Type 1 Diabetes Mellitus
An autoimmune disease that destroys pancreatic beta cells until insulin secretion fails almost completely, so glucose rises unchecked and unopposed lipolysis drives ketone production: the mechanism behind both the presentation and the risk of diabetic ketoacidosis.
In a nutshell
Autoimmune destruction of beta cells causing absolute, not relative, insulin deficiency. Osmotic symptoms plus marked weight loss because insulin's anabolic role is also lost, and unopposed lipolysis makes ketoacidosis a real risk, sometimes as the presenting event.
Classic presentation
A child, adolescent or young adult with rapid-onset thirst, polyuria and weight loss over days to weeks, occasionally presenting first with diabetic ketoacidosis.
Key points
- Absolute insulin deficiency, not resistance, is the defining lesion: insulin sensitisers and secretagogues have no role.
- Weight loss is more prominent than in type 2 diabetes because insulin's anabolic (fat- and protein-sparing) role is lost alongside its glucose-lowering role.
- Unopposed lipolysis drives ketogenesis, so type 1 diabetics are prone to diabetic ketoacidosis in a way type 2 diabetics usually are not.
- Islet autoantibodies (anti-GAD, anti-IA2) support the diagnosis but their absence does not exclude type 1 diabetes.
- Insulin is required from diagnosis; sick-day rules must never mean omitting insulin, since illness increases requirements.
First-line investigation
Random or fasting plasma glucose (or HbA1c) alongside blood or urine ketones to exclude ketoacidosis at presentation.
First-line management
Immediate basal-bolus insulin replacement with structured education in carbohydrate counting and glucose monitoring.
Exam traps
- Never withhold insulin because a patient is not eating: omission, not food, is what precipitates ketoacidosis.
- Weight loss with osmotic symptoms in a young, lean patient should suggest type 1, not type 2, diabetes.
- A single normal glucose does not exclude type 1 diabetes early in the autoimmune process; recheck if suspicion remains.
Educational content pending clinical review. Not medical advice.