27th May 2025

Diagnosis

Clinical Presentation

T1DM mostly presents in childhood and most commonly diagnosed aged 10-14 years. There are three possible initial presentations including classical presentation, diabetic ketoacidosis and silent (asymptomatic) discovery.

The classical presentation in children and young people is hyperglycaemia without acidosis. Patients typically present with the triad of symptoms of polydipsia, polyuria or nocturia and weight loss. These symptoms are usually present in about 90% of patients but may not be the initial complaint. Other symptoms include dry mouth, lethargy and blurred vision. Presentations can include perineal candidiasis in young children and girls, acute visual disturbances and cataracts.

• Polydipsia occurs due to increased thirst as a result of increased plasma osmolality from hyperglycaemia. 
• Polyuria occurs when the glucose concentration rises above the renal threshold which leads to increased urinary glucose excretion, glycosuria causes osmotic diuresis which presents as polyuria and hypovolaemia and dehydration. In children, polyuria can present as excess wet nappies, bedwetting and daytime incontinence in a previously continent child.
• Weight loss occurs as a result of hypovolaemia and catabolism resulting in loss of calories (glucose) through urine, it is present in about 50% of patients. As a result of insulin deficiency, there is dysregulation of glucose utilisation in peripheral muscle and adipose tissue resulting in breakdown of muscle and fat. As polydipsia develops, patients are more thirsty than hungry and they develop nausea and anorexia from ketosis which contributes to weight loss further.

Diabetes ketoacidosis (DKA)  is the second most common presentation of T1DM (30% to 50% of children under 3 years). DKA can be severe and life threatening, it requires hospitalisation for rehydration and insulin therapy. Signs and symptoms of DKA include 

• Nausea and vomiting 
• Abdominal pain
• Dehydration 
• Tachypnoea
• Drowsiness 
• Fruit-smelling (‘pear drop’) ketotic breath 
• Coma

Silent or asymptomatic discovery is the least common presentation where children are diagnosed before the onset of clinical symptoms. It is usually seen in children that are being closely monitored by a family member or clinician with high suspicion.

Investigations

In order to diagnose T1DM, a diagnosis of diabetes mellitus (DM) needs to be established.

Diagnosis of DM

• Capillary blood glucose, capillary ketones and urine dipstick can be indicators of T1DM but should not be used to make a formal diagnosis. 
• Venous blood glucose: fasting blood glucose ≥7.0 mmol/L or non-fasting blood glucose ≥11.1 mmol/L. 
• Oral glucose tolerance test (OGTT): venous blood glucose ≥11.1 mmol/L, 2 hours after ingesting 75 g oral glucose. 
• Glycosylated haemoglobin (HbA1c) ≥48 mmol/mol (≥6.5%).

Diagnosis of T1DM

The diagnosis of T1DM is usually made by the investigations above in the setting of clinical presentation as mentioned. If the diagnosis is unclear, autoantibodies and fasting C-peptide can be used. 

• Autoantibodies to islet cells, islet antigens (IA2, IA2-beta), insulin, glutamic acid decarboxylase (GAD) or zinc transporter ZnT8.
• Fasting C-peptide level is low or undetectable in T1DM as C-peptide is a product of endogenous insulin production.