Diabetes: Basics

Related Subjects: |Diabetes Mellitus: Basics |Type 1 Diabetes Mellitus | Type 2 Diabetes Mellitus | Type 3c Diabetes Mellitus |Gestational Diabetes |HbA1c |Hyperglycaemic Hyperosmolar State (HHS) |Diabetic Nephropathy |Diabetic Retinopathy |Diabetic Neuropathy |Diabetic Amyotrophy |Maturity Onset Diabetes of the Young (MODY) |Diabetes: Complications |Hypoglycaemia |Diabetic Ketoacidosis (DKA) Adults |Alcoholic Ketoacidosis |Euglycaemic Ketoacidosis (euDKA) with SGLT2 Inhibitors |Causes of Ketoacidosis

🩸 Diabetes mellitus is a group of conditions where the blood glucose level is too high. This happens because the body either does not produce enough insulin, does not respond properly to insulin, or both.

📖 What is Diabetes?

• Glucose is an important fuel for the body.
• Insulin is a hormone made by pancreatic ß-cells.
• Insulin helps move glucose from the blood into cells.
• If insulin is absent or ineffective, glucose stays in the blood → hyperglycaemia.
• Long-term hyperglycaemia can damage blood vessels, nerves, kidneys, eyes and the heart.

🧬 Main Types of Diabetes

• Type 1 diabetes: Autoimmune ß-cell destruction → absolute insulin deficiency.
• Type 2 diabetes: Insulin resistance plus progressive ß-cell dysfunction.
• Gestational diabetes: Diabetes first diagnosed during pregnancy.
• Type 3c diabetes: Diabetes caused by pancreatic disease or pancreatic damage.
• Other secondary diabetes: Diabetes due to drugs, endocrine disease or genetic conditions.

💉 Type 1 Diabetes

• Usually autoimmune.
• The pancreas produces little or no insulin.
• Often presents in children, teenagers or young adults, but can occur at any age.
• Symptoms often develop quickly: polyuria, polydipsia, weight loss and fatigue.
• Patients require lifelong insulin.
• Risk of diabetic ketoacidosis if insulin is missed or insufficient.

🍎 Type 2 Diabetes

• The commonest type of diabetes.
• Usually caused by insulin resistance with gradual ß-cell failure.
• Often associated with overweight, obesity, increasing age, family history and some ethnic backgrounds.
• May be asymptomatic for years.
• Managed with lifestyle measures, oral medication, injectable therapies and sometimes insulin.
• Risk of long-term vascular complications if not well controlled.

🤰 Gestational Diabetes

• Diabetes first recognised during pregnancy.
• Placental hormones increase insulin resistance, especially in the 2nd and 3rd trimester.
• NICE diagnosis uses a 75 g oral glucose tolerance test.
• Diagnostic thresholds: fasting glucose ≥5.6 mmol/L or 2-hour glucose ≥7.8 mmol/L.
• Usually improves after delivery, but future type 2 diabetes risk is increased.
• Management includes diet, glucose monitoring, metformin or insulin if needed.

🫀 Type 3c Diabetes

• Also called pancreatogenic diabetes.
• Caused by damage to the pancreas.
• Causes include chronic pancreatitis, pancreatic cancer, cystic fibrosis, haemochromatosis or pancreatic surgery.
• Patients may have insulin deficiency and pancreatic enzyme deficiency.
• Can be mistaken for type 2 diabetes.
• May need insulin and pancreatic enzyme replacement therapy if malabsorption is present.

💊 Secondary Diabetes

• Some diabetes is caused by another medical problem or medication.
• Drug causes: Corticosteroids, some antipsychotics, immunosuppressants and some cancer treatments.
• Endocrine causes: Cushing’s syndrome, acromegaly, phaeochromocytoma and hyperthyroidism.
• Genetic causes: MODY and neonatal diabetes.

🔍 Key Differences

🩺 Common Symptoms of Diabetes

• Polyuria — passing urine frequently.
• Polydipsia — excessive thirst.
• Unexplained weight loss.
• Tiredness.
• Blurred vision.
• Recurrent infections, such as thrush or skin infections.
• Slow wound healing.

🧪 Diagnosis

• Diabetes can be diagnosed using HbA1c, fasting plasma glucose, random plasma glucose with symptoms, or an oral glucose tolerance test.
• HbA1c ≥48 mmol/mol, equivalent to 6.5%, supports a diagnosis of diabetes in many non-pregnant adults.
• Random plasma glucose ≥11.1 mmol/L with symptoms supports diabetes.
• Fasting plasma glucose ≥7.0 mmol/L supports diabetes.
• In pregnancy, NICE uses specific OGTT thresholds for gestational diabetes.
• Ketones should be checked urgently if type 1 diabetes or DKA is suspected.

⚠️ Complications

• Acute: Hypoglycaemia, diabetic ketoacidosis and hyperosmolar hyperglycaemic state.
• Eyes: Diabetic retinopathy.
• Kidneys: Diabetic kidney disease.
• Nerves: Peripheral neuropathy and autonomic neuropathy.
• Feet: Ulcers, infection and amputation risk.
• Cardiovascular: Myocardial infarction, stroke and peripheral arterial disease.

🛠️ General Management Principles

• Identify the correct type of diabetes.
• Agree individualised glucose targets.
• Support healthy eating, physical activity and weight management where appropriate.
• Use medication based on diabetes type, comorbidities and patient preference.
• Screen for eye, kidney, nerve, foot and cardiovascular complications.
• Educate patients on hypoglycaemia, sick-day rules and when to seek urgent help.

🚩 Red Flags

• Vomiting, abdominal pain or drowsiness with high glucose or ketones.
• Rapid weight loss with thirst and polyuria.
• New diabetes with ketones.
• Pregnancy with hyperglycaemia or ketones.
• Foot ulcer, spreading cellulitis or systemic infection.
• New diabetes with jaundice, persistent abdominal pain or unexplained weight loss — consider pancreatic cancer.

🧠 Exam Pearls

• Type 1 diabetes = autoimmune ß-cell destruction and absolute insulin deficiency.
• Type 2 diabetes = insulin resistance plus progressive ß-cell dysfunction.
• Gestational diabetes = pregnancy-related insulin resistance.
• Type 3c diabetes = pancreatic damage causing diabetes.
• Do not assume all adult-onset diabetes is type 2.
• Ketones plus acidosis means DKA until proven otherwise.

📚 Summary

Diabetes mellitus is not one disease but a group of conditions causing chronic hyperglycaemia. The key difference is the underlying mechanism: type 1 is insulin deficiency, type 2 is insulin resistance, gestational diabetes is pregnancy-related insulin resistance, and type 3c is caused by pancreatic damage. Correct classification matters because treatment, complication risk and patient education differ.