report. DCK is a consultant for Afon, embecta, Glucotrack, Lifecare, Novo, Samsung, SynchNeuro, and Thirdwayv.

Figures

**Figure 1.**
Transition probability matrices for two individuals: autoantibody-negative (a) vs autoantibody-positive (b). (a) Weighted average transition probability matrix for an autoantibody-negative individual with a low entropy rate (0.08). The x- and y-axes represent eight glycemic states based on mean CGM glucose (MG): (a) MG <54 mg/dL, (b) 54≤MG<69 mg/dL, (c) 70≤MG<120 mg/dL, (d) 121≤MG<140 mg/dL, (e) 141≤MG<160 mg/dL, (f) 161≤MG<180 mg/dL, (g) 181≤MG<250 mg/dL, and (h) MG >250 mg/dL. All glycemia remain in low-risk zones (c and d), indicating stable glycemic control. (B) Weighted average transition probability matrix for an autoantibody-positive individual (with two or more autoantibodies) and a high entropy rate (0.96). Glycemia spans across zones (a to e), with progression to higher-risk zones (f and g), reflecting increased GV and risk. Colored zones indicate the probability of transitioning between glycemic states.

See this image and copyright information in PMC

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The Use of Continuous Glucose Monitoring to Diagnose Stage 2 Type 1 Diabetes

Affiliations

The Use of Continuous Glucose Monitoring to Diagnose Stage 2 Type 1 Diabetes

Authors

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Conflict of interest statement

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