Type 1 Diabetes — Causes, Symptoms, Insulin Therapy & Management Guide — Symptoms, Causes & Treatment | MyMedicPlus

Type 1 diabetes mellitus (T1DM) is a chronic autoimmune disease characterised by T-cell mediated destruction of the insulin-producing beta cells of the pancreatic islets of Langerhans, resulting in absolute insulin deficiency. Without exogenous insulin replacement, T1DM leads to life-threatening diabetic ketoacidosis (DKA). T1DM accounts for approximately 5-10% of all diabetes cases globally — affecting around 8.4 million people — and is the most common form of diabetes in children and young adults, though it can develop at any age (latent autoimmune diabetes in adults — LADA — presents similarly in adults over 30). The incidence of T1DM is rising by approximately 3-4% annually in high-income countries. Unlike Type 2 diabetes, T1DM is not preventable through lifestyle modification. With modern insulin regimens, continuous glucose monitoring (CGM), and closed-loop artificial pancreas systems, people with T1DM can achieve excellent glycaemic control and near-normal life expectancy, though the condition requires lifelong vigilance and daily management.

T1DM results from a complex interaction between genetic susceptibility and environmental triggers. Genetic factors: HLA-DR3-DQ2 and HLA-DR4-DQ8 haplotypes account for 40-50% of genetic risk (non-HLA genes: INS, PTPN22, CTLA4 contribute further); concordance in identical twins is 30-50% — demonstrating essential environmental contribution. Environmental triggers: viral infections (enterovirus — especially Coxsackievirus B4 — and Epstein-Barr virus have been implicated through molecular mimicry or direct beta cell damage); early introduction of cow's milk proteins; wheat gluten; and gut microbiome alterations. T1DM susceptibility genes are shared with coeliac disease (also HLA-DQ2/DQ8 associated — 5-10% of T1DM patients have coeliac disease — screen regularly). Islet autoantibodies (anti-GAD, anti-IA2, anti-ZnT8, anti-insulin) appear years before clinical onset — marking the pre-diabetic autoimmune phase. Three stages: Stage 1 (multiple autoantibodies, normoglycaemia); Stage 2 (dysglycaemia without symptoms); Stage 3 (clinical T1DM). Teplizumab (anti-CD3 antibody, FDA approved 2022) delays Stage 3 onset by median 2 years in high-risk Stage 2 individuals.

Classic triad of hyperglycaemia symptoms — 'the 4 Ts': Thirst (polydipsia), Toilet (polyuria), Tiredness (fatigue), and Thinner (unexplained weight loss). Additional symptoms: blurred vision (lens osmotic changes from hyperglycaemia), recurrent thrush (Candida vulvovaginitis in women or balanitis in men — hyperglycaemia promotes fungal growth), delayed wound healing, and frequent infections. DKA (diabetic ketoacidosis) — presenting feature in 30-40% of new T1DM diagnoses, particularly in children: rapid-onset (hours to days) of nausea, vomiting, abdominal pain, and fruity-smelling ('pear drop') breath (ketones); tachycardia, dehydration, Kussmaul breathing (deep rapid breathing — respiratory compensation for metabolic acidosis); altered consciousness and coma in severe cases. DKA is a medical emergency with pH below 7.35, bicarbonate below 15 mmol/L, and blood ketones above 3 mmol/L. Hypoglycaemia (blood glucose below 4 mmol/L / 72 mg/dL): major complication of insulin therapy — tremor, sweating, palpitations, hunger (adrenergic symptoms at moderate hypoglycaemia); confusion, difficulty speaking, loss of consciousness, and seizures in severe hypoglycaemia.

Diagnosis of diabetes: fasting plasma glucose above 7.0 mmol/L (126 mg/dL); random plasma glucose above 11.1 mmol/L (200 mg/dL) with symptoms; HbA1c above 48 mmol/mol (6.5%); OGTT 2-hour glucose above 11.1 mmol/L. Type 1 vs. Type 2 differentiation — critical as management differs fundamentally: islet autoantibodies: anti-GAD65 (most sensitive, positive in 70-80% of T1DM), anti-IA-2, anti-ZnT8, anti-insulin — positive in T1DM (or LADA); C-peptide: low or undetectable in T1DM (confirms insulin deficiency); detectable/elevated in T2DM (indicates residual insulin secretion). Urine and blood ketone measurement for suspected DKA. FBC, U&E, LFTs, lipid profile, thyroid function (autoimmune thyroid disease co-exists in 20% of T1DM), coeliac antibodies (tTG-IgA — 5-10% co-prevalence), urine ACR (nephropathy screening from 5 years duration). Annual diabetic eye screening (retinal photography). HbA1c every 3 months (reflects 3-month average blood glucose — target below 48 mmol/mol or individualised). Continuous glucose monitoring (CGM) with Time in Range (TIR) as a key metric — target above 70% time in range (3.9-10 mmol/L).

