Lucan · Conditions

Type 1 diabetes mellitus

Australian guidance: ADS Management of Type 1 Diabetes + eTG Diabetes

1. Definition and epidemiology

Type 1 diabetes mellitus (T1DM) is a chronic autoimmune condition characterised by selective destruction of pancreatic beta cells, resulting in absolute insulin deficiency and lifelong dependence on exogenous insulin. It accounts for approximately 10% of all diabetes cases in Australia, with an estimated prevalence of around 130,000 Australians, and the incidence of T1DM in Australian children is among the highest globally at approximately 22 per 100,000 per year. Onset most commonly occurs in childhood or adolescence, though T1DM can present at any age including in adults where it is increasingly recognised as latent autoimmune diabetes in adults (LADA). Corrected 2026-09-22: the captured eTG page states that type 1 diabetes accounts for about 10 to 15% of diabetes cases in Australia, so the flat 10% figure understated the range and has been corrected. The same page records that the incidence peaks in adolescence and early adulthood, not in childhood alone. Not carried by the captured eTG page: the 130,000 Australian prevalence figure and the 22 per 100,000 per year paediatric incidence figure; the page gives the 10 to 15% share and the adolescent and early-adult incidence peak without citing either. Corrected terminology: the captured eTG page states that LADA is "now recognised as a subtype of type 1 diabetes" rather than a separate entity, and supports the diagnosis with elevated type 1 diabetes-associated autoantibodies.

2. Pathophysiology

The pathophysiology of T1DM involves T-cell-mediated autoimmune destruction of insulin-secreting pancreatic beta cells within the islets of Langerhans (Robbins Ch 24 Endocrine). A genetic predisposition conferred primarily by HLA class II alleles (particularly HLA-DR3 and HLA-DR4) lowers the threshold for autoreactive T-cell activation. Environmental triggers, including enteric viral infections and alterations in gut microbiome composition, are proposed to initiate an insulitic process in genetically susceptible individuals. Circulating autoantibodies against islet cell antigens, including anti-glutamic acid decarboxylase (anti-GAD65), anti-insulin antibodies (IAA), and anti-islet antigen 2 (IA-2) antibodies, are detectable months to years before clinical onset, during a subclinical precursor phase. Progressive beta-cell loss reduces insulin secretory reserve until a threshold is reached at which sustained hyperglycaemia occurs. The resulting absolute insulin deficiency prevents cellular glucose uptake and disinhibits hepatic glucose production and lipolysis, predisposing to diabetic ketoacidosis (DKA). Alpha-cell glucagon hypersecretion, unopposed by absent intraislet insulin, amplifies hyperglycaemia.

3. Clinical presentation and diagnostic criteria

The classic presentation is acute onset polyuria, polydipsia, polyphagia with weight loss, and fatigue, typically evolving over days to weeks. Children may present with nocturia or secondary enuresis. DKA at diagnosis occurs in approximately 30% of Australian paediatric cases and is characterised by Kussmaul respirations, fruity ketotic breath, vomiting, abdominal pain, and altered conscious state. In adults, the onset may be more insidious and DKA less common.

Diagnosis requires one of the following with symptoms present (no confirmatory test required): - Random plasma glucose (RPG) of 11.1 mmol/L or above - Fasting plasma glucose (FPG) of 7.0 mmol/L or above

In the asymptomatic individual, two tests on separate days within the diabetes diagnostic range are required to establish diagnosis. HbA1c of 6.5% or above (48 mmol/mol) is accepted as a diagnostic criterion for diabetes in asymptomatic, high-risk individuals; however, the ADS advises that HbA1c is not the preferred diagnostic test when T1DM is suspected clinically, because rapidly evolving hyperglycaemia may not yet have raised HbA1c above the threshold, particularly when symptoms have been present for only a short time.

4. Investigations and AU-specific cutoffs

Initial investigations in suspected T1DM:

1. Blood glucose: RPG 11.1 mmol/L or above with symptoms is diagnostic; FPG 7.0 mmol/L or above confirms on a second occasion if asymptomatic.
2. Blood ketones: capillary beta-hydroxybutyrate 1.0 mmol/L or above indicates significant ketonaemia; values above 3.0 mmol/L are consistent with DKA.
3. Venous blood gas: pH below 7.30 and bicarbonate below 15 mmol/L confirm DKA. Corrected 2026-09-22: the pH below 7.30 is carried by the captured paediatric RCH CPG, but the bicarbonate below 15 mmol/L is not. The RCH CPG uses bicarbonate below 18 mmol/L in the same criterion ("Venous pH <7.3 or bicarbonate <18 mmol/L"), and the captured PCH ED DKA guideline independently uses bicarbonate below 18 mmol/L. The 15 mmol/L figure is the uncaptured adult criterion. Also note the RCH and PCH ED formulations join pH and bicarbonate with or, where this note joins them with and. See dka.md, corrected on the same date.
4. HbA1c: used as a baseline for ongoing glycaemic monitoring (target below 53 mmol/mol or 7.0% for most adults and children; Medicare funds up to four monitoring tests per 12-month period once diabetes is established). Note that conditions reducing red cell lifespan, haemoglobinopathies, iron deficiency, and haemolytic anaemia may render HbA1c unreliable.
5. Autoantibodies: anti-GAD65, IA-2, ZnT8, and IAA to confirm autoimmune aetiology, particularly in adults where T2DM may be misdiagnosed.
6. C-peptide: low or undetectable fasting C-peptide supports absolute insulin deficiency.
7. Full blood count, urea, creatinine, electrolytes, lipids, thyroid function: baseline assessment and exclusion of other autoimmune conditions.
8. Urine albumin-to-creatinine ratio (UACR) and eGFR from the time of diagnosis for baseline renal surveillance.

