Type 1 diabetes

Routine adult GP care of type 1 diabetes, complementing Diabetes – diagnosis (shared diagnostic thresholds and classification), Diabetes – complications and DKA & HHS (the acute hyperglycaemic emergencies). For intercurrent illness, see the dedicated Sick Day Management of T1DM page. For patients under 16, insulin initiation is via paediatric referral, not this page.

Pathophysiology and presentation

T-cell-mediated autoimmune destruction of pancreatic beta cells → absolute insulin deficiency and lifelong insulin dependence. Often presents young with a brief (2–10 week) history of polyuria, polydipsia and weight loss, and may present in diabetic ketoacidosis.

• Antibodies — GAD, IA-2, ZnT8, and insulin autoantibodies; ~80% are GAD/IA-2 positive. Useful to confirm type 1 where the phenotype is ambiguous.
• LADA (latent autoimmune diabetes in adults) — slowly-progressive type 1 presenting ~30–40 years, often initially resembling type 2 but progressing to insulin dependence; suspect it in a lean adult with a poor response to oral agents or other autoimmune disease. GAD antibodies confirm it.
• C-peptide (low/undetectable) can help distinguish from type 2 when needed.

At first presentation, collect the associated autoimmune screen: coeliac serology (total IgA, tTG), TSH and fT4 (autoimmune thyroid disease is common). Main causes of mortality differ by age — under 30, hypoglycaemia, DKA and suicide related to diabetes-associated mental health problems; over 30, cardiovascular death.

Insulin therapy

• Basal insulin (Optisulin, Toujeo or Levemir) once or twice daily — relationship to meals doesn’t matter; the goal is a stable fasted/overnight glucose. Never omit basal insulin, even when unwell — the single biggest preventable cause of DKA.
• Bolus (mealtime) insulin — an ultra-rapid analogue (NovoRapid, Apidra, Fiasp, Humalog) 15 minutes before meals, dosed to a personal insulin-to-carbohydrate ratio (e.g. 1 unit per 15 g carbohydrate). Persistently high/low post-meal glucose suggests inaccurate carb counting (consider dietitian referral), insulin given too late/omitted, or a ratio needing adjustment.
• Correction dose — additional rapid-acting insulin given with a meal to correct a high pre-meal glucose, on top of the regular bolus, usually expressed as a ratio (e.g. 1 extra unit per 2 mmol/L above 8 mmol/L).
• Insulin pump (CSII) — rapid-acting insulin only. Modern pumps in “auto-mode”/hybrid closed-loop adjust basal delivery from CGM data; time in auto-mode <90% of 24 hours suggests settings need review. Patients still manually bolus for meals. All pump users need a CGM, a ketone meter, and a personalised pump failure plan.

Factors changing insulin requirements: exercise (reduce dose or increase carbohydrate beforehand; delayed hypoglycaemia can persist up to 24 hours afterwards, sometimes needing a lower overnight basal dose); alcohol (consume with food, ≤2 standard drinks/day with 2 alcohol-free days/week per general population advice; reduce long-acting insulin 10–20% on binge days — hypoglycaemia risk is delayed and compounded by exercise); concurrent illness (requirement usually increases, even without eating, from infection-induced insulin resistance — see the sick day page); injection-site lipohypertrophy (rotate sites — alters absorption); gastroparesis (delayed/ erratic absorption); and recreational drugs (THC can cause cannabis-induced hyperemesis; amphetamines complicate titration via anorexia and poor dentition).

Clinical editor’s note (HNE HealthPathways, 4 May 2026): Novo Nordisk is discontinuing Protaphane Penfill, Levemir FlexPen/Penfill, Actrapid Penfill and NovoFine Autocover from December 2026 — check any patient still using these has a documented alternative before the changeover.

Insulin pump failure

If a pump stops delivering insulin, ketosis can develop within hours — contact the pump company immediately (most troubleshoot by phone and can arrange a loan pump within 2–5 days) and bridge with subcutaneous injections in the meantime:

• If the patient knows their pump’s total daily insulin dose: give 50% as long-acting insulin once daily, and 50% as rapid-acting mealtime boluses split evenly across breakfast, lunch and dinner.
• If unknown and no current pump backup plan exists: estimate long-acting insulin at 0.3 units/kg/24 h, and rapid-acting insulin at 0.1 units/kg with each main meal (e.g. a 60 kg patient: ~18 units long-acting daily, ~6 units rapid-acting with each meal) — an approximation only, to avoid hospitalisation until the pump is replaced.
• Refer to ED for vomiting, dehydration, ketones, or BGL >20 mmol/L.
• Ensure the patient has a current long-acting insulin script, correct needles/syringes, and knows how to inject — this is why every pump user needs a documented, personalised backup plan in advance, not worked out at the time of failure.

Continuous glucose monitoring (CGM)

CGM reduces severe hypoglycaemic events, improves control in those with poor glycaemic awareness, reduces emergency presentations and reduces anxiety. All patients with type 1 diabetes are eligible for partially/fully NDSS-subsidised CGM, following assessment by an authorised health professional (endocrinologist, credentialed diabetes educator, or other diabetes-experienced clinician) to confirm eligibility and choice of device. Offer CGM to anyone not already using it.