Insulin is the only treatment for T1DM — it is life-sustaining and lifelong. Physiological insulin regimens: basal-bolus: long-acting basal insulin once or twice daily (glargine U100/U300 — Lantus/Toujeo; detemir — Levemir; degludec — Tresiba) to control fasting glucose + rapid-acting insulin at each meal (aspart — NovoRapid; lispro — Humalog; glulisine — Apidra; ultra-rapid lispro — Lyumjev/URLi). Insulin doses: basal ~0.2-0.3 units/kg/day; total daily dose approximately 0.5-1 unit/kg/day. Carbohydrate counting: 1 unit of insulin per 10-15g carbohydrate (insulin-to-carbohydrate ratio, ICR — varies by individual). Correction dose: calculated by insulin sensitivity factor (ISF or correction factor). CSII (continuous subcutaneous insulin infusion — insulin pump): delivers basal insulin continuously with user-activated boluses; superior glycaemic control vs. MDI for many patients; NICE recommends for: HbA1c above 69 mmol/mol or disabling hypoglycaemia on MDI; used in children of all ages. Continuous glucose monitoring (CGM): Dexcom G7, FreeStyle Libre 3, Medtronic Guardian — real-time glucose with trend arrows; NICE recommends CGM for all people with T1DM; reduces hypoglycaemia and HbA1c. Closed-loop (artificial pancreas) systems: insulin pump + CGM + algorithm automatically adjusting basal insulin; NICE-approved (TA943, 2024) — achieves TIR above 70% in most users and reduces HbA1c by 0.5-1%. Adjunct medications: SGLT2 inhibitors (dapagliflozin — FDA/EMA approved for T1DM in UK, reduces HbA1c 0.4-0.5% with DKA risk); GLP-1 agonists (semaglutide — investigational for T1DM, reduces insulin requirements and weight in overweight T1DM). Annual structured education: DAFNE (Dose Adjustment For Normal Eating) — 5-day course significantly improves HbA1c and quality of life.

Diabetic ketoacidosis (DKA) is the most common acute life-threatening complication — occurring from absolute insulin deficiency, precipitated by illness, missed injections, or at diagnosis; characterised by hyperglycaemia (typically above 14 mmol/L), metabolic acidosis (pH below 7.30, bicarbonate below 15 mmol/L), and ketonaemia (above 3 mmol/L on blood ketone meter). DKA mortality is 0.5–5% overall, higher in elderly patients; cerebral oedema (from rapid osmolarity correction) is the leading cause of death in paediatric DKA — 1–2% of children, 25% mortality. Treatment follows the JBDS fixed-rate IV insulin infusion (FRIII) protocol with weight-based insulin at 0.1 units/kg/hour plus IV 0.9% saline, potassium replacement, and close monitoring. Severe hypoglycaemia (below 3.0 mmol/L with loss of consciousness or seizure) — from insulin excess, missed meals, or exercise — affects 30–40% of T1DM patients annually; hypoglycaemia unawareness (loss of adrenergic warning symptoms after repeated hypoglycaemia) significantly increases the risk; driving restrictions apply; closed-loop insulin pump systems substantially reduce hypoglycaemia risk. Microvascular complications from chronic hyperglycaemia: diabetic retinopathy (leading cause of new blindness in working-age adults — affects 90% of T1DM patients at 30 years; proliferative retinopathy with vitreous haemorrhage and tractional retinal detachment requires panretinal photocoagulation or anti-VEGF injection); diabetic nephropathy (microalbuminuria → proteinuria → CKD → end-stage renal failure in 40% without optimal control — GFR decline 10–15 mL/min/year once clinical proteinuria is established; ACE inhibitors/ARBs are nephroprotective); diabetic peripheral neuropathy (affects 50–60% — painful or painless distal sensory neuropathy, autonomic neuropathy causing gastroparesis, postural hypotension, erectile dysfunction, and anhidrosis). Cardiovascular disease: 2 to 4-fold elevated risk of MI and stroke compared with the general population, even with HbA1c well-controlled.

T1DM itself cannot be prevented currently, but complications are highly preventable with excellent glycaemic control. DCCT trial (USA, 1993): intensive insulin therapy achieving HbA1c below 7% reduced retinopathy by 76%, nephropathy by 50%, and neuropathy by 60% compared to conventional therapy. EDIC follow-up showed benefit persists decades after trial end ('metabolic memory'). Microvascular complication screening (annual from 5 years after diagnosis): diabetic retinopathy (digital retinal photography); nephropathy (urine ACR, eGFR); neuropathy (foot examination, monofilament, vibration). ACE inhibitor or ARB for microalbuminuria (ACR above 3 mg/mmol). Blood pressure target below 130/80 mmHg. Statin therapy from age 40 or earlier with cardiovascular risk factors. Sick day rules: never stop insulin when unwell — increase monitoring; check ketones; maintain fluid intake; seek urgent medical advice for blood ketones above 1.5 mmol/L. DKA prevention: patient education on sick day management; insulin pump users require backup MDI pens. Immunisation: annual influenza; COVID-19 vaccination (T1DM is high-risk group).

Call emergency services (999/911) or go to Emergency Department immediately for: blood glucose above 15 mmol/L with vomiting, abdominal pain, or fruity breath — possible DKA; blood ketones above 3 mmol/L or urinary ketones above 2+ with any illness; severe hypoglycaemia — person unconscious, having seizures, or cannot be roused; hypoglycaemia not responding to 15-20g fast-acting glucose within 15 minutes (use glucagon auto-injector — GlucaGen HypoKit or Baqsimi nasal glucagon). Contact diabetes team or GP urgently for: blood ketones 1.5-3 mmol/L — potential DKA — follow sick day rules and seek advice; repeated hypoglycaemia (more than 2 episodes per week); pregnancy planning — intensive pre-conception glycaemic control reduces miscarriage and congenital malformation risk; new foot ulcer or wound that is not healing normally. Annual review with diabetes team for HbA1c, complications screening, and equipment review.