Type 1 Diabetes — Symptoms, Causes & Treatment | MyMedicPlus

Type 1 diabetes mellitus (T1DM) is a chronic autoimmune disease in which the body's immune system selectively destroys pancreatic beta cells — the insulin-producing cells of the islets of Langerhans — resulting in absolute insulin deficiency. Without exogenous insulin, glucose cannot enter cells for energy metabolism, leading to hyperglycaemia, accelerated fat breakdown into ketone bodies, and without treatment, rapidly fatal diabetic ketoacidosis (DKA). T1DM accounts for 5-10% of all diabetes cases globally — approximately 8.7 million people worldwide. The condition has two peak ages of onset: early childhood (4-7 years) and periadolescence (10-14 years), but onset can occur at any age — up to 40% of new T1DM diagnoses occur in adults, where it is frequently misdiagnosed as type 2 diabetes ('latent autoimmune diabetes in adults' — LADA). The condition is entirely unrelated to lifestyle choices — it cannot be prevented or caused by diet or physical inactivity. With appropriate insulin replacement and glucose monitoring technology, people with T1DM can lead healthy, active lives with near-normal life expectancy. Advancing technology — continuous glucose monitors (CGMs) and hybrid closed-loop insulin delivery systems (artificial pancreas) — has transformed management outcomes significantly over the past decade.

T1DM results from autoimmune CD4+ and CD8+ T-cell-mediated destruction of pancreatic beta cells, triggered by environmental factors in genetically susceptible individuals. By the time clinical symptoms develop, typically 80-90% of beta-cell mass has been destroyed. Genetic susceptibility: HLA (human leukocyte antigen) class II alleles are the strongest genetic determinants — HLA-DR3/DQ2 and HLA-DR4/DQ8 haplotypes confer 3-4-fold increased risk; a non-HLA gene DI (insulin gene region on chromosome 11p) modulates thymic insulin expression. Concordance in identical twins is approximately 50% — confirming that genetic factors alone are not sufficient, and environmental triggers are required. Autoimmunity: multiple autoantibodies are present years before clinical diagnosis — anti-glutamic acid decarboxylase (GAD65 — the most commonly positive, in 70% of new cases), islet antigen-2 (IA-2), zinc transporter 8 (ZnT8), and insulin autoantibodies (IAA — the first to appear in young children). Environmental triggers: enteroviral infections — particularly Coxsackievirus B — have the strongest epidemiological evidence for triggering islet autoimmunity; childhood gut microbiome composition and diversity (hygiene hypothesis — reduced microbial exposure in early life; higher incidence in high-income industrialised countries); low vitamin D levels (vitamin D modulates immune tolerance); gluten exposure (coeliac disease and T1DM share HLA associations and frequently coexist — 5-10%); and perinatal factors (caesarean section, formula feeding). Risk is 5% in a child of an affected mother, 8% with an affected father, and 30% if both parents have T1DM.

Classic 4T presentation: Thirsty (polydipsia — excessive thirst driven by osmotic diuresis from hyperglycaemia), Tired (profound fatigue and malaise from cellular glucose starvation), Thinner (rapid unexplained weight loss — from glucose loss in urine and catabolism of fat and muscle), Toilet (polyuria from glycosuria — glucose spills into urine above renal threshold of 10 mmol/L, drawing water osmotically; nocturia). Additional symptoms: polyphagia (paradoxically increased hunger despite weight loss — from cellular glucose starvation); blurred vision (osmotic changes in the lens from hyperglycaemia — resolves with treatment); recurrent infections (thrush/candidiasis, skin infections, balanitis in men — glucose-enriched urine and mucous membranes promote fungal and bacterial growth). Diabetic ketoacidosis (DKA — often the first presentation in children and young adults): nausea and vomiting; diffuse abdominal pain; fruity (acetone/pear-drop) breath odour; rapid deep sighing respirations (Kussmaul breathing — respiratory compensation for metabolic acidosis); lethargy progressing to altered consciousness; and dehydration. DKA is more common in children at first diagnosis and in patients with intercurrent illness who stop insulin. Blood glucose is typically above 15-20 mmol/L; blood or urinary ketones elevated (above 1.5 mmol/L); venous pH below 7.3.

Standard diabetes diagnostic criteria: fasting plasma glucose above 7.0 mmol/L; random plasma glucose above 11.1 mmol/L with symptoms; HbA1c above 6.5% (48 mmol/mol) — in T1DM, HbA1c may be unreliable if haemoglobin variants are present or in rapid-onset DKA. Two positive tests are required in asymptomatic individuals. Autoantibody panel to confirm autoimmune T1DM: anti-GAD65 (positive in 70% of new T1DM cases — the most useful single antibody test); anti-IA-2; anti-ZnT8; insulin autoantibodies (IAA — highest specificity in young children before exogenous insulin is started). Positivity of any autoantibody strongly supports T1DM over T2DM. C-peptide measurement: low or undetectable (below 0.2 nmol/L — reflects absent endogenous insulin secretion) — distinguishes T1DM from T2DM where C-peptide is normal or elevated. MODY (maturity-onset diabetes of the young) genetic testing: appropriate if atypical features — no ketosis at presentation, strong family history of diabetes in successive generations, normal BMI, autoantibody-negative, and onset under 25. Common MODY subtypes: MODY2 (GCK gene — mild stable hyperglycaemia) and MODY3 (HNF1A — responds well to sulphonylureas). Coeliac antibodies (anti-tissue transglutaminase tTG IgA): 5-10% of T1DM patients have coeliac disease — routine screening recommended at diagnosis. Thyroid function tests and thyroid antibodies: autoimmune thyroid disease (Hashimoto's or Graves') is present in 15-30% of T1DM patients. Ketone testing: blood ketones (above 1.5 mmol/L — significant) or urinary ketones for DKA assessment.

Insulin is essential, lifesaving, and must never be stopped — even during illness when oral intake is reduced (sick day rules must be taught to all T1DM patients). Multiple daily injection (MDI) basal-bolus regimen: long-acting basal insulin (insulin glargine U-100/U-300, insulin degludec) injected once or twice daily to provide background insulin coverage; plus rapid-acting bolus insulin (insulin aspart, lispro, glulisine) injected before each meal, dosed by carbohydrate-counting (typically 1 unit per 10-15 g carbohydrate plus correction for current glucose level). This regimen best mimics physiological insulin secretion. Continuous subcutaneous insulin infusion (CSII — insulin pump therapy): a programmable device delivers basal insulin continuously and bolus doses at mealtimes — provides more precise control, reduces hypoglycaemia, and improves HbA1c by approximately 0.5% compared to MDI; NICE recommends pumps for adults with recurrent hypoglycaemia or suboptimal control despite MDI. Continuous glucose monitoring (CGM): a sensor inserted subcutaneously measures interstitial glucose every 1-5 minutes — Freestyle Libre (flash — scan-activated) or Dexterity G7 (real-time — with alarms for high/low glucose); CGM reduces HbA1c by 0.5-1%, dramatically reduces hypoglycaemia, and improves time-in-range (TIR — the percentage of time glucose is between 3.9-10 mmol/L; target above 70%); NICE (TA943) recommends CGM for all T1DM adults and children. Hybrid closed-loop ('artificial pancreas'): CGM integrated with an insulin pump and an algorithm that automatically adjusts insulin delivery — e.g., Omnipod 5, CamAPS FX with Mylife YpsoPump; reduces hypoglycaemia, improves overnight glucose, and substantially reduces management burden; NICE approved. Target HbA1c: below 7% (53 mmol/mol) for most adults. Adjunct therapy: sodium-glucose cotransporter-1 inhibitors (SGLT-1/2 inhibitors — sotagliflozin — licensed in some countries as adjunct to insulin in T1DM; requires careful patient selection due to ketoacidosis risk).

Acute complications: diabetic ketoacidosis (DKA) — the most serious acute complication; triggered by missed insulin doses or intercurrent illness; mortality below 1% in specialist centres but remains significant in low-income settings. Hypoglycaemia: blood glucose below 4 mmol/L — the most common and feared complication; severe hypoglycaemia (requiring external assistance) affects 30-40% of T1DM patients annually; causes include excessive insulin, reduced carbohydrate intake, and exercise; impaired hypoglycaemia awareness (loss of warning symptoms) affects 25% of long-term T1DM patients and dramatically increases severe hypoglycaemia risk; CGM and hybrid closed-loop systems reduce hypoglycaemia significantly. Chronic microvascular complications from prolonged hyperglycaemia: diabetic retinopathy (affects 60-80% after 20 years — the leading cause of blindness in working-age adults; classified as non-proliferative or proliferative; treated with laser photocoagulation, anti-VEGF injections, or vitrectomy); diabetic nephropathy (affects 20-40% of T1DM patients; progresses through microalbuminuria to macroproteinuria and CKD; managed with ACE inhibitors or ARBs); diabetic peripheral neuropathy (painful or sensory loss in a glove-and-stocking distribution — affects 50% after 25 years; autonomic neuropathy causes gastroparesis, orthostatic hypotension, erectile dysfunction, and hypoglycaemia unawareness). Macrovascular complications: cardiovascular disease risk is 2-4 times higher than the general population.

Call 999/112 immediately for: symptoms of diabetic ketoacidosis (DKA) — severe vomiting preventing fluid intake, rapid or deep breathing (Kussmaul breathing), fruity breath odour, confusion or drowsiness, very high blood glucose (above 15 mmol/L with ketones above 1.5 mmol/L — test with a ketone meter), or blood glucose below 4 mmol/L with loss of consciousness (severe hypoglycaemia). Treat mild to moderate hypoglycaemia (blood glucose below 4 mmol/L with symptoms) immediately with fast-acting glucose: 4-6 glucose tablets, 150 mL non-diet fruit juice, or 5 glucose sweets — then a carbohydrate snack; repeat blood glucose in 15 minutes. All people with Type 1 diabetes should attend annual review with their diabetes team including: HbA1c, eye screening (retinal photography), renal function and urine ACR, foot examination, blood pressure and lipids, and injection site review. Contact your diabetes team promptly for: HbA1c consistently above target, frequent hypoglycaemia episodes, new or worsening complications, illness management (sick day rules), or before planned pregnancy (preconception HbA1c below 48 mmol/mol reduces congenital malformation risk).

No proven prevention for T1DM itself — it is an autoimmune disease unrelated to lifestyle. Teplizumab (an anti-CD3 T-cell monoclonal antibody — Tzield) delays clinical onset in at-risk stage 2 T1DM individuals (autoantibody-positive with dysglycaemia) by a median of 3 years — FDA-approved November 2022; a landmark development in disease modification. Structured patient education: DAFNE (Dose Adjustment For Normal Eating) training empowers patients for flexible insulin-to-carbohydrate ratio dosing — reduces hypoglycaemia and HbA1c. Annual complication screening: HbA1c, eGFR and urine ACR (diabetic nephropathy), retinal photography (diabetic retinopathy — the leading cause of blindness in working-age adults), foot sensation and pulse examination, blood pressure, and fasting lipid profile. Sick-day rules education (never stop insulin during illness even if not eating; increase monitoring frequency to every 2 hours; check ketones; contact diabetes team early if ketones above 0.6 mmol/L) — reduces DKA hospital admissions. Annual influenza vaccination; pneumococcal and COVID-19 vaccines as recommended. Hybrid closed-loop insulin delivery (artificial pancreas) and CGM access significantly improve time-in-range and reduce both hypoglycaemia and hyperglycaemia burden.