Type 1 Diabetes: Symptoms, Diagnosis & NHS Treatment

Type 1 diabetes is an autoimmune condition in which the immune system destroys the insulin-producing beta cells of the pancreas, causing near-total insulin deficiency. It affects approximately 400,000 people in the UK. Unlike type 2 diabetes, type 1 is not caused by lifestyle factors — it can develop at any age but most commonly begins in childhood, adolescence, or young adulthood. Type 1 diabetes requires lifelong insulin therapy. Advances in technology — including continuous glucose monitors (CGMs) and hybrid closed-loop insulin pump systems — have transformed diabetes management and quality of life.

What Is Type 1 Diabetes?

In type 1 diabetes, the immune system — via T lymphocytes and autoantibodies — destroys the insulin-producing beta cells of the islets of Langerhans in the pancreas. The trigger for this autoimmune process involves a combination of genetic susceptibility (HLA-DR3 and HLA-DR4 alleles are strongly associated, accounting for approximately 50% of genetic risk; non-HLA gene variants contribute the remainder) and environmental factors (possible role of early viral infections, gut microbiome, and reduced early childhood microbial exposure — the “hygiene hypothesis”). As beta cell mass is destroyed, insulin secretion falls, and when approximately 80–90% of beta cells are lost, clinical diabetes develops.

Without insulin, glucose cannot enter cells — blood glucose rises (hyperglycaemia), and the body breaks down fat for energy, producing ketone bodies. Accumulation of ketones causes diabetic ketoacidosis (DKA) — the acute life-threatening presentation of uncontrolled type 1 diabetes. DKA remains the most common cause of diabetes-related death in young people and is often the mode of first diagnosis.

Symptoms of Type 1 Diabetes

The classic symptoms of type 1 diabetes reflect uncontrolled hyperglycaemia and the body’s response to insulin deficiency. They develop over days to weeks and include: polydipsia (excessive thirst); polyuria (frequent urination, including at night); unexplained rapid weight loss; extreme fatigue; blurred vision; genital itching or thrush; and in children, bedwetting after previously being dry. These symptoms, particularly in children and young adults, should prompt urgent blood glucose testing — do not wait for a GP appointment if DKA is suspected.

Signs of diabetic ketoacidosis (DKA) — which may be the presenting feature — include: nausea and vomiting; abdominal pain; deep, rapid breathing (Kussmaul respiration); fruity or acetone-smelling breath (from exhaled ketones); confusion; and collapse. DKA is a medical emergency requiring immediate hospital treatment. Any child or young person with unexplained vomiting and rapid breathing should have an urgent blood glucose check.

Diagnosing Type 1 Diabetes

Diagnosis is based on standard WHO/NICE blood glucose criteria: fasting plasma glucose ≥7.0 mmol/L, or random plasma glucose ≥11.1 mmol/L with symptoms, or HbA1c ≥48 mmol/mol (in non-acute presentations). Children presenting with symptoms are usually diagnosed clinically without requiring a second confirmatory test. Adults presenting with apparent type 2 diabetes but with features suggesting T1D should be tested for islet autoantibodies (particularly anti-GAD antibodies — positive in approximately 80% of T1D cases) and C-peptide (a marker of residual insulin secretion — very low or undetectable in established T1D).

Distinguishing type 1 from type 2 in adults is important — features that suggest T1D include: age under 35 at presentation; normal or low BMI; no features of metabolic syndrome; rapid deterioration requiring insulin; previous DKA; and positive autoantibodies. Misclassification of adult-onset T1D as T2D is common and delays appropriate management.

Latent autoimmune diabetes in adults (LADA) — sometimes called “type 1.5 diabetes” — is a slower-onset autoimmune diabetes in adults who initially respond to non-insulin therapies but progressively require insulin. Anti-GAD positivity with preserved C-peptide initially helps distinguish LADA from T2D.

