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# Type 1 diabetes mellitus

Type 1 diabetes is a disease in which the immune system destroys the insulin-making cells of the [pancreas](https://durgical.com/en/anatomy/pancreas/), so people with it need insulin for life.

Updated 2026-10-29

## Structures involved

Tap one to see what it is and open it in 3D.

- [Pancreas](https://durgical.com/en/anatomy/pancreas/)
- [Kidneys](https://durgical.com/en/anatomy/kidney/)
- [Retina](https://durgical.com/en/anatomy/retina/)
- [Liver](https://durgical.com/en/anatomy/liver/)
- [Macula](https://durgical.com/en/anatomy/macula/)
- [Vessels inside the kidney](https://durgical.com/en/anatomy/intrarenal-arteries-and-veins/)
- [Thyroid gland](https://durgical.com/en/anatomy/thyroid-gland/)

## In biochemistry

- [Glucose](https://durgical.com/en/biochemistry/molecules/glucose/)
- [Glycated haemoglobin (HbA1c)](https://durgical.com/en/biochemistry/topics/glycated-haemoglobin/)
- [Mitochondrial HMG-CoA synthase (HMGCS2)](https://durgical.com/en/biochemistry/enzymes/mitochondrial-hmg-coa-synthase/)
- [Acetoacetate (acetoacetic acid)](https://durgical.com/en/biochemistry/molecules/acetoacetate/)
- [β-Hydroxybutyrate](https://durgical.com/en/biochemistry/molecules/hydroxybutyrate/)
- [Insulin signalling](https://durgical.com/en/biochemistry/topics/insulin-signalling/)
- [Glucagon signalling](https://durgical.com/en/biochemistry/topics/glucagon-signalling/)
- [Recombinant DNA and cloning](https://durgical.com/en/biochemistry/topics/recombinant-dna-and-cloning/)

## In immunology

- [Type IV hypersensitivity (delayed, T cells)](https://durgical.com/en/immunology/type-iv-hypersensitivity/)
- [Immune tolerance and how autoimmunity begins](https://durgical.com/en/immunology/immune-tolerance-and-how-autoimmunity-begins/)
- [Autoantibodies: the table to know](https://durgical.com/en/immunology/autoantibodies-the-table-to-know/)
- [HLA associations with disease](https://durgical.com/en/immunology/hla-associations-with-disease/)
- [MHC/HLA class I and II](https://durgical.com/en/immunology/mhc-hla-class-i-and-ii/)

## In histology

- [Pancreas: acini and islets](https://durgical.com/en/histology/pancreas-acini-and-islets/)
- [Islets of Langerhans: α, β, δ cells](https://durgical.com/en/histology/islets-of-langerhans-cells/)

## In embryology

- [Maternal diabetes and obesity as teratogens](https://durgical.com/en/embryology/maternal-diabetes-and-obesity-as-teratogens/)

## In physiology

- [Islets and insulin: secretion and actions](https://durgical.com/en/physiology/islets-and-insulin-secretion-and-actions/)
- [Physiology of diabetes and ketoacidosis](https://durgical.com/en/physiology/physiology-of-diabetes-and-ketoacidosis/)
- [Glucagon and the counter-regulatory hormones](https://durgical.com/en/physiology/glucagon-and-the-counter-regulatory-hormones/)
- [The physiological response to hypoglycemia](https://durgical.com/en/physiology/the-physiological-response-to-hypoglycemia/)
- [Blood glucose, glucose tolerance test and HbA1c](https://durgical.com/en/physiology/blood-glucose-glucose-tolerance-test-and-hba1c/)
- [The enteric nervous system, slow waves and GI control](https://durgical.com/en/physiology/the-enteric-nervous-system-slow-waves-and-gi-control/)
- [Gastric motility and emptying](https://durgical.com/en/physiology/gastric-motility-and-emptying/)
- [Fed and fasting states: the hormonal switch](https://durgical.com/en/physiology/fed-and-fasting-states-the-hormonal-switch/)
- [Glucose transport maximum and renal threshold](https://durgical.com/en/physiology/glucose-transport-maximum-and-renal-threshold/)
- [Urine dilution, free water and osmotic diuresis](https://durgical.com/en/physiology/urine-dilution-free-water-and-osmotic-diuresis/)

## Why it happens

- [Multifactorial (complex) disorders](https://durgical.com/en/general-pathology/multifactorial-disorders/)
- [What delays healing: infection, diabetes, nutrition, glucocorticoids, poor blood flow](https://durgical.com/en/general-pathology/what-delays-healing-infection-diabetes-nutrition-glucocorticoids-poor-blood-flow/)

## What it is

A chronic disease in which the immune system destroys the insulin-producing beta cells of the pancreas, causing absolute insulin deficiency. People with it need insulin for life.

## Who gets it

Usually begins in childhood or adolescence, but can start at any age. It is much less common than type 2 diabetes, and frequency varies widely between countries.

## Causes

- Autoimmune destruction of pancreatic beta cells (type 1A), with islet autoantibodies
- Genetic susceptibility, especially certain HLA types
- Environmental triggers such as viral infections are suspected but not proven
- Rarely idiopathic, without autoantibodies (type 1B)

## Risk factors

- Parent or sibling with type 1 diabetes
- Other autoimmune diseases (autoimmune thyroid disease, celiac disease, Addison disease)
- Presence of islet autoantibodies in screening studies

## Pathophysiology

T cells attack the islets over months or years, often silently. When most beta-cell mass is lost, insulin is absent: glucose cannot enter cells, the [liver](https://durgical.com/en/anatomy/liver/) releases glucose and fat breakdown produces ketone bodies. Without insulin this leads to hyperglycaemia, osmotic diuresis, dehydration and ketoacidosis.