5. Management

Management of T1DM in Australia is guided by the ADS and involves a multidisciplinary team including an endocrinologist, credentialled diabetes educator (CDE), dietitian, and psychologist where indicated.

Insulin is the only pharmacological therapy for T1DM; a basal-bolus regimen delivered via multiple daily injections (MDI) or continuous subcutaneous insulin infusion (CSII, insulin pump) is the standard of care. The ADS and Australian Diabetes Educators Association jointly endorse the continued use of personal insulin pumps in hospital settings for patients who are metabolically stable, cognitively intact, and able to self-manage their pump. Contraindications to inpatient pump continuation include DKA, critical illness, impaired consciousness, and inability to self-manage the device; in these circumstances, reversion to MDI or intravenous insulin is indicated.

Continuous glucose monitoring (CGM) with real-time interstitial glucose data and integrated alarms is now the preferred monitoring modality for T1DM in Australia and is PBS-subsidised for eligible patients. Automated insulin delivery (AID) systems, which pair insulin pumps with CGM via closed-loop algorithms, are the emerging standard, with hybrid closed-loop systems requiring user input only for bolus dosing at meals. Capillary blood glucose monitoring remains required to validate CGM readings when the interstitial and capillary values diverge by more than 2 mmol/L or when BGL is below 4 mmol/L.

Glycaemic targets: fasting BGL 4.0 to 7.0 mmol/L; two-hour postprandial below 10 mmol/L; HbA1c below 53 mmol/mol (7.0%) for most adults. In hospital, the target BGL range for a patient on insulin pump therapy is 5.0 to 10.0 mmol/L. Corrected 2026-09-22: the captured eTG page's Table 18.3 gives fasting and preprandial 4 to 7 mmol/L (this note's figure, confirmed) but postprandial as a range of 6 to 10 mmol/L, not "below 10"; the lower bound was missing and has been added. The HbA1c target of 53 mmol/mol (7%) or less is confirmed verbatim by the same table. The table also carries four targets this note does not state and which are worth knowing: interstitial glucose range 3.9 to 10 mmol/L, time in range more than 70% (16.8 hours) of the day, time below range less than 4% (60 minutes) of the day below 3.9 mmol/L and less than 1% (15 minutes) below 3.0 mmol/L, and glycaemic variability (%CV) 36% or less. The inpatient pump target of 5.0 to 10.0 mmol/L is not carried by the captured eTG page. Added, carried by the captured eTG page: in adults with newly diagnosed type 1 diabetes the required insulin dose may decline dramatically once glycaemic targets are first achieved, the remission or "honeymoon" phase, which can persist for 6 to 12 months, or occasionally longer.

6. Pharmacology and AU PBS notes

Rapid-acting insulin analogues (bolus): insulin aspart (NovoRapid), insulin lispro (Humalog), insulin glulisine (Apidra). All are PBS-listed on the Pharmaceutical Benefits Scheme (PBS) for T1DM without restriction.

Long-acting insulin analogues (basal): insulin glargine 100 units/mL (Lantus, Basaglar), insulin glargine 300 units/mL (Toujeo), insulin degludec (Tresiba), insulin detemir (Levemir). PBS-listed for T1DM.

Insulin pump cartridges use only rapid-acting analogues (NovoRapid or Humalog) to deliver both basal and bolus requirements. Pump therapy requires referral to an endocrinologist and a CDE for initiation in Australia.

Steroid-induced hyperglycaemia in patients with T1DM on insulin pumps requires at least a 10 to 30% increase in total daily insulin dose, with adjustments to both basal rates and correction boluses; the degree of increase is individually determined and should be managed in conjunction with the local Endocrinology/Inpatient Diabetes Team.

No PBS streamlined authority codes apply to insulin for T1DM; all insulins are available on unrestricted PBS benefit for established T1DM.

7. Complications and monitoring

Acute complications: DKA (most serious acute complication; management includes IV fluid resuscitation, fixed-rate insulin infusion, potassium replacement, and identification of precipitant), hypoglycaemia (BGL below 4.0 mmol/L; risk compounded by AID systems and strenuous exercise).

Chronic microvascular complications (Robbins Ch 24 Endocrine): diabetic retinopathy, nephropathy, and peripheral and autonomic neuropathy. All are related to duration of hyperglycaemia and glycaemic variability.

Chronic macrovascular complications: accelerated atherosclerosis leading to ischaemic heart disease, stroke, and peripheral arterial disease. Cardiovascular risk management (blood pressure, lipids, smoking cessation) is integral to T1DM care.

Surveillance schedule: - HbA1c: three-monthly until stable, then six-monthly - Annual: UACR and eGFR (renal), fasting lipids, blood pressure, foot examination (10-g monofilament, ankle reflexes, pedal pulses), dilated fundoscopy or retinal photography from 5 years post-diagnosis or at puberty, thyroid function (anti-TPO antibodies at diagnosis; TSH annually given co-occurrence of autoimmune thyroid disease) - Coeliac disease screening: anti-tissue transglutaminase IgA at diagnosis and at 2 years, given shared autoimmune predisposition - Bone health: DXA at clinician discretion in those with prolonged poor glycaemic control - Psychological wellbeing: routine screening for diabetes distress and depression at every contact

Written for Australian practice and grounded in the guidance named above. Study material only — not medical advice. Always check against current guidelines.