The aim of the China Diabetes Type 1 Study (CD1S) is to conduct a nationwide type 1 diabetes (T1D) registry study in patients with T1D and in pediatric adolescent patients with diabetes who had an age of onset <= 20 years.

CD1S compromises a retrospective study enrolling inpatients hospitalized from Jan 1st, 2016 to Dec 31, 2021, and a prospective study beginning from the year 2022.

The aim of the China Diabetes Type 1 Study (CD1S) is to conduct a nationwide type 1 diabetes (T1D) registry study to investigate the demographic characteristics, metabolic control, complications occurrence as well as risk factors of patients with T1D, and to investigate the clinical features, complications' burdens and risk factors in pediatric adolescent patients with diabetes who had an age of onset <= 20 years.

Inclusion Criteria:

• 1. Patients with type 1 diabetes mellitus of any duration; meeting criteria (1) or any of (2) or any of (3)

  1. Clinical diagnosis of type 1 diabetes by a specialist
  2. Age at onset < 15 years; no overweight or obesity at onset; previous diabetic ketoacidosis; highest random C-peptide < 200 pmol/L
  3. Initiation and continuation of insulin therapy (except pancreatic or islet transplantation) after diagnosis; positive islet autoantibodies Or 2. Children and adolescents with diabetes mellitus at age of onset <= 20 years, regardless of type and duration of disease.

Exclusion Criteria:

• For enrolment of patients with T1D, exclusion was made if any of the following criteria were met (not applicable to those with onset under 20 years of age)

  • No insulin dependence for at least 6 months after diagnosis of diabetes mellitus.

    • No DKA for 1 month off insulin for those with a history of diabetes > 1 year. ③ C-peptide > 800 pmol/L at any time point.

Patients with type 1 diabetes or children and adolescents with diabetes mellitus at age of onset <= 20 years