## Classification

- Stage 1: two or more autoantibodies, normal glucose, no symptoms
- Stage 2: autoantibodies with abnormal glucose, no symptoms
- Stage 3: clinical diabetes with symptoms
- Latent autoimmune diabetes in adults (LADA): slower autoimmune form in adults

## Symptoms and signs

- Polyuria, polydipsia and excessive hunger (polyphagia)
- Weight loss despite eating well
- Fatigue and blurred vision
- New bedwetting in a child who was previously dry
- Nausea, vomiting and abdominal pain when ketoacidosis develops

## Red flags

- Rapid deep breathing (Kussmaul breathing) or a fruity breath odour
- Vomiting, abdominal pain, drowsiness or confusion with high glucose
- Signs of dehydration or shock
- Hypoglycaemia with confusion, seizures or loss of consciousness

## Diagnosis

**Clinical**
Classic symptoms, often in a young, lean person; about a third of children or more are first diagnosed in diabetic ketoacidosis. Assess hydration, breathing pattern and consciousness.

**Tests**
Glucose (fasting, random with symptoms or HbA1c) confirms diabetes. Islet autoantibodies (GAD65, IA-2, insulin, ZnT8) and a low C-peptide support type 1. In acute illness: blood ketones, blood gas, electrolytes and [kidney](https://durgical.com/en/anatomy/kidney/) function. Screening for thyroid and celiac disease.

**Imaging**
Not needed for diagnosis. Retinal examination screens for retinopathy once the disease is established.

## Differential diagnosis

- Type 2 diabetes (especially in overweight adolescents)
- Monogenic diabetes (MODY or neonatal diabetes)
- Diabetes from pancreatic disease or cystic fibrosis
- Ketosis-prone type 2 diabetes
- Other causes of polyuria such as diabetes insipidus

## Goal of treatment

Replace insulin as closely as possible to normal physiology, keep glucose in target while avoiding hypoglycaemia, and prevent ketoacidosis and long-term complications.

## Treatment

**Medical**
Lifelong insulin, usually as a basal-bolus regimen (long-acting plus rapid-acting insulin at meals) or by continuous subcutaneous insulin infusion (pump).

**Acute**
Diabetic ketoacidosis is treated in hospital with intravenous fluids, intravenous insulin, potassium replacement and close monitoring, while looking for the trigger.

**Follow-up**
Capillary glucose testing or continuous glucose monitoring, regular HbA1c, and screening for retinopathy, kidney disease, neuropathy, thyroid and celiac disease.

**Lifestyle**
Education in carbohydrate counting, adjusting insulin to food and exercise, recognising and treating hypoglycaemia, and sick-day rules.

## Drugs for this condition

- [Regular human insulin](https://durgical.com/en/pharmacology/regular-human-insulin/)
- [Isophane (NPH) insulin](https://durgical.com/en/pharmacology/isophane-insulin/)
- [Insulin glargine](https://durgical.com/en/pharmacology/insulin-glargine/)
- [Insulin lispro](https://durgical.com/en/pharmacology/insulin-lispro/)
- [Insulin aspart](https://durgical.com/en/pharmacology/insulin-aspart/)
- [Insulin degludec](https://durgical.com/en/pharmacology/insulin-degludec/)
- [Insulin detemir](https://durgical.com/en/pharmacology/insulin-detemir/)
- [Insulin glulisine](https://durgical.com/en/pharmacology/insulin-glulisine/)
- [Pramlintide](https://durgical.com/en/pharmacology/pramlintide/)

## Complications

- Diabetic ketoacidosis
- Hypoglycaemia, including unawareness of hypoglycaemia
- Retinopathy, nephropathy and neuropathy
- Coronary, cerebrovascular and peripheral artery disease
- Cerebral oedema during ketoacidosis treatment, mainly in children

## Prognosis

With modern insulin, education and monitoring, most people lead full lives. Long-term outcome depends on glucose control and cardiovascular risk management; complications become more likely with longer disease duration and poor control.

## Test yourself

Think of the answer, then tap the question to see it.

## What is the basic mechanism of type 1 diabetes?

Autoimmune destruction of pancreatic beta cells, causing absolute insulin deficiency.

## Which laboratory findings help distinguish type 1 from type 2 diabetes?

Positive islet autoantibodies (GAD65, IA-2, insulin, ZnT8) and low or undetectable C-peptide point to type 1.

## What is the classic triad of diabetic ketoacidosis?

Hyperglycaemia, ketosis (ketonaemia or ketonuria) and high anion gap metabolic acidosis.

## Why must potassium be watched closely when treating diabetic ketoacidosis?

Total body potassium is depleted, and insulin drives potassium into cells, so serum potassium can fall dangerously during treatment.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/conditions/type-1-diabetes-mellitus/)

## Related conditions

- [Type 2 diabetes mellitus](https://durgical.com/en/conditions/type-2-diabetes-mellitus/)
- [Coeliac disease](https://durgical.com/en/conditions/coeliac-disease/)
- [Adrenal insufficiency](https://durgical.com/en/conditions/adrenal-insufficiency/)
- [Cataract](https://durgical.com/en/conditions/cataract/)
- [Diabetic retinopathy](https://durgical.com/en/conditions/diabetic-retinopathy/)
- [Dupuytren contracture](https://durgical.com/en/conditions/dupuytren-contracture/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Type 1 Diabetes](https://www.ncbi.nlm.nih.gov/books/NBK507713/) (StatPearls (NCBI Bookshelf), 2024).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/conditions/type-1-diabetes-mellitus/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/type-1-diabetes-mellitus/