Type 1 Diabetes

Type 1 diabetes is a form of diabetes mellitus characterized by severe deficiency of insulin, usually because the immune system destroys insulin-producing beta cells in the pancreas. Insulin replacement is essential for survival in established insulin-deficient disease. Although frequently diagnosed in children and adolescents, type 1 diabetes can develop at any age; the historical name “juvenile diabetes” therefore does not describe its full age range. (niddk.nih.gov)

Biological basis and causes

Type 1 diabetes is usually an autoimmune disease. The loss of pancreatic beta cells progressively reduces the body’s capacity to regulate blood glucose. Genetic susceptibility and environmental factors contribute to its development, but the precise triggers are not fully understood. Having an affected close relative increases risk, although inheritance does not determine whether the disease will occur. (niddk.nih.gov)

Diabetes-associated autoantibodies provide measurable evidence of the autoimmune process. Their presence can precede abnormal blood glucose and clinical symptoms, allowing the disease to be identified before the conventional diagnosis of symptomatic diabetes. (niddk.nih.gov)

Stages and clinical presentation

The staging framework for autoimmune type 1 diabetes distinguishes an early immune process from clinically established diabetes:

Progression varies between individuals, and stage 1 may persist for years. A single confirmed autoantibody generally indicates increased risk rather than meeting the usual definition of stage 1. (cdc.gov)

Typical symptoms include frequent urination, excessive thirst, unexplained weight loss, fatigue, and blurred vision. Symptoms often appear over days or weeks in children, whereas adult-onset disease may develop more slowly and initially resemble type 2 diabetes. Slowly progressing autoimmune diabetes in adults is sometimes described as latent autoimmune diabetes in adults, or LADA. (niddk.nih.gov)

Diagnosis and classification

Diagnosis involves both establishing diabetes and identifying its type. Standard laboratory thresholds for diabetes in nonpregnant individuals include:

• Fasting plasma glucose of 126 mg/dL (7.0 mmol/L) or higher.
• Plasma glucose of 200 mg/dL (11.1 mmol/L) or higher two hours after an oral glucose tolerance test.
• Glycated hemoglobin, or HbA1c, of 6.5% or higher.
• Random plasma glucose of 200 mg/dL (11.1 mmol/L) or higher in a person with characteristic symptoms.

Confirmation with another abnormal test is usually necessary when the initial findings are not unequivocal. These measurements establish diabetes but do not, by themselves, distinguish type 1 from type 2 or other forms. HbA1c reflects average glucose over approximately three months and can be affected by some blood disorders and other clinical circumstances. (niddk.nih.gov)

Autoantibody testing helps establish an autoimmune origin. When classification remains uncertain, C-peptide testing assesses the pancreas’s own insulin production, and genetic testing may help identify uncommon inherited forms of diabetes. (niddk.nih.gov)

Treatment and monitoring technologies

Established insulin-deficient type 1 diabetes is treated with externally supplied insulin. Delivery methods include injections and insulin pumps; glucose monitoring supplies information used to adjust treatment. Management aims to regulate glucose while limiting both excessive and insufficient glucose levels. (niddk.nih.gov)

Continuous glucose monitoring measures glucose in the fluid between cells through a sensor and provides repeated readings. An automated insulin delivery system combines a continuous glucose monitor, an insulin pump, and a control program that adjusts insulin delivery in response to sensor measurements. Such systems are also called artificial pancreas systems, although they do not replace the anatomical organ. (niddk.nih.gov)

Automation can improve glucose control and reduce some of the workload of diabetes management, but these systems are not entirely autonomous. They require device maintenance and, in many systems, meal information. Sensor or pump problems, skin irritation from adhesives, and episodes of high or low glucose remain possible. (niddk.nih.gov)

Complications

Diabetic ketoacidosis (DKA) is an acute, potentially life-threatening complication of insufficient insulin. The body breaks down fat for fuel, producing ketones that can accumulate and make the blood excessively acidic. Features include dehydration, nausea, vomiting, abdominal pain, fruity-smelling breath, and abnormal breathing. DKA may be the first recognized manifestation of type 1 diabetes. (cdc.gov)

Hypoglycemia, or low blood glucose, is particularly common in insulin-treated type 1 diabetes. Severe episodes can cause confusion, seizures, or loss of consciousness. Some people develop reduced awareness of the usual warning symptoms, complicating detection. (cdc.gov)

Long-term complications include damage to the eyes, kidneys, and nerves, as well as cardiovascular disease. The Diabetes Control and Complications Trial demonstrated that intensive glucose management reduced the development and progression of eye, kidney, and nerve complications. Its follow-up study, Epidemiology of Diabetes Interventions and Complications, documented lasting benefits, including reduced cardiovascular risk, from earlier intensive treatment. (niddk.nih.gov)

Disease-modifying and cell-replacement therapies

Disease-modifying treatment seeks to alter the autoimmune process or preserve remaining insulin production rather than simply replace insulin. Teplizumab, a monoclonal antibody, has a United States indication for delaying progression from stage 2 to stage 3 in eligible adults and children aged one year and older. On June 12, 2026, the Food and Drug Administration also granted accelerated approval for delaying the decline of insulin production in certain children aged 8–17 with recently diagnosed stage 3 disease. These indications concern delaying progression or preserving function, not eliminating established diabetes. (fda.gov)

Pancreatic islet transplantation introduces donor insulin-producing cells into a recipient. It can improve glucose regulation and reduce severe hypoglycemia in selected people with difficult-to-manage type 1 diabetes. Important limitations include donor availability, procedural risks, and the adverse effects of immunosuppressive medicines needed to protect the transplanted cells. Transplantation is therefore distinct from a broadly applicable cure. (niddk.nih.gov)

Historical development

The discovery of insulin at the University of Toronto in 1921 transformed the treatment of severe insulin-deficient diabetes. In January 1922, Leonard Thompson became the first patient successfully treated with the developing insulin preparation. Before insulin therapy, dietary restriction could sometimes prolong survival but could not correct the underlying deficiency. (utoronto.ca)

A later milestone was the Diabetes Control and Complications Trial, whose findings established the importance of sustained glucose management for preventing complications. The trial’s successor, the EDIC study, began in 1994 and extended the evidence from short-term glucose control to long-term health outcomes. (niddk.nih.gov)

References

1. Type 1 Diabetes - NIDDKniddk.nih.gov
2. Symptoms & Causes of Diabetes - NIDDKniddk.nih.gov
3. Story of Discovery: Progress on the Pathway to Prevention of Type 1 Diabetes - NIDDKniddk.nih.gov
4. Screening for Type 1 Diabetes - CDCcdc.gov
5. Table 2, Staging of Type 1 DM - Endotextncbi.nlm.nih.gov
6. Diabetes Tests & Diagnosis - NIDDKniddk.nih.gov
7. Artificial Pancreas - NIDDKniddk.nih.gov
8. Diabetic Ketoacidosis - CDCcdc.gov
9. Low Blood Sugar (Hypoglycemia) - CDCcdc.gov
10. Blood Glucose Control Studies for Type 1 Diabetes: DCCT & EDIC - NIDDKniddk.nih.gov
11. FDA Approves New Indication for Tzield (teplizumab) for Certain Pediatric Patients with Recently Diagnosed Stage 3 Type 1 Diabetesfda.gov
12. Pancreatic Islet Transplantation - NIDDKniddk.nih.gov