A blood glucose meter capable of blood ketone testing is needed by every patient with type 1 diabetes — blood ketone testing is preferred over urine because it’s more accurate, gives earlier warning of ketosis, and avoids the practical barriers of urine testing (unpleasant, slower, a colour-read result that’s hard to interpret with poor vision, and only semi-quantitative).

Hypoglycaemia

A severe hypoglycaemic episode is one the patient cannot treat themselves — requiring third-party assistance or glucagon. Screen for hypoglycaemia unawareness (failure of the autonomic warning response, usually from preceding frequent hypoglycaemia) by asking: at what glucose level do symptoms first appear; has a hypo ever been picked up by a family member before the patient noticed; do meter readings <4 mmol/L ever occur without symptoms (readings <2 mmol/L are a major unawareness warning sign); and — for rebound hyperglycaemia — are there unexplained readings both <4 and >18 mmol/L. HbA1c does not reflect hypoglycaemia risk at any level, so ask directly regardless of control.

Provide a glucagon prescription and train a household member to use it. Advise checking BGL immediately before driving (must be >5 mmol/L) and being aware of CGM low-glucose alerts.

Driving: a conditional private licence (Transport for NSW, ≥2-yearly review) requires no recent severe hypoglycaemic event, a treatment regimen minimising hypoglycaemia risk, awareness of early warning symptoms (screen with the Clarke hypoglycaemia awareness survey if unsure) or a documented plan for lack of awareness, and no relevant end-organ effects. Do not drive for at least 6 weeks after a severe hypoglycaemic event (time for control and any impaired awareness to re-settle). Commercial drivers need annual specialist review; routine licensing reviews are not accepted by public diabetes clinics — arrange this through the patient’s own specialist.

Sick days

Never stop or reduce basal insulin because of reduced oral intake — vomiting and diarrhoea can lower glucose but insulin needs typically still rise with acute illness, and stopping basal insulin risks DKA. See the Sick Day Management of T1DM page for ketone interpretation, supplemental insulin dosing, fluid/carbohydrate rules and ED thresholds.

Monitoring and cycle of care

General glycaemic targets: HbA1c ≤53 mmol/mol (7%); BGL 4–7 mmol/L fasting/preprandial; 6–10 mmol/L two hours postprandial. Individualise higher in the elderly, with severe hypoglycaemia/unawareness, or with major comorbidities limiting life expectancy — balance tight control against hypoglycaemia risk.

• HbA1c — 3-monthly until at target, then 6–12-monthly.
• Every 6 months — BMI/waist circumference; blood pressure (ACE inhibitor or ARB first-line, never combined, target ≤130/80 unless elderly/comorbid/postural hypotension; switch away from ACEi/ARB before conception, not just once pregnant).
• Every 12 months — lipids (total cholesterol <4.0, HDL-C ≥1.0, LDL-C <2.0 [<1.8 with established CVD], non-HDL <2.5, triglycerides <2.0 mmol/L; avoid lipid-lowering drugs in women planning pregnancy or on inadequate contraception except on specialist advice); eGFR and urine ACR; an autoimmune screen (TFT, B12, FBC with ferritin to screen for active coeliac disease).
• Every 2 years — comprehensive dilated eye examination.
• Foot examination — every 1–3 months (high-risk feet), 3–6 months (at-risk), or 12 months (low-risk) — see Diabetes-related foot disease.
• Mental health — depression and anxiety are at least four times more common than in age-matched controls. Screen for diabetes distress and burnout with open questions (“what’s the most difficult part of living with diabetes for you?”) or the PAID scale (total ≥40/100 = severe distress; any item ≥3 = a problem area) and PHQ-2 (≥3 = positive depression screen). Watch for insulin omission as a marker of a concurrent eating disorder, particularly with otherwise-unexplained weight loss or acute loss of control.
• Immunisations — influenza, pneumococcal, zoster and COVID-19 per standard schedules.
• Pregnancy — arrange preconception specialist review 12–24 months ahead where possible; if already pregnant, urgent maternity or private endocrinology referral (seen within 1 week) for early review, with tighter glycaemic targets (HbA1c ≤6.5% planning, ≤6% once pregnant).

Referral

Urgent diabetes specialist review for: a severe hypoglycaemic event or increased hypoglycaemia frequency; post-DKA-admission follow-up; newly diagnosed or suspected type 1 diabetes; HbA1c >12% (108 mmol/mol) or average BGL >14 mmol/L despite escalated therapy; or new steroid therapy (pulse steroids or chemotherapy) in an existing type 1 patient.

Non-urgent specialist review for: diabetes distress/burnout; HbA1c >10% (86 mmol/mol) or average BGL 10–14 mmol/L; uncontrolled cardiovascular risk factors; suspected disordered eating; newly diagnosed coeliac disease; emerging complications affecting insulin needs (CKD stage ≥3, pre-proliferative/proliferative retinopathy, new peripheral or autonomic neuropathy, recent acute coronary/cerebrovascular event); First Nations or otherwise vulnerable patients; paediatric-to-adult transition; and insulin pump initiation, dose adjustment or upgrade.

Credentialed diabetes educator for insulin/pump/CGM technique concerns, hypoglycaemia education, or equipment issues. Dietitian if not seen in the last 5 years, for carbohydrate-counting review. Psychology/eating-disorder services for diabetes distress, mental health comorbidity, or disordered eating.