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Type 1 diabetes mellitus

Last reviewed: 23 May 2025
Last updated: 19 Jun 2025

Summary

Definition

History and exam

Key diagnostic factors

  • polyuria
  • polydipsia
  • diabetic ketoacidosis
Full details

Other diagnostic factors

  • young age
  • weight loss
  • blurred vision
  • nausea and vomiting
  • abdominal pain
  • tachypnea
  • clinical dehydration
  • lethargy
  • altered mental status
Full details

Risk factors

  • genetic predisposition
  • geographic region
  • infectious agents
  • dietary factors
  • use of immunotherapy
Full details

Diagnostic tests

1st tests to order

  • HbA1c
  • fasting plasma glucose
  • 2-hour post-glucose load plasma glucose
  • random plasma glucose
Full details

Tests to consider

  • plasma or urine ketones
  • random C-peptide
  • autoimmune markers
Full details

Treatment algorithm

ONGOING

nonpregnant

pregnant

Contributors

Authors

Rajesh K. Garg, MD
Rajesh K. Garg

Professor of Medicine

David Geffen School of Medicine at UCLA

Harbor-UCLA Medical Center

Torrance

CA

Disclosures

RKG is an author of a number of references cited in this topic.

Acknowledgements

Dr Rajesh K. Garg would like to gratefully acknowledge Dr Varsha Vimalananda, previous contributor to this topic.

Disclosures

VV declares that she has no competing interests.

Peer reviewers

Zachary Bloomgarden, MD

Clinical Professor

Medicine/Endocrinology

Diabetes and Bone Disease

Mount Sinai School of Medicine

New York

NY

Disclosures

ZB declares that he has no competing interests.

Alicia Jenkins, MB, BS, MD, FRACP, FRCP

Associate Professor

Department of Medicine

University of Melbourne

Melbourne

Australia

Professor

Harold Hamm Oklahoma Diabetes Center

University of Oklahoma Health Sciences Center

Oklahoma City

OK

Disclosures

AJ has been a (non-salaried) co-investigator on multi-center clinical trials supported by Novo, Eli Lilly, Sanofi-Aventis, and Medtronic. She does not hold any stocks or shares in these companies. She has received a speaker's honorarium from Novo Nordisk.

References

Our in-house evidence and editorial teams collaborate with international expert contributors and peer reviewers to ensure that we provide access to the most clinically relevant information possible.

Key articles

American Diabetes Association. Standards of care in diabetes - 2025. Diabetes Care. 2025 Jan;48(1):S344-52.Full text

Norris JM, Johnson RK, Stene LC. Type 1 diabetes-early life origins and changing epidemiology. Lancet Diabetes Endocrinol. 2020 Mar;8(3):226-38.Full text  Abstract

International Society for Pediatric and Adolescent Diabetes. ISPAD clinical practice consensus guidelines 2024. Dec 2024 [nternet publication].Full text

Holt RIG, DeVries JH, Hess-Fischl A, et al. The management of type 1 diabetes in adults. A consensus report by the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD). Diabetologia. 2021 Dec;64(12):2609-52.Full text  Abstract

Reference articles

A full list of sources referenced in this topic is available to users with access to all of BMJ Best Practice.
  • Type 1 diabetes mellitus images
  • Differentials

    • Monogenic diabetes: maturity onset diabetes of the young
    • Monogenic diabetes: neonatal diabetes mellitus
    • Type 2 diabetes
    More Differentials
  • Guidelines

    • Standards of care in diabetes - 2025
    • Management of individuals with diabetes at high risk for hypoglycemia
    More Guidelines
  • Patient information

    Diabetes type 1: what is it?

    Diabetes type 1: what treatments work?

    More Patient information
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