NHS Treatment: Insulin Therapy (NICE NG17)

Insulin replacement is the cornerstone of T1D management. Modern insulin regimens mimic physiological insulin secretion. The gold standard is a basal-bolus regimen — a long-acting basal insulin (insulin glargine — Lantus, Toujeo; insulin detemir — Levemir; insulin degludec — Tresiba) given once or twice daily to provide background insulin, plus a short-acting or rapid-acting insulin analogue (insulin aspart — NovoRapid; insulin lispro — Humalog; insulin glulisine — Apidra; ultra-rapid insulin, e.g., Fiasp) given with meals to cover carbohydrate intake. Dose adjustment for eating (DAFNE — Dose Adjustment For Normal Eating) is a structured education programme offered to all adults with T1D, teaching flexible insulin dosing based on carbohydrate counting.

Continuous subcutaneous insulin infusion (CSII) — insulin pump therapy — delivers insulin via a pump connected to a cannula inserted subcutaneously. Pumps deliver a programmable basal rate and patient-activated boluses with meals. NICE recommends insulin pump therapy for adults and children with T1D who have inadequate HbA1c control or disabling hypoglycaemia on multiple daily injections (MDI). Hybrid closed-loop systems (“artificial pancreas”) — which combine an insulin pump with a CGM and an algorithm that automatically adjusts basal insulin delivery based on real-time glucose readings — have been recommended by NICE for adults and children with T1D. These systems significantly reduce time in hypoglycaemia and time outside the target glucose range, and improve quality of life.

Continuous Glucose Monitoring (CGM)

Continuous glucose monitoring (CGM) measures interstitial glucose continuously, providing real-time and trend data. Two main types: real-time CGM (rtCGM — alerts for high and low glucose; worn continuously; e.g., Dexcom G6, G7) and intermittently scanned CGM (isCGM/flash glucose monitoring — requires user to scan the sensor; e.g., Freestyle Libre 2). From 2022, NICE recommended that all people with T1D in England on MDI or CSII should have access to CGM (rtCGM or isCGM) on the NHS. CGM replaces fingerprick testing for most glucose monitoring and significantly improves time in range, reduces HbA1c, and reduces severe hypoglycaemia.

Key CGM metrics: time in range (TIR — the percentage of time with glucose 3.9–10.0 mmol/L; target ≥70% for most adults with T1D); time below range (TBR — glucose below 3.9 mmol/L; target less than 4%); time above range (TAR — glucose above 10 mmol/L; target less than 25%); GMI (glucose management indicator — estimated HbA1c from CGM data).

Managing Hypoglycaemia

Hypoglycaemia (low blood glucose, typically below 3.9 mmol/L) is the most common acute complication of insulin therapy. Symptoms include: shakiness, sweating, palpitations, hunger (adrenergic symptoms); and confusion, difficulty concentrating, drowsiness, and slurred speech (neuroglycopenic symptoms). Treatment of conscious hypoglycaemia: 15–20 g of fast-acting carbohydrate (glucose tablets, Lucozade, fruit juice, or sugary drinks — NOT chocolate, biscuits, or fruit bars, which are too slowly absorbed). Re-check glucose after 15 minutes; repeat if still below 4 mmol/L. After recovery, eat a carbohydrate-containing snack if the next meal is more than 1 hour away.

Severe hypoglycaemia — requiring third-party assistance — is treated with glucagon (Glucagen, Baqsimi nasal powder — available on NHS for household members to administer). All people with T1D should have emergency glucagon prescribed. Hypoglycaemia unawareness — reduced or absent warning symptoms before severe hypoglycaemia — affects approximately 20–25% of people with T1D and is a serious safety concern. rtCGM with low glucose alarms significantly reduces the risk of severe hypoglycaemia and is particularly important for people with hypoglycaemia unawareness.

Long-Term Complications

Chronic hyperglycaemia causes microvascular complications — diabetic retinopathy (leading cause of blindness in working-age adults); diabetic nephropathy (a major cause of end-stage renal failure); and diabetic peripheral neuropathy — and macrovascular complications (coronary artery disease, stroke, peripheral arterial disease). Annual diabetes reviews assess HbA1c, blood pressure, lipids, eGFR and urine ACR, retinal screening, and foot examination. The risk of complications is significantly reduced by maintaining HbA1c close to the target (typically 48–58 mmol/mol), controlling blood pressure (below 130/80 mmHg), and using statins for cardiovascular risk reduction in adults over 40 or with existing cardiovascular risk